EFI Fuel Pump Failure Risk

[dmattmul]

Andair fuel valve fittings ?

I always run both electric fuel pumps for Takeoffs and landings on my SDS system installed on IO-540 in RV10.

I am based at 2500', running 93 Octane E10 , have about 300 hours on the system. No issues to date. I have the standard Andair fuel valve and no 90 degree fittings on the suction side.

I am gland some of us now can read a pump curve. Useful data.

So you are not using 90's on the inlet side of your fuel valve? (Suction line, fitting on the Andair valve) I wish I could have avoided doing this (10 and 14 had to use 90's on the suction and discharge side of the valve) and would love to see any pictures how this was done.

Has anyone taken a manometer and measured the suction during a fuel tank transfer? Granted most don't turn the transfer valve slowly but when I do mine slowly, I hear a difference in flow and fuel pressure changes albeit slightly. I can only hear this on the ground with engine off.

 

[TASEsq]

Poll on pump use - SDS vs EFII

Thank you all for your valuable feedback.

It seems there anecdotally 2 camps: the SDS camp who are happy to run both pumps at once (with operational experience out there), and the EFII camp, who don't run 2 pumps at once (but i haven't heard any actual operational anecdotes on what happens if you do using EFII).

I will try and add a POLL to see what the numbers of each are? Would be good to know if there are an SDS users who don't run 2 pumps, or vice versa (EFII users who do).

What is puzzling to me is that in most setups as far as i can tell, both systems use basically the same. Everyone is using the FS20 duplex fuel valve, everyone avoids hard 90 turns at the suction side of the fuel selector as best they can, and both systems use Walbro GSL393 pumps.

So why is there any operational difference between the 2 with regard to how fuel makes it to the engine?

Assuming:
1. i don't like the risk of a single pump running for take-off and
2. I don't like the SPOF if the bus manager or similar units which provide automatic switching of the pumps and
3. I am probably leaning toward the EFII system, solely because i like the system controller a lot more (vain? maybe!).

My takeaway from what everyone is telling is me, is that i have 2 design options:
1. Simple. 2 breakers, 2 switches (maybe 2 relays if i choose) and 2 pumps. Turn both switches on for take-off and landing despite Robert's cautions (eek!)
or
2. A bit more complicated. 2 breakers, 2 relays, one switch, a pressure sensor switch (20 psi?) and a latching relay and brew my own automatic pressure sensing system to turn on the second pump if the output of the first fails**.

Unless there are any EFII users out there who can substantiate why the EFII system is different from the SDS system i think just turning on 2 pumps for take-off and landing is much more robust than a home made switching system. I do like the idea of a pressure switch in the system somewhere which can drive an old school big red light in the panel for fuel pressure warning, as this is kinda important! (in addition to the G3X CAS message etc).


**Just as a thought experiment: this would work using a normal relay to turn the pump on or off using the fuel pump 2 switch as normal. The latching relay would get it's activate coil grounded from the low fuel pressure switch, and it's deactivate coil grounded from the fuel pump 2 switch selected in the on position. So in the event the pressure switch felt 20psi it would activate and ground the latching relay which would turn on the 2nd pump which would stay on. To turn it off, the latching relay deactivate coil grounded from the fuel pump 2 on switch (so selecting fuel pump 2 on, deactivates the latching relay, but activates the primary relay keeping the pump on, but resetting the latching relay circuit). I need to think more on this and make a diagram, as it would need some way to only be active once the primary pump is turned on - otherwise pump 2 would activate as soon as the engine busses were turned on.

 

[dmattmul]

Fuel valve plumbing

This is on the 14 with 90's on the suction (supply) and discharge (return) lines. I didn't want to use 90's on the suction but could not find another method. These reduce the margin of error needed when issues we don't take into consideration occur. (Dirty pre-filters as an example mentioned before)

To answer the OP yes both plumbing design and parts are similar. Most EFII users from what I've seen are using the Bus Manager and so we have an automatic back-up pump system that seems to work well. Yes, the Bus Manager is a SPOF but it does have a safety that bypasses the Bus Manager. It has been tested and appears to work ok. I'm ok with the risk. Every start-up tests (automatically) the auto switch over to insure both pumps are ok. SDS pump architecture is meant to use both pumps equally. The fuel flow is symmetrical whereas the EFII system is meant to use pump 1 as the primary as it flow is straight from the inlet through pump 1 to the outlet. (See pic) Using pump 2 the fuel goes a more serpentine route. (Yes, through what appears to be a banjo valve fitting) That's fine as pump 1 is meant to be your pump used 99% of the time. There is no reason why the SDS fuel pump design could not be used with EFII if you wanted to use both pumps equally or at the same time and forego an automatic switch over in times of stress and need.

 

[Mark33]

This is on the 14 with 90's on the suction (supply) and discharge (return) lines. I didn't want to use 90's on the suction but could not find another method. These reduce the margin of error needed when issues we don't take into consideration occur…….

I don’t think there’s a way to get around there being 90’s at the fuel selector….not to mention the path the fuel is actually having to go inside the selector itself.

 

[DanH]

So why is there any operational difference between the 2 with regard to how fuel makes it to the engine?

There isn't, not from tank to pumps.

I don’t think there’s a way to get around there being 90’s at the fuel selector….not to mention the path the fuel is actually having to go inside the selector itself.

It could be done, but perhaps not with a stock enclosure.

I went with 90's on this retrofit. Pulls through two of them. Heat is a big deal in the context of vapor formation. Here there's no opportunity for fuel heating between the tank and the fuel valve exit.

I might rig some clear tube and do a bubble check. Education and recreation.

Slightly off topic, but the dual pumps get a pre-filter, which needs to be cleaned from time to time. I arranged this one with a 1/4 turn valve. Close the valve, open the hose clamp on the filter, unscrew the B-nut at the selector (index finger) and the union downstream of the valve (at the screwdriver). The filter assembly can then be lifted out without dumping a lot of fuel in the cockpit. I expect a dribble from the pump inlet, but that's about it.
.

 

[TASEsq]

SDS pump architecture is meant to use both pumps equally. The fuel flow is symmetrical whereas the EFII system is meant to use pump 1 as the primary as it flow is straight from the inlet through pump 1 to the outlet. (See pic) Using pump 2 the fuel goes a more serpentine route. (Yes, through what appears to be a banjo valve fitting) That's fine as pump 1 is meant to be your pump used 99% of the time. There is no reason why the SDS fuel pump design could not be used with EFII if you wanted to use both pumps equally or at the same time and forego an automatic switch over in times of stress and need.

So in the SDS module, the fuel enters the anodised 'end cap' and presumably does a couple of 90 degree turns anyway before going into either of the pumps?

Whereas on the EFII system, the fuel flows straight through the primary pump. I can't really tell from your pic - where abouts is the banjo fitting? I can't really find a good image of the pump module online for EFII.

 

[Toobuilder]

Regarding the 90's in the SDS pump module inlet: The end cap is drilled to the OD of the NPT fitting all the way through so the cavity is significantly larger in diameter than the fuel line feeding it (and larger still than the pump inlets themselves). This has the effect of being a small "header tank" and reduces the velocity of the fuel turning the corner into the individual pump inlets. Yes, it is a geometric 90 degree turn, but at some point as you go up in size in the "header tank" the restriction of the 90 essentially disappears. Is the volume of the end cap cavity in the SDS module such that this restriction goes away completely - Don't know - but it is certainly less than a drilled 90 AN #6 fitting feeding it.

 

[dmattmul]

EFII Pump

So in the SDS module, the fuel enters the anodised 'end cap' and presumably does a couple of 90 degree turns anyway before going into either of the pumps?

Whereas on the EFII system, the fuel flows straight through the primary pump. I can't really tell from your pic - where abouts is the banjo fitting? I can't really find a good image of the pump module online for EFII.

Those that use SDS pumps can probably better comment but yes the fuel makes a couple 90's before going into the pump. It's also possible to use the 1/4 NPT's on the sides. It's been a awhile since I inspected my pump but the "banjo like" fitting is at the 90 where the fuel flows from the crossbar to pump 2 or the "b" pump.

As Dan mentioned it's possible to use temporarily clear tubing in the fuel rail to monitor for bubbles. I did this during some testing years ago. I still have the tubing with fittings, I might set up with a manometer and do some additional testing this time with 2 pumps running.

 

[Freemasm]

I am gland some of us now can read a pump curve. Useful data.

Point of clarity, if anyone cares, When talking pump curves, it is referring to a centrifugal pump. Keeping the operating point/range on the area of the curve with some decent slope is an important design consideration. Efficiency usually peaks around this point. Operation on the back side of the curve (high DP, low flow) can cause a unstable condition where the pressure can have wild swings; can also cause fluid flashing/cavitation. Too far out (high flow, low DP) can over-amp the motor and cause cavitation as well, though for different reasons.

Your probable near worthless knowledge for the day.

 

[rv6ejguy]

So in the SDS module, the fuel enters the anodised 'end cap' and presumably does a couple of 90 degree turns anyway before going into either of the pumps?

Whereas on the EFII system, the fuel flows straight through the primary pump. I can't really tell from your pic - where abouts is the banjo fitting? I can't really find a good image of the pump module online for EFII.

The SDS module has a passageway joining the pump inlets that is 5 times the area of the pump fitting ID so the turns present no restriction concern. Again, people are speculating about a problem which has clearly been shown not to exist in practice. We aren't the ones issuing a caution about using both pumps at the same time...

Many people have 90s on the fuel selectors in RVs with tunnels. Hard to avoid. We post the information for awareness of best practice here.

 

[TASEsq]

We aren't the ones issuing a caution about using both pumps at the same time...

Many people have 90s on the fuel selectors in RVs with tunnels. Hard to avoid. We post the information for awareness of best practice here.

Thanks Ross.

I appreciate your constant feedback on the forums here. It has helped me to understand how your product works.

I thought I had settled on EFII (basically because I liked the controller, no other real reason) but I’m considering both options more closely as a result of this discussion.

Is it the builders choice with your system to run a “fuel rail” from injector to injector or use the “fuel block” and lines to each injector? Are there pros and cons to each style of delivery? I could imagine the fuel in the lines from the fuel block to the injector could be subject to vaporisation like it can in the lines from the fuel spider to the injectors in a “normal” engine?

 

[airguy]

I could imagine the fuel in the lines from the fuel block to the injector could be subject to vaporisation like it can in the lines from the fuel spider to the injectors in a “normal” engine?

The fuel pump is putting out way more fuel than the engine can consume, the remainder gets swept right back through the backpressure regulating valve, the duplex fuel selector, and back to the tanks. There is no way the fuel is going to pick up enough heat in the short time it spends in the fuel block (or the rail, whichever is your choice) to begin vaporizing. The topside of the engine is the coolest environment FWF as well, with the incoming airstream there coming to the top of the cylinders. What heat it does pick up will be dumped into the fuel tank and lost through contact with the air through the tank skin.

 

[rv6ejguy]

Is it the builders choice with your system to run a “fuel rail” from injector to injector or use the “fuel block” and lines to each injector? Are there pros and cons to each style of delivery? I could imagine the fuel in the lines from the fuel block to the injector could be subject to vaporisation like it can in the lines from the fuel spider to the injectors in a “normal” engine?

No, we don't run rails as this is a mess on a Lycoming and in our view, a liability. You can PM or email me and I'll explain further.

The dead head, individual line to each injector layout we pioneered is well proven. Dave Anders has done hot starts (15 mins after shutdown) in 118F OATs. No issue.

With the top case mount fuel block, the block and lines are at ambient temperature in flight which is the most important regime.

The EFI uses much higher pressures than a Bendix type system. The fuel is under 45 psi after the pump so the boiling point is raised substantially. The AN3 lines have minimal volume. Hot starts are no issue.

With a fuel rail close to the exhaust ports and immersed in the hot cooling air coming down through the heads, the fuel will certainly pick up more heat here.

 

[airguy]

To back up Ross's statement about hot starts - I live in west Texas with our famous summertime heat, and I'm currently flying around 250-300 hours per year. Hot starts are NOT a problem with the SDS system, my engine doesn't care if it's hot, cold, or somewhere in between - it just works.

 

[Toobuilder]

Thanks Ross.

I appreciate your constant feedback on the forums here. It has helped me to understand how your product works.

I thought I had settled on EFII (basically because I liked the controller, no other real reason) but I’m considering both options more closely as a result of this discussion.

Is it the builders choice with your system to run a “fuel rail” from injector to injector or use the “fuel block” and lines to each injector? Are there pros and cons to each style of delivery? I could imagine the fuel in the lines from the fuel block to the injector could be subject to vaporisation like it can in the lines from the fuel spider to the injectors in a “normal” engine?

Aesthetic considerations should take a backseat to mechanical/engineering, IMHO. Despite the fact that neither system seems to be falling out of the sky, there are some compelling differences in even seemingly identical components between vendors. Do your homework. Make an informed decision.

Concerning the "Fuel rail" vs. "block" issue - I was an early adopter of the "direct fit" injector housings Ross invented and as result I had my own reservations about the amount of heat the lines would pick up. Against Ross' advice, I created a custom fuel rail type distribution system. It involves welded stainless steel tube and while it has performed perfectly to date, it is still a bit of a time bomb. Since the field experience now overwhelmingly shows the "block and hose" method SDS sells does not suffer from the fuel boiling/hot start issues, I will eventually go to that.

 

[[email protected]]

SDS fuel system design saves the day

Well, I for one was completely satisfied with the engineering that Ross and the boys have designed into the SDS EM-5F system I installed in my RV-6A 0-360 a couple of years ago.
I have had ZERO problems with their work and products EXCEPT!!!!!
I not recognizing the symptoms got myself into a corner of serious concern.
After about 70 hours on the system the pumps started intermittently making a loud whining noise when on the ground.
I thought there must be a check valve in the pumps rattling. The engine kept running and the fuel pressure remained steady.

After about another 15- ? hours it fully manifested the situation.
And they whined continuously when on the ground and in flight after gassing up 450 miles from home. Wake up call was ringing. Real loud.

Near the end of a three hour flight (50 miles out) to my home airpark the engine started dying, running rough, and reving really high then low, both pumps on didn't make any difference. I was over no mans land without an airport or field in sight.
I was at 8,500 feet so had the altitude to work it out.
After the high/low revs for about 3-5 minutes and all solutions exhausted, and I was still at 8,500' But, now down to 70 knots so as last resort I decided to reduce the throttle.
WaaLaa the engine proceeded to run smooth so I continued to my airport and landed uneventfully.
Well, except the adrenalin was still running.
The problem was quite literally plugged fuel filters, and that was after only 80 or so hours. Don't know where the extremely fine stuff came from, But, it was there. I pump my own Costco premium gas and it goes through a filter before it gets to the plane.
If you ever have your pumps start to WHINE Wake up and clean the filters or suffer the engine dying.
My luck varies But I used a lot that day. Art

 

[rocketman1988]

To back up Ross's statement about hot starts - I live in west Texas with our famous summertime heat, and I'm currently flying around 250-300 hours per year. Hot starts are NOT a problem with the SDS system, my engine doesn't care if it's hot, cold, or somewhere in between - it just works.

The same can be said for my EFII system...

 

[Walt]

To back up Ross's statement about hot starts - I live in west Texas with our famous summertime heat, and I'm currently flying around 250-300 hours per year. Hot starts are NOT a problem with the SDS system, my engine doesn't care if it's hot, cold, or somewhere in between - it just works.

The same can be said for my EFII system...

Same here, imagine that...

 

[rv6ejguy]

After about another 15- ? hours it fully manifested the situation.
And they whined continuously when on the ground and in flight after gassing up 450 miles from home. Wake up call was ringing. Real loud.


The problem was quite literally plugged fuel filters, and that was after only 80 or so hours. Don't know where the extremely fine stuff came from, But, it was there. I pump my own Costco premium gas and it goes through a filter before it gets to the plane.
If you ever have your pumps start to WHINE Wake up and clean the filters or suffer the engine dying.
My luck varies But I used a lot that day. Art

Appreciate your post Art. Your report make 4 similar incidents that I know of now.

As Art says, take this seriously. It's important.

One reason we recommend 40 micron filters rather than 10 as others do as that they will plug more slowly and give more warning of a critical situation. 40 gives sufficient protection for the pump and injectors and offer lower restriction than 10 micron elements.

I'll be issuing a SB on this later this week so people are more aware.

The pumps are telling you something if they are noisy. Listen to them. Check or replace the filters.

 

[TASEsq]

With the top case mount fuel block, the block and lines are at ambient temperature in flight which is the most important regime.

The EFI uses much higher pressures than a Bendix type system. The fuel is under 45 psi after the pump so the boiling point is raised substantially. The AN3 lines have minimal volume. Hot starts are no issue.

With a fuel rail close to the exhaust ports and immersed in the hot cooling air coming down through the heads, the fuel will certainly pick up more heat here.

I was thinking more of in a parked situation. With the fuel block, the fuel between the block and the injectors is sitting getting all the rising heat from the engine below it. The typical problem with a Bendix system and the fuel spider. With a fuel rail this hot fuel is pushed back to the tank as soon as the pumps are on. I had it explained to me these systems are high pressure and not the same as the bendix at all, and that any vapors in the lines between the fuel block and injectors are just mixed with cold fuel and/or sucked through the injectors on start anyway. As you’ve said, obviously operational experience shows it’s not a problem. Was just wondering. The EFII fuel rail under the cylinder obviously also works.

I notice the SDS system uses ports on top of the engine but EFII uses ports at the bottom? Does anyone know whether the location of the injectors makes any difference? (Again they obviously both work well).

Aesthetic considerations should take a backseat to mechanical/engineering, IMHO.

You are right!! The EFII controller is a lot neater in my opinion but if the SDS system is better for my use then it will be the one to go with (or not).

Despite the fact that neither system seems to be falling out of the sky, there are some compelling differences in even seemingly identical components between vendors. Do your homework. Make an informed decision.

Yeah and it is hard to get much info on either system in detail really!! There is a lot of “unlike the other vendor our system…” from both vendors - which is confusing for new blokes and honestly unhelpful from both sides. Builders seem to pick a side like it’s a religion somewhat! (I’ve appreciated in this thread how helpful and unbiased all the info has been). Both vendors are a little secretive in some ways and both their manuals are not designed for bog cold newbies like me - they are both very daunting!! But threads like this are really helping me understand and I’m becoming more and more comfortable I can do this myself.

So far the main differences I can understand are:
1. Cockpit controller different (SDS has an external mixture knob)
2. EFII LOP is automatic but SDS is a button
3. SDS fuel pump module is maybe better than EFII in my opinion and doesn’t have a limitation of 1 pump for takeoff (this may be due to the banjo fitting rather than the “header area” in the SDS pump housing?).
4. SDS uses and block and lines instead of a fuel rail like EFII
5. SDS is fuel above the cylinders whereas EFII is below - both systems work it seems despite claims by both vendors the other system is no good!
6. EFII has a bus manager which most people seem to be using. This is a SPOF in my opinion. If I go EFII I probably won’t use it.
7. The ignition systems seem similar however SDS seems to have seperate power and ground returns for each injector separately. EFII seems like a common ground for injectors which is a SPOF possibly?
8. I’m not sure if there are differences in the injectors between the vendors?
9. EFII uses a 90 micron filter before the pumps and a 10 micron after, whereas SDS uses 40 micron before and another 40 micron after. I guess the smaller 10 micron one is due to differences in the fuel injectors themselves?

One reason we recommend 40 micron filters rather than 10 as others do as that they will plug more slowly and give more warning of a critical situation. 40 gives sufficient protection for the pump and injectors and offer lower restriction than 10 micron elements.

Thanks Ross,

I was thinking of using the TS Flitelines wing root filter kit (which I believe are 40 micron). Mostly because in the -14 with the power module installed getting in the tunnel is no small task. For forward of the pumps can the additional fuel filter be placed on the firewall to make servicing easier? I can’t imagine at 45 psi the location or orientation matters?

The problem was quite literally plugged fuel filters, and that was after only 80 or so hours. Don't know where the extremely fine stuff came from, But, it was there. I pump my own Costco premium gas and it goes through a filter before it gets to the plane.
If you ever have your pumps start to WHINE Wake up and clean the filters or suffer the engine dying.
My luck varies But I used a lot that day. Art

Hi Art,

Did you ever work out what was the source of the “fine stuff” was? Construction debris?

Can you share some details of your filters? What size did you have installed and where were they located?


———————
There has been 1 respondent on the poll only who seems to be using EFII without the bus manager (if that person doesn’t mind sending me a PM I would love to touch base).

Thanks once again for everyone’s help! I’m learning stacks which is helping my decision making. Hopefully the thread can help others in the future too. I understand there are 2 distinct camps here but I think this is a great balanced thread so far! Thanks to all who have made an input.

 

[DanH]

I was thinking more of in a parked situation. With the fuel block, the fuel between the block and the injectors is sitting getting all the rising heat from the engine below it. The typical problem with a Bendix system and the fuel spider.

Trent, for the most part it's equally hot inside the lower cowl.

Parked EFI and constant flow are not at all similar. The Bendix boils the fuel in the spider lines a few moments after shutdown. Since constant flow nozzles are basically open holes, boiling pushes most of the fuel into the intake ports, which floods the engine rich as six feet up a bull's butt. However, leave it parked long enough, and most of the dumped fuel evaporates, after which, if your procedure assumes a rich condition, it won't start.

An EFI injector pintle is closed when not energized. The lines can get hot, but no fuel can enter the engine unless the injector is defective. And at 40 psi, avgas would need about 240 F to boil.

2. EFII LOP is automatic but SDS is a button

The "automatic" claim is puffery. It merely means the system can be programmed to be rich at high power and go lean when the power is pulled to some given MP/RPM. Either system can be set up that way.

Both have a mixture knob so mixture can be varied from the programmed values. The SDS button is simply a one-touch way to vary a pre-established amount. Neither operates as a closed loop system.

 

[TASEsq]

…which floods the engine rich as six feet up a bull's butt.

I’m not a country boy, but that sounds pretty rich!

Thanks for your feedback. Either system seems to work pretty much the same - doesn’t sound like the fuel rail versus the block and lines method really changes how effective or safe the system is.

The SDS manual gives pretty straight forward instructions for installing the injectors into the injector ports on top of the engine. However, the EFII manual is pretty lean - all it says is install in primer ports without any real instruction. Is the installation of the injectors any challenge? (I will be doing it on an in-390).

 

[dmattmul]

EFI group help

Well, I for one was completely satisfied with the engineering that Ross and the boys have designed into the SDS EM-5F system I installed in my RV-6A 0-360 a couple of years ago.
I have had ZERO problems with their work and products EXCEPT!!!!!
I not recognizing the symptoms got myself into a corner of serious concern.
After about 70 hours on the system the pumps started intermittently making a loud whining noise when on the ground.
I thought there must be a check valve in the pumps rattling. The engine kept running and the fuel pressure remained steady.

After about another 15- ? hours it fully manifested the situation.
And they whined continuously when on the ground and in flight after gassing up 450 miles from home. Wake up call was ringing. Real loud.

Near the end of a three hour flight (50 miles out) to my home airpark the engine started dying, running rough, and reving really high then low, both pumps on didn't make any difference. I was over no mans land without an airport or field in sight.
I was at 8,500 feet so had the altitude to work it out.
After the high/low revs for about 3-5 minutes and all solutions exhausted, and I was still at 8,500' But, now down to 70 knots so as last resort I decided to reduce the throttle.
WaaLaa the engine proceeded to run smooth so I continued to my airport and landed uneventfully.
Well, except the adrenalin was still running.
The problem was quite literally plugged fuel filters, and that was after only 80 or so hours. Don't know where the extremely fine stuff came from, But, it was there. I pump my own Costco premium gas and it goes through a filter before it gets to the plane.
If you ever have your pumps start to WHINE Wake up and clean the filters or suffer the engine dying.
My luck varies But I used a lot that day. Art

Art, thanks for sharing and it’s a valuable lesson for everyone. It’s bound to occur to any of us. Contaminated fuel can occur anywhere. I know you said the pump sounded different and you said your FP looked ok initially. Can you give us more details when the engine started running rough. FP looked ok? How about change in EGT? Did you try and richen the engine ? I understand there’s a lot going on during this “event” but maybe after you’ve landed your EFIS had data to share? Obviously reducing MP reduces fuel flow and that helped the mixture conditions given fuel was “reduced”. Besides listening to the fuel pump whine (and change filters) if we get this condition in flight any recommendations for in flight corrections ?

Thanks again for documenting this.

 

[KatanaPilot]

Neither operates as a closed loop system.

Coming soon to an SDS equipped airplane - closed loop operation (EM-6).

I’m not a country boy, but that sounds pretty rich!

Thanks for your feedback. Either system seems to work pretty much the same - doesn’t sound like the fuel rail versus the block and lines method really changes how effective or safe the system is.

The SDS manual gives pretty straight forward instructions for installing the injectors into the injector ports on top of the engine. However, the EFII manual is pretty lean - all it says is install in primer ports without any real instruction. Is the installation of the injectors any challenge? (I will be doing it on an in-390).

If you can build an airplane, you can install SDS. My suggestion is to take a good look at the quality of the hardware (throttle body, coil pack mounts, etc.) and compare SDS to FlyEFII. I think your decision which system to buy will be easier if you do that. Personally, I think the injector port installation is cleaner than the primer port. Picture below is my IO-540 (PV) installation. Used TS/AS Flightlines versus the SDS supplied fuel lines because Tom was able to do the lines in blue Integral firesleeved fuel supply and return lines also from Tom.

 

[sbalmos]

I like to watch threads from the sidelines. But I'll chime in, for what it's worth. Krea, your install is nice. And I agree the SDS system is perfectly capable. I will never hold a match to Ross's posts here. Nor DanH. Personally (and I do mean personally), I think having routed on top of the engine is a cluttered PITA. I'm actually surprised that, in some way, it doesn't affect engine cooling. It's certainly a lot more outer baffle or inter-cylinder baffle penetrations (read: more points for air leakage). I have nothing to prove that, it just /looks/ like it would.

I'm posting the one recent pic I can find quickly from this past winter of my engine. Please avert your eyes from the ugly yellow - it's off an old Citabria. I started my build and flying with the original EFII system, then retrofitted to System32 after about two years of flying. There's no issue with installing the primer port-based injectors. I have the MP sensors on a clamped mounting plate because I started running out of accessible firewall space during the original EFII to System32 retrofit. The oxygen sensor controller is hanging loose here during my annual CI, but it's normally mounted to the upper engine mount leg, where the two wraps of electrical tape are.

Controller/software-wise, the one thing that really stands out to me between the two now is the ability to change all the mappings through a set of CSV files you put on an SD card loaded through the System32 controller head. No need to click through the 250 RPM increments or MP increments in the SDS/old-EFII control head. And in the CSV files you can have any RPM increment and MP granularity for any step. I haven't gone that far with my mappings, but it is a capability difference to note if you're of that level of tweaking abilities.

I can't remember whether SDS / old EFII was capable of this, but there's also the automatic "accelerator pump emulation" that injects more fuel at more sudden up-throttling at lower RPMs to prevent engine stumbling. I mention that since it's a fairly common trick to emulate pre-start priming. That's my cold start sequence - two pumps of the throttle to have the AP function squirt a bit of fuel in, separated by 10 seconds between them. 5 seconds after the second prime, hit The Big Red Button, 2 blades of cranking, and I'm running.

Honestly, I'm not sure what the hangup is over running one pump or two. Clearly both systems and their pump manifolds have more than enough flow to ensure quick starting even with heat soaking.

At some point you have to ask yourself "does this difference really mean anything functionally /to me/? does it /really/ matter, and how?"

 

[TASEsq]

Honestly, I'm not sure what the hangup is over running one pump or two. Clearly both systems and their pump manifolds have more than enough flow to ensure quick starting even with heat soaking.

At some point you have to ask yourself "does this difference really mean anything functionally /to me/? does it /really/ matter, and how?"

Thanks for chiming in!

The issue I have with one pump is on takeoff - should that pump fail / cb pop etc then the engine stops too! There’s a perfectly good second pump sitting unused. The bus manager provides a solution of course - but I just can’t get past a single box running everything.

 

[sbalmos]

Fair enough. Though I don't think I've heard of such an event happening - neither a pump failure on takeoff, nor a Bus Manager failure. As a point of reminder, the Bus Manager selector circuit isn't directly powering the pumps, it's driving a separate power relay - a relay that's normally-closed, and thus powering pump 1. A single box "runs everything" - but that failure mode defaults back to primary operation mode, not angry-pixies-stop-flowing.

Has Robert ever had reports of a pump failure on takeoff? Or a Bus Manager pump selector circuit failure?

We're hanging a major platform choice here on what-if scenarios that, in my mind, I wonder what the /practical probability/ of them occurring is.

As a random Option C idea, does Ross sell his pump manifold assembly separately? Install a System32 with SDS pumps?

 

[airguy]

Neither operates as a closed loop system.

YET.

The EM-6 which SDS is about to release does have that capability.

I can't remember whether SDS / old EFII was capable of this, but there's also the automatic "accelerator pump emulation" that injects more fuel at more sudden up-throttling at lower RPMs to prevent engine stumbling. I mention that since it's a fairly common trick to emulate pre-start priming. That's my cold start sequence - two pumps of the throttle to have the AP function squirt a bit of fuel in, separated by 10 seconds between them. 5 seconds after the second prime, hit The Big Red Button, 2 blades of cranking, and I'm running.

Yes, SDS has the accelerator pump function, and you can adjust how much additional fuel you want it to deliver. It monitors the throttle position and will inject extra fuel for a rapid opening movement.

 

[rv6ejguy]

I notice the SDS system uses ports on top of the engine but EFII uses ports at the bottom? Does anyone know whether the location of the injectors makes any difference? (Again they obviously both work well).


Yeah and it is hard to get much info on either system in detail really!!

So far the main differences I can understand are:
1. Cockpit controller different (SDS has an external mixture knob)
2. EFII LOP is automatic but SDS is a button
3. SDS fuel pump module is maybe better than EFII in my opinion and doesn’t have a limitation of 1 pump for takeoff (this may be due to the banjo fitting rather than the “header area” in the SDS pump housing?).
4. SDS uses and block and lines instead of a fuel rail like EFII
5. SDS is fuel above the cylinders whereas EFII is below - both systems work it seems despite claims by both vendors the other system is no good!
6. EFII has a bus manager which most people seem to be using. This is a SPOF in my opinion. If I go EFII I probably won’t use it.
7. The ignition systems seem similar however SDS seems to have seperate power and ground returns for each injector separately. EFII seems like a common ground for injectors which is a SPOF possibly?
8. I’m not sure if there are differences in the injectors between the vendors?
9. EFII uses a 90 micron filter before the pumps and a 10 micron after, whereas SDS uses 40 micron before and another 40 micron after. I guess the smaller 10 micron one is due to differences in the fuel injectors themselves?

We put the injector where the Lycoming factory puts it. On top results in lower temps for the injector and fuel in flight which is the most important condition. It's not subject to the hot air coming off the cooling fins or the IR off the adjacent exhaust pipes. Our setup hasn't suffered any fuel fires to date...

Happy to discuss any questions you have about SDS by email which might not clear from the documentation. We are writing new manuals for the EM-6 right now.

The mixture knob is a backup safety device on SDS. Allows a quick manual override of mixture if something was to go amiss. It saved the day in a couple instances.

We prefer to leave the pilot in control of LOP operation.

I'd look at the execution/ hardware of the injector mounting and draw your own conclusions. PM or email me if you'd like more information.

We use different injectors with metal body and a narrow spray pattern so the cone doesn't impinge on the bore of the mount.

In our 29 year experience, manufacturing/ selling over 10,000 controllers we feel 40 micron filters are the best compromise between pump/ injector protection and resistance to plugging with debris.

 

[rv6ejguy]

I'm actually surprised that, in some way, it doesn't affect engine cooling. It's certainly a lot more outer baffle or inter-cylinder baffle penetrations (read: more points for air leakage). I have nothing to prove that, it just /looks/ like it would.

I can't remember whether SDS / old EFII was capable of this, but there's also the automatic "accelerator pump emulation" that injects more fuel at more sudden up-throttling at lower RPMs to prevent engine stumbling.

Sealed penetrations for fuel lines if you use the baffle mount fuel block option (the block face seals the holes in the baffle so zero leakage).

Not sure why you'd think that injector lines above the cylinders would affect cooling? The area involved is minute compared to the area above the cylinders vs the area of the cooling inlets. Doesn't seem to have affected the cooling on 3 Sport Class Gold race champions at Reno pushing 800hp...

Accel pump feature has been part of SDS since the EM-1 in 1994. We also pioneered the pump to prime software for Lycomings back in 2015.

 

[DanH]

The EM-6 which SDS is about to release does have that capability (closed loop)

I know...and you'll be an early adopter because, IIRC, you run a lot of car gas. However, until we have fleetwide access to unleaded avgas, the typical SDS or EFII user will be running open loop regardless of model.

 

[airguy]

I know...and you'll be an early adopter because, IIRC, you run a lot of car gas. However, until we have fleetwide access to unleaded avgas, the typical SDS or EFII user will be running open loop regardless of model.

I should have my EM-6 in a couple weeks to begin testing.

 

[[email protected]]

In response to dmattmul
When the pump first started whining once in a while I was thinking that it was weird, But, it went away after a short burst on the ground, never in the air.
Fuel pressures and egt and cht always looking normal. I have an HDX with full monitoring. UNTIL the problem fully came to the fore front. Then the fuel pressures and RPM shot up and down like a yo yo and I knew I had a fuel delivery not electrical problem.
I take off with one pump and fly with one pump. This type of pump is a very proven design and can go millions of gallons with out a hiccup.
In other words, I was all dumb fat and happy till WHAM I wasn't.
AS far as when the engine started running rough. It actually didn't run rough just surging high and low, torqueing the airplane up and down. In about a 3 second interval.
I enriched mixture, leaned, turned pumps on and off. even turned both off and let the engine quit running. turned everything off and on etc etc etc.
I will say adrenalin was running But I have been in some pretty tight/bad situations so am actually pretty calm during HIGH stress situations.
I was still flying, albeit weirdly, so no real death alert upcoming.
If you get this flight condition I am sure you will not have cleaned the filters. so you won't get this if you clean the filters.
I was given a warning a dozen times, I just didn't recognize the problem.
The crux is I have been a mechanic since I turned 14 1/2 because that's when I got my first 1956 Chev from under a cherry tree for $50.00
It had a rod start hammering when my brother drove it home. Dad says If you're gonna drive them you have to learn how to fix them. Here is a box of tools. Go at it. Since then I have worked on literally thousands of rigs.
As far as a way to prevent this.
If you hear an unusual whine from the pumps CLEAN YOUR FILTERS. It only takes 30 minutes or so. Then you won't get this condition in flight.
My luck varies Art

 

[rv6ejguy]

I know...and you'll be an early adopter because, IIRC, you run a lot of car gas. However, until we have fleetwide access to unleaded avgas, the typical SDS or EFII user will be running open loop regardless of model.

We've had closed loop control since 1995 however this generally targeted stoichiometric so wasn't suitable for aviation use unless you wanted to run at peak EGT. We did flight test it using a wideband with a new target of 13 AFR back in 2008 in Florida on an RV-10. Worked well.

The EM-6 expands and refines this capability with user programmable AFR targets for each 100 rpm range.

We now also have separate cylinder trim amounts for both best power and LOP schedules.

 

[TASEsq]

Fair enough. Though I don't think I've heard of such an event happening - neither a pump failure on takeoff, nor a Bus Manager failure. As a point of reminder, the Bus Manager selector circuit isn't directly powering the pumps, it's driving a separate power relay - a relay that's normally-closed, and thus powering pump 1. A single box "runs everything" - but that failure mode defaults back to primary operation mode, not angry-pixies-stop-flowing.

I have no idea about the pump (but it’s a common car pump so likely very reliable) and Robert says no bus manager failures ever. Where do you get the info about the bus manager? (How it works internally). The relay functionality sounds similar to how I would plan to wire my pumps anyway. But again, being all in one enclosure doesn’t sit well with me from a SPOF perspective. Maybe I’m not understanding how electronics fail etc. In my mind though, a small fire in that box could kill the engine and all the aircraft power in one go. Is this a unrealistic fear? (Maybe!) it’s the same reason I can’t come to grips with the vpx etc. I fly an electronic aircraft for a living and boxes fail all the time.

I imagine a pump failure after takeoff wouldn’t be the pump actually failing but could be a blocked filter, pooped cb, chafed wire, bad electrical design etc. Point is there’s a perfectly good pump next to it which if off! Why can’t it be on?

As a random Option C idea, does Ross sell his pump manifold assembly separately? Install a System32 with SDS pumps?

I wondered that too but was afraid to ask! Having said that, the only real difference is the header area on the SDS pimps versus a banjo fitting on the second pump. Perhaps the banjo fitting is the cause of Robert’s concerns on cavitation etc on the suction side? Who knows.

Happy to discuss any questions you have about SDS by email which might not clear from the documentation. We are writing new manuals for the EM-6 right now.

I'd look at the execution/ hardware of the injector mounting and draw your own conclusions. PM or email me if you'd like more information.

In our 29 year experience, manufacturing/ selling over 10,000 controllers we feel 40 micron filters are the best compromise between pump/ injector protection and resistance to plugging with debris.

Thank you once again for all your input Ross. It’s great having you online here.

Can the post filter be on the firewall with no issues?

I know...and you'll be an early adopter because, IIRC, you run a lot of car gas. However, until we have fleetwide access to unleaded avgas, the typical SDS or EFII user will be running open loop regardless of model.

Is this because the leaded fuel kills the oxygen sensor?

 

[dmattmul]

Thanks Art

Sounds like you handled it well. I’m assuming your pre-filter plugged and sounds like Ross might have more data on other filters that have clogged or partially clogged. I’m guessing all would be the pre-filter as it’s impossible to pull more than 14.7 delta across the media whereas the post filter can go up to 100 psi ? delta across the media. I’ve got in the habit of running my pumps and engine start sequence with my ANR headsets off so I can listen to the pumps and oil pressure chime I have. With the headsets on it’s hard to hear any issues and once the motor starts impossible for me. Since some can run 2 pumps it “seems” that a partially clogged pre-filter would become more apparent since the flows are basically double and bound to be more cavitation running 2 pumps if a pre filter was beginning to clog? Would this indicate earlier if there was a problem? A clogged filter is every pilots nightmare but it could occur any time with one bad tank of gas. I sump my tanks every flight and pour the contents through qualitative filter paper and surprised at the amount of particles I collect. Again thanks for the input.

 

[riseric]

Trent,
On FlyEFII's web site, there's a download tab and towards the bottom, you will find the Bus Manager installation document.
It's detailled and it shows the circuitry inside. Study that.

I for one, would not fly without it.
Amongst other functions, it distributes the power from one or two batteries to an essential bus and a general bus. It's connected directly to the batteries from the hot side of the main battery contactor(s).
There's an Emergency switch to bypass the Bus if the internals fail so the batteries continue supplying the buses.
In fact, if you switch on the Emergency switch while the Key switch AND the battery contactor are OFF, the pump turns ON and as well everything connected on the Essential Bus for that matter.
As for the pump(s), the Bus Manager monitors the fuel pressure, if it drops to 25 psi or less (you adjust the trip point), it turns on the #2 pump so instantly that you can't notice the difference.
Helpful and essential on takeoff... no need to manually switch #2.
Read the document, it should help you understand the system, and that's very important, whaterver system you choose...

 

[TASEsq]

Trent,
On FlyEFII's web site, there's a download tab and towards the bottom, you will find the Bus Manager installation document.
It's detailled and it shows the circuitry inside. Study that.

Thank you - I have had a quick read of that document before - will see if I can get some deeper understanding second time round.

 

[airguy]

Is this because the leaded fuel kills the oxygen sensor?

Correct, current oxygen sensors don't like 100LL. I have seen some run 200 hours of 100LL exposure, and had one fail at 15 hours, but most of them are in the 50-75 hour range when running 100LL, at least the way I run my engine. I keep a spare on my work bench at all times, replace it when it dies and order a new spare.

 

[rv6ejguy]

I have no idea about the pump (but it’s a common car pump so likely very reliable)Maybe I’m not understanding how electronics fail etc. In my mind though, a small fire in that box could kill the engine and all the aircraft power in one go. Is this a unrealistic fear?

I imagine a pump failure after takeoff wouldn’t be the pump actually failing but could be a blocked filter, pooped cb, chafed wire, bad electrical design etc. Point is there’s a perfectly good pump next to it which if off! Why can’t it be on?

I wondered that too but was afraid to ask! Having said that, the only real difference is the header area on the SDS pimps versus a banjo fitting on the second pump. Perhaps the banjo fitting is the cause of Robert’s concerns on cavitation etc on the suction side? Who knows.

Can the post filter be on the firewall with no issues?

Is this because the leaded fuel kills the oxygen sensor?

When you've produced over 10,000 controllers in almost 30 years, turned them loose on the public and accumulated an estimated 23 million hours collectively on the fleet, you'll eventually see some interesting things.

I put a lot more weight on historical experience- demonstrated MTF rather than something like FMEA which just asks what if? There are so many single points of failure on single engined aircraft that if you did an FMEA on it, you'd have a long list and maybe wouldn't fly at all.

So here is a photo of the worst "fire" we've seen in an ECU (EM-4).
Obviously very high current flowed through this component for a long time to cause this type of damage indicating an unfused component somewhere along the line, most likely the ECU power lead where we recommend 2 amps max. Usually once the trace burns up and things go open, the heating stops. If this ECU was actually fused with 2 amps, this damage could never have happened.

We've seen people inject 400V from an MSD into the wrong place and fry things too but that won't happen on Lycoming setup where there is no MSD.

I've only seen one legit and unexplained failure to date on an aircraft ECU and that was on Greg's 9A. He arrived back safely on the B ECU. This appeared to be a simple component failure on something rated at 200V. Normally these parts are very robust and never fail but with enough hours on almost anything, you are bound to eventually see a failure.

Have seen 2 other separate failures traced to the av tech installer wrapping the IAT and CHT sensor cables around the plug wires for a couple feet. Obviously you'd never want to do this. Inductance and capacitance coupling can do bad things when you have pulsing 30KV an 1/8th of an inch away from sensor input wires. He came back to base on the B ECU as well.

We're approaching a million flight hours on the SDS aviation fleet now, nobody has had a fire on a board, shutting down both yet. The risk would appear from this data to be very small if fused as recommended.

We have seen pumps fail for no apparent reason- even upon disassembly. A good reason to have 2. As I mentioned, we've heard of 6-7 failing to date and several more being damaged by partially plugged filters and having to be replaced.

I'm not sure that anyone has established that the Brand X pump modules have any issue. Why doesn't someone just test it and report back here? Don't theorize, simply run the experiment and see if the concern is valid. Speculation without facts is useless.

Yes, we usually recommend mounting the post filter FWF. Easy to access there and won't drip inside the airplane when you check/ service it.

Correct, as Greg said above, closed loop hasn't been implemented on 100LL burning aviation engines because sensor life is nowhere near what it is in the automotive world- say around 5000 hours. We have seen failures in as little as 2 hours though the high time user has almost 650 hours on his sensor. Quite a range.

I see a trend here in this thread where people surmise a problem with no apparent data to make the concern a valid one. I suggest folks evaluate what is being said and WHY. Is the advice based on hearsay or factual history of a problem? Is it just marketing or idle conjecture?

One of the main reasons I post here is to answer questions about our products as we have hundreds of customers here on VAF. I hope my answers hold up to technical and factual scrutiny. We try to turn out the most durable and reliable bits that we can. I personally fly what we sell. We replace parts that show issues in the field and we issue SBs to alert users of things to check and look out for. User feedback is most important to us in this regard for product improvement and safety. Denial of failures is dangerous in aviation. If I see a couple of similar failures from customer reports, we'll usually issue an SB or guidance and come up with a fix and some new parts if applicable.

An aviation supplier who has been around for 5-10+ years without having any problems would be pretty rare. If they never issue a service instruction, guidance, bulletin or AD, either they have an exceptional product or there could be another explanation.

 

[TASEsq]

Thanks Ross for the detailed post.

So here is a photo of the worst "fire" we've seen in an ECU

We're approaching a million flight hours on the SDS aviation fleet now, nobody has had a fire on a board, shutting down both yet. The risk would appear from this data to be very small if fused as recommended.

I was referring to the EFII Bus Manager here but you are right - I need to spend some time to figure out how that works to decide if there really is a SPOF risk using it before I “count it out”. With regard to your dual ECU in one box - I agree with your operational experience that a ‘fire’ or short in one board is unlikely to take out the other board. Appreciate your honesty with showing us the failures. Information is power (and in this case confidence in the system for potential customers). I initially thought the EFII having 2 ecu’s in seperate boxes was an advantage but I see now, based on operational experience, it isn’t a real concern.

We have seen pumps fail for no apparent reason- even upon disassembly. A good reason to have 2. As I mentioned, we've heard of 6-7 failing to date and several more being damaged by partially plugged filters and having to be replaced.

Yeah I really think having 2 running for takeoff is a priority for me for this reason. Or an auto-switching functionality if this isn’t possible.

I'm not sure that anyone has established that the Brand X pump modules have any issue. Why doesn't someone just test it and report back here? Don't theorize, simply run the experiment and see if the concern is valid. Speculation without facts is useless.

I see a trend here in this thread where people surmise a problem with no apparent data to make the concern a valid one. I suggest folks evaluate what is being said and WHY. Is the advice based hearsay or factual history of a problem? Is it just marketing or idle conjecture?

And this was the main reason for starting this thread in the beginning. I was told by the vendor that their pumps cannot be run in a particular way with a theoretical reason why not. If there were real world incidents etc then that’s a different story. But it’s hard to just accept a “this may happen” scenario, so I thought I would see what the brains trust said. Turns out there is no one who is running 2 pumps for takeoff and I assume it’s based on the vendor advice. But the why is me is strong! Perhaps if everyone ran 2 we would find it’s not an issue, and the main selling point for the bus manager is moot. Or perhaps not! Who knows, as you say, without a real world test.

 

[rv6ejguy]

Trent, I thank you for starting this thread. It's been valuable to explore certain elements of EFI and we see some user reports which we didn't know about before (not everyone reports problems to us).

This has helped to educate everyone, including ourselves.

 

[airguy]

Back to the original question for a moment.

There are only a couple negatives I can see to running both pumps at once - the possibility of increased flow causing cavitation, and running excessively rich.

With hydraulically correct fuel system design (which is woefully lacking, IMHO, in our experimental aircraft field) we can eliminate the first problem of bubble formation in the fuel system.

The second issue of running rich can be avoided by adjusting the mixture control in the cockpit but cannot be avoided, strictly speaking. Both SDS and EFII systems fire the injectors based simply on dwell time - how many milliseconds open versus closed. They have no way to know how much fuel is passing through them, only how long they should be open. If the fuel pressure delta across the injector face is not constant, then neither is the fuel quantity. When you run two pumps, the downstream fuel pressure will be higher and more fuel will be move through the injector for the same dwell-time, resulting in a richer mixture.

Now - to Ross's point - my personal testing and experience has shown me this is NOT a real problem, though you can see it happening with the engine instrumentation. It does run richer - but not enough richer to be a problem, so let's not get into the prayer beads just yet worrying about that one. I usually take off with my AFR set in high 12's region for a single pump with fuel pressure at 44, and when both pumps are on the fuel pressure comes up to 50 and my AFR will go low-to-mid 12 regions, still quite acceptable for a takeoff power setting. If it makes you feel more comfortable to operate two pumps for takeoff/landing, AND you have a hydraulically correct inlet setup to avoid vapor bubbles, then go for it.

The one thing you DON'T want to do is to run both pumps trying to avoid a POTENTIAL problem of pump failure, and introduce a REAL problem of pump cavitation and vapor lock because you are drawing too much fuel flow through a poor inlet plumbing installation. You could end up causing your own loss of power rather than avoiding it. MAKE CERTAIN you can run both pumps without vapor bubble formation before you do it. Keep the pressure loss upstream of the pumps as low as possible and let them breathe all the fuel they want. That means clean (and large) filtration, lack of drilled 90's, no restrictions.

TEST TEST TEST - every installation is different. The only way to know for sure is to test your installation.

 

[Mark33]

…….(snip)…..When you run two pumps, the downstream fuel pressure will be higher and more fuel will be move through the injector for the same dwell-time, resulting in a richer mixture…….

Greg,
If the fuel pressure regulator is working properly, how can this be?

 

[rv6ejguy]

Greg,
If the fuel pressure regulator is working properly, how can this be?

The FPR has about a .200 orifice. Once the valve is fully open and you try to pass more volume through it, pressure must rise.

Flow at the injector varies as the square root of the pressure so a rise of 5 psi doesn't have so much effect on AFR. Should be around a 5% change in AFR.

 

[Mark33]

The FPR has about a .200 orifice. Once the valve is fully open and you try to pass more volume through it, pressure must rise.

Flow at the injector varies as the square root of the pressure so a rise of 5 psi doesn't have so much effect on AFR. Should be around a 5% change in AFR.

Roger that. I was thinking that the regulator could bleed off as much extra fuel as you could through at it so as not to raise pressure.

 

[DanH]

I usually take off with my AFR set in high 12's region for a single pump with fuel pressure at 44, and when both pumps are on the fuel pressure comes up to 50 ....

Close to 100 posts about one pump vs two, and finally we hear the fuel rail won't maintain set pressure with two pumps running?

The FPR has about a .200 orifice. Once the valve is fully open and you try to pass more volume through it, pressure must rise.

Flow at the injector varies as the square root of the pressure so a rise of 5 psi doesn't have so much effect on AFR. Should be around a 5% change in AFR.

Any notion about the perfect accuracy of EFI just got shot in the ***.

 

[Mark33]

Close to 100 posts about one pump vs two, and finally we hear the fuel rail won't maintain set pressure with two pumps running?



Any notion about the perfect accuracy of EFI just got shot in the ***.

So even though it doesn’t account for “much” of a rise in fuel rail pressure when running two pumps VS. one, to get everything dialed in perfectly, would a different/larger volume fuel pressure regulator be the answer? Although we’re only talking about a small difference in rail pressure when comparing the two scenarios and any increases in “richness” can easily be reduced with the mixture knob if needed. I think most of this discussion and pointing out the differences has mostly just talking points….but possibly worthy talking points all the same.

 

[airguy]

Fuel backpressure regulators can be had in any size you want, just source a bigger one. The Borla regulator that Ross uses is well sized for its mission, I don't know what Robert uses.

Any notion about the perfect accuracy of EFI just got shot in the ***.

Right. And carbs never have any problems either.

 

[DanH]

The Borla regulator that Ross uses is well sized for its mission...

Let's stick to facts. You're reporting your system goes rich with two pumps running. So, detail it. What size are your return lines, and are you using the SDS pump module or individual wing root pumps?