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Engine problem, help needed

bifft

Well Known Member
Clear back in July, after 21 years building, had my first flight. Wrote it up here:

http://user.xmission.com/~bifft/rv/first.htm

On this flight, I did a stall test, and after that the engine wouldn't develop full power. Flew right back and landed. Trying to troubleshoot the problem, found that there was some junk in the throttle body's last chance filter. Thought that this was the cause of the problem. Rotec recommends a 40micron fuel filter, all I had was Van's gascolator.

I suspect I put the dirt into the system when I drained the tanks to fix some leaks. I drained into my old 5 gallon tanks I have used for chainsaw gas, off road trips, etc. Dirt probably came out of there.

So, added a 10 micron fuel filter, cleaned out the lines, flew again. Had the exact same problem. Takeoff and climb out are fine. Slow down to do a stall test, engine won't go back to full power. Can only run below 2000 rpm or so. Fortunately this is plenty to fly back to the airport and land. Inspection found only a few specks in the throttle body filter, a bit more in the larger filter.

Monday went back and flushed out the fuel system. Got a filter funnel (https://www.amazon.com/gp/product/B000SOIRCG) and used the planes fuel pump to pump back into my tanks, using the filter funnel both going into the tanks and back into the plane. Did get some junk in the funnel, including a dead bug. Probably out of my tanks. However the first five gallons and the last five both took 9.5 minutes for a 31 gph flow rate. Should be plenty.

Doing ground running after flushing the tanks everything ran great. However in my many ground runs I had not been able to replicate the problem. After a long ground run trying to simulate a climb out I could get full power. I decided to fly, and closed the hangar, put on my parachute, etc. Engine then would not start. I suspect vapor lock because of the heat soak from the long run. Oil temp and CHT both read 180. It was getting late, so went home.

This morning got out to the airport to try again. There were some delays on the ground waiting for the tower to talk to me, so the taxi out to the runup area took longer than usual, by the video 10:33 after engine start. This time I was able to replicate the problem on runup. Unable to get full power, stopping right around 2000 rpm. Video link goes to just as I am powering up to full throttle.

https://youtu.be/u0DnhU08hEE?t=80

I taxied back and did some more tests near the hangar. After 30 seconds or so with the fuel pump on I could get full power (2200 rpm) after a brief stumble. With the electric pump off, I can't. See later runups in same video:

https://youtu.be/u0DnhU08hEE?t=231


What do people think? What should I try next? Obviously I don't want to fly again until I can get this fixed.

Setup is O-360A1D with Rotec TBI, Catto 3-blade fixed pitch propeller. Fuel system is per plans, with Van's gascolator on the firewall. Added fuel filter between electric pump and gascolator, is on the cool side of the firewall.

I am leaning toward vapor lock as the cause. Possible fixes - remove gascolator? Have a better filter before it in the system, it currently is only catching water that I missed when sumping the tanks.

Fuel pump shroud and air line to engine fuel pump?

Also, the fuel line running from the pump to the TBI gets close to the exhaust pipe. I put on a heat shield, but that is probably not enough. Move the exhausts down so they go under the nose wheel mount? Re-route that fuel line so it is longer and less direct (maybe 2-3 inches longer), but farther from the exhaust?
 
Only for the sake of possible causes, are your fuel vents open and adequately large enough?
 
What is your fuel pressure in flight? Specifically with the electric pump off and the airplane in a nose up attitude? Does it change with a nose down attitude or the electric pump on?

I'm wondering if you have a problem with the mechanical pump.
 
Vapor lock is not a likely suspect given that you had the problem in the air. Vapor lock usually only occurs on the ground or takeoff roll due to high heat and low cooling flow. I would spend more time confirming that the problem exists only with boost pump off and that it does not occur with the boost pump off. If that is the case, I would suspect the mechanical fuel pump.

Larry
 
I know absolutely nothing about your Rotec TBI, but the 180 degree oil temperatures you mentioned were messing up my MA-3SPA carburetor at idle. I suspected vapor lock at first but that didn't turn out to be the case. It was the heat from the oil sump heat-soaking the carburetor. Good luck.
 
Is the Rotec is a low pressure system (3-6 psi)?

Is that 10 micron filter still in the sytem? If so, where? If it's before the engine driven pump, you may have solved one problem (trash) and created another (vapor lock). Running OK on the boost pump reinforces that theory.

If Rotec says 40 micron, then they've likely determined that 40 is good enough. Sometimes, 'better is the enemy of good enough' (although this is not the correct application of that particular saying).

10 micron filtering, even if the filter is clean, might well be a significant restriction on the low pressure side of the pump. How big is the filter element?

Last, gascolators are near perfect vapor lockers, when placed in the traditional location (low on the firewall, right in the 200 degree exit air, next to the radiant heat from the exhaust pipes).
 
What is your fuel pressure in flight? Specifically with the electric pump off and the airplane in a nose up attitude? Does it change with a nose down attitude or the electric pump on?

I'm wondering if you have a problem with the mechanical pump.

Reviewing videos, fuel pressure in flight is 4-5psi with electric pump off, 6 with electric pump on. Attitude doesn't seem to make a difference, but as this was first and second flight I didn't get very much up or down.

Per the Rotec manual 0.5 to 15 psi should work.
 
Is the Rotec is a low pressure system (3-6 psi)?

Yes, low pressure.

Is that 10 micron filter still in the sytem? If so, where? If it's before the engine driven pump, you may have solved one problem (trash) and created another (vapor lock). Running OK on the boost pump reinforces that theory.

Yes, filter was on system for second flight and today. It is installed between the electric pump and the firewall.

I got this one:

http://www.aircraftspruce.com/pages/ep/fuelfilters/micron10.php

I wanted metal fittings instead of plastic. I calculate the 10 micron part is 1.48 in^2. I couldn't find a 40 micron that was metal instead of plastic. I did get the 31 gph flow even after running 40 gallons through it. That was with the electric fuel pump.

Last, gascolators are near perfect vapor lockers, when placed in the traditional location (low on the firewall, right in the 200 degree exit air, next to the radiant heat from the exhaust pipes).

I put it a bit high on the firewall, but am still worried about that part.
 
Yes, low pressure.



Yes, filter was on system for second flight and today. It is installed between the electric pump and the firewall.

I got this one:

http://www.aircraftspruce.com/pages/ep/fuelfilters/micron10.php

I wanted metal fittings instead of plastic. I calculate the 10 micron part is 1.48 in^2. I couldn't find a 40 micron that was metal instead of plastic. I did get the 31 gph flow even after running 40 gallons through it. That was with the electric fuel pump.



I put it a bit high on the firewall, but am still worried about that part.

Here's the detail that jumps out for me:
"I taxied back and did some more tests near the hangar. After 30 seconds or so with the fuel pump on I could get full power (2200 rpm) after a brief stumble. With the electric pump off, I can't."

If the 10 micron pump is between the boost pump & mech pump, and the fuel between the filter & the mech pump is hot, it sounds like a recipe for vapor lock. The boost pump would pressurize the line, instead of the mech pump sucking on it, which would kill the vapor lock.

Not saying it's for sure the cause, but it should be easy to check; substitute a 40 micron or more filter.

You could also ask Rotec why they only spec'd 40 microns when 10 micron filters are available.

edit: Just re-read the above after posting. Are you saying that the filter area is less than 1.5 square inches?
 
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Fuel Return Line?

Long shot, but does your system have one that runs from the boost pump back to the tank? A friend of mine recently had similar (but different) symptoms after having newly replaced fuel hoses installed during an Annual/Prebuy inspection. We found the Fuel Return Hose was inadvertently swapped with/for the Hose that was supposed to go to the Flow Divider...!
 
This time I was able to replicate the problem on runup. Unable to get full power, stopping right around 2000 rpm. Video link goes to just as I am powering up to full throttle.

The next time it happens, first turn on the boost pump and see if problem resolves. If not, try leaning the mixture to eliminate an overly rich condition. There are 1000's of planes with gascolators and carbs and they don't vapor lock after low speed air work. Is the Rotec new or do you know it's previous history? The rotec han't been sitting for 21 years, has it?

Larry
 
Just a wild shot at this. I know Rotec had a problem with dirt in their Throttle body carbs. They needed to be taken apart and cleaned and that was straight out of the factory. I thought there was talk about it on this forum a while ago but i may be wrong.
 
When you have the loss of power, what are the EGT's doing? In other words, are you rich or lean? Answer that and you can take the next step
 
Thanks for all the help, replying in one post.

Not saying it's for sure the cause, but it should be easy to check; substitute a 40 micron or more filter.

The problem first happened with the gascolator as the only filter.

edit: Just re-read the above after posting. Are you saying that the filter area is less than 1.5 square inches?

Yes, the listing at spruce specified 6 in^2, but taking it apart there are two filters, a bigger screen and then the fine filter. Fine is less than 1.5 in ^2, the screen is a bit bigger. Don't know where they got 6 from.

Something like this would be the 40 micron equivalent:

https://www.summitracing.com/parts/sum-230102/overview/

All the metal ones I can find are about the same filter disc size.


Long shot, but does your system have one that runs from the boost pump back to the tank?

No, no return line.

When you have the loss of power, what are the EGT's doing? In other words, are you rich or lean? Answer that and you can take the next step

The EGTs in flight drop down during the low throttle portion, then slowly come back up as the power comes back on.

In the runup, I find that anything less than full rich runs poorly at full throttle. Anything less than full rich and EGT comes down, RPM comes down and it sounds a bit rough. Sounds like too lean? Every other plane I've flown at these altitudes required some leaning for takeoff.

Perhaps need to open up some holes like in this thread?

http://www.vansairforce.com/community/showthread.php?t=114648

I can take it off and check for stuff inside, but not till next weekend at the earliest. Have to work this weekend.
 
. . .
I can take it off and check for stuff inside, but not till next weekend at the earliest. Have to work this weekend.

While a 10 micron filter is definitely more restrictive, it may not be the core issue. If you had debris contamination, I would definitely dissemble and clean/inspect the TBI. Look with a good magnifier at the small orifices and blow back with compressed air to ensure it is truly clean. I assume the you already cleaned the Rotec "final filter".

Like recommended, I would fit a 40 micron filter with adequate flow area to be sure in the process. I like clean, but the event of stumbling with the boost off is a clear indicator of a suction issue, so either replace it or measure suction at the inlet to the mechanical pump.

Toolbuilder noted the EGT could also provide more direct evidence to leaning, if that is truly the core issue.

Gather as much definitive information you can for a baseline.
 
Thanks for all the help, replying in one post.



The problem first happened with the gascolator as the only filter.

Did you not find trash in the system, the 1st time it happened, before the filter was installed? And didn't the conditions change (now only during heat soaked conditions) after filter installation?

Remember, you can get the same symptom (rough running) from several different causes.
 
Did you not find trash in the system, the 1st time it happened, before the filter was installed? And didn't the conditions change (now only during heat soaked conditions) after filter installation?

Remember, you can get the same symptom (rough running) from several different causes.

I did find trash in the TBI's filter the first time. I also did have what seemed like vapor lock before first flight when swinging the compass, after many short ground runs at the various headings. That was without the filter installed.

Next time I can get to the airport I'll try to get video of a ground run where the EGT gauge can be seen. Works better than taking notes.
 
Did make it out to the airport yesterday, so wanted to give an update. Back to not being able to replicate the problem on the ground. The closest I got was when advancing to full throttle the RPMs go up, then around 2000RPM, go back to 1700-1800 for about half a second and then proceed back up to the 2200 which is all I get with a fixed pitch prop. Aux fuel pump on or off didn't make any difference. Fuel pressure was higher 6-7 psi with the fuel pump on or off.

To check for vapor lock, ran at 1000-1500 for 10 minutes, no change. It was a much cooler day, 60's instead of 80's. After shutting down, taking out the fuel filter to test, and then trying to start back up it wouldn't start, similar to what I suspect was vapor lock before.

Checking EGT, at full throttle and full rich egt is about 1450. Any change from full rich and RPM and EGT both drop. So, too lean?

Checked, I will not be able to move the exhaust down under the nose wheel brace, it hits the cowling if I try that. I will be able to move the fuel regulator back and a bit farther from the exhaust which will also give a shorter hose from the pump.

Took the TBI off to clean it at home, I didn't find large amounts of anything, but six of the holes in the open throttle end of the spray bar were blocked by something. Poked those out with a needle, and then flushed it out with camp stove fuel. Hopefully this makes a difference. I'm saving drilling the holes larger for last as it is something I couldn't undo.
 
...Checking EGT, at full throttle and full rich egt is about 1450. Any change from full rich and RPM and EGT both drop. So, too lean...

The 1450 sounds high but that in itself is not as compelling as the EGT drop with leaning. If you lean at all from full rich and get a drop, then you are right at peak to begin with or are already on the backside of the hill and some distance beyond peak. I'd say this is the first area to investigate. Full rich climb from sea level should give you several hundred degrees rich of peak to play with. Higher altitude runways will even give you more. If you are starting out peaked or even LOP, then thats your stumble/power loss.
 
The 1450 sounds high but that in itself is not as compelling as the EGT drop with leaning. If you lean at all from full rich and get a drop, then you are right at peak to begin with or are already on the backside of the hill and some distance beyond peak. I'd say this is the first area to investigate. Full rich climb from sea level should give you several hundred degrees rich of peak to play with. Higher altitude runways will even give you more. If you are starting out peaked or even LOP, then thats your stumble/power loss.

Thanks, the field is at 4500, so I should have some leaning available. Hopefully the clogged holes will make a difference. I'll try to test this weekend if the hose I ordered gets here in time.
 
First try today after cleaning out the spray bar. For sure a little better. I find I can lean about 1/4" or so at full throttle with a slight rise in RPM, and a also a very slight (25 deg or so) rise in EGT. The EGT change is much slower to respond, have to leave it at the setting for 10-20 seconds to see the change.

Wasn't remotely test flying weather (light rain, cloud bases 6000-7500 MSL, new snow on the mountains around the 7000 level), so deciding not to fly today was easy.

Do you guys think a 25 deg. rise in EGT is enough? Should I go further and drill out bigger holes in the spray bar?
 
It does sound like you are still too lean. At your altitude, it should be WAY rich and take a lot of leaning to get to peak. Instead, it sounds like you are just barely on the rich side of peak now.

So it seems like you have multiple things going on. Hopefully the contamination problem is behind you. That leaves a somewhat excessively lean base mixture setting, and the possibility that there is too much flow restriction upstream of your mechanical pump, although given that you can deliver 31 gal/hr, that sounds good. So it makes your mechanical fuel pump suspect.

Fix the base mixture setting first. You should be at least 200F rich of peak at your altitude. You would like to be something like 150F rich of peak at sea level at take-off power.
 
I don't think it's a fuel flow problem. Yesterday it was the same pump on or off. Fuel pressure is the same pump on or off. The 31 GPH was with the pump on, but having the engine pump running shouldn't make that much a difference.
 
Don't want to be a DenverCoder9, so want to let everybody know what has happened since we last talked about it.

I was hesitant to drill holes in my spray bar (as there's no going back from it), so talked with Rotec on the phone first. They said to send it back and they would rebuild it. Shipping to/from Australia took quite a while, wasn't cheap. Got it back and was on call for a couple of weeks, so couldn't get to the airport. Finally got out this weekend.

Not only was it not running better, it was running worse. Couldn't get near full throttle, engine would die anything over 2000rpm. At 2000, I was clearly running too lean. Tried cranking up the idle mixture, no difference. Decided I need to go back to the beginning and walk thru all the steps. Downloaded the MK.II manual, it is way better than the documentation I got back in 2012.

On page 39 for full rich adjustment it has you run it with all inlet ducting removed, and only a 1/16" mesh screen. Tried that this morning. Ran with no problems. At full throttle get about 2250 RPM, can run 175 degrees (F) rich of peak. Clearly the problem is my inlet ducting. The running worse is probably due to temps in the 50's and 40's and so denser air.

So, looks like I need some kind of flow straightening. Easy enough to pick up some honeycomb aluminum, but I have a question: Is it better to have the grid as close as possible to the intake, or should I have it down by the top of the FAB with a round duct going to the intake?

Currently I have a 4 inch long square duct, was easier to make, but I believe it is the cause of the problem.
 
Photos?

Solving mixture problems is a black art, but look at the good side: You've given your fuel system a good cleaning and that's one less thing to worry about. I'm not sure the problem is your airbox geometry. The airbox recommended for my Lancair was a thin rectangular shape with a hole in the top for the carburetor - no turning vanes or anything. I didn't use that design but apparently it worked. But that was a carb with a circular venturi, not a throttle body with a spray bar. Do you have an air filter in the intake? It would help if you could post photos of your airbox setup.
 
Do you have any amount of ram air pressure in the intake? Per the conversations I've had with Rotec this will cause an extremely lean condition as the TBI requires a considerable vacuum to draw the fule through the spray bar.
 
Do you have any amount of ram air pressure in the intake? Per the conversations I've had with Rotec this will cause an extremely lean condition as the TBI requires a considerable vacuum to draw the fule through the spray bar.

How could I tell? I don't have any pressure gauges in the area. I would expect I have some, it is the standard forward facing intake.
 
The option #2 you show in previous post looks like it could generate some ram pressure can you remove the bottom of the air filter housing that creates the duct and replace with a cover plate to only seal the air filter ,to test performance with only static air available.
 
Years ago Van went through a lot of different ideas to resolve problems very similar to yours on his RV-4 equipped with an Ellison throttle body (which I believe is very similar to what you are using).

The Ellison is very sensitive to inlet flow. It seems to be particularly troublesome on installations where there has to be an abrupt change in direction of the induction flow just before entering the throttle body. Many different flow straightening devices have been used by users of the Ellison.
I think the engine currently has a vane style (basically two metal plates intersecting as a cross) flow straightener installed for the past 20 years or so, but even with that I think it is still a bit short of ideal performance (I have never flown the airplane but I have worked on the engine many years ago).
 
TBI

Block off snout and remove intake channel go fly see if any difference,if still a problem can anybody say carburetor.
Bob
 
Years ago Van went through a lot of different ideas to resolve problems very similar to yours on his RV-4 equipped with an Ellison throttle body (which I believe is very similar to what you are using).

The Ellison is very sensitive to inlet flow. It seems to be particularly troublesome on installations where there has to be an abrupt change in direction of the induction flow just before entering the throttle body. Many different flow straightening devices have been used by users of the Ellison.
I think the engine currently has a vane style (basically two metal plates intersecting as a cross) flow straightener installed for the past 20 years or so, but even with that I think it is still a bit short of ideal performance (I have never flown the airplane but I have worked on the engine many years ago).

I flew a Starduster with an Ellison for many years, was finicky on mixture setting, but had Ok performance (for a draggy open cockpit biplane). That gave me the encouragement to try the Rotec. Still hoping for affordable inverted capability.

If it doesn't work out, I do have the carb that came with the engine. Of course, its been sitting on a shelf for 15 or so years as well.
 
Years ago Van went through a lot of different ideas to resolve problems very similar to yours on his RV-4 equipped with an Ellison throttle body (which I believe is very similar to what you are using).

The Ellison is very sensitive to inlet flow. It seems to be particularly troublesome on installations where there has to be an abrupt change in direction of the induction flow just before entering the throttle body. Many different flow straightening devices have been used by users of the Ellison.
I think the engine currently has a vane style (basically two metal plates intersecting as a cross) flow straightener installed for the past 20 years or so, but even with that I think it is still a bit short of ideal performance (I have never flown the airplane but I have worked on the engine many years ago).

I have been around this for awhile and my recollection was that Van developed the FAB because of the Ellison TBI. As I recall it likes a dirty airflow and this was a solution to accomplish that. I had a standard FAB mounted directly to an Ellison TBI on my 0320 powered RV4 for the entire time I owned the airplane with no issues.
I wonder if you used option 2 if that isn't creating the problem of the airflow straightening its self out again prior to entering the Rotec.
Just something to consider. These are very sensitive to airflow.
Ryan
 
Do you have a Mk I or Mk II Rotec TBI? The Mk I's have a separate pressure regulator.

I had a Mk I 40-4/5 and suffered vapour lock several times last (Australian & flamin' hot) summer, replaced it with a Mk II 48/4-5 and now run Avgas on the ground and it 'seems' to have fixed it - but I am going to remove the Vans gascolator too when I get around to it.

One thing I did observe with my symptoms was the fuel pressure did not fluctuate as you would expect, nor did the electric fuel pump solve things or change the pressure. One thing I did come across was a suggestion to blast-cool the regulator would go a long way to helping things, though that went in the too-hard-basket for me at the time.
 
Do you have a Mk I or Mk II Rotec TBI? The Mk I's have a separate pressure regulator.

Have the Mk I. Have had vapor lock (I think) on the ground after shutting down with long ground runs. Once of the things they did to it after I sent it back to the factory is set it up for a return line to help with vapor lock. Also have the parts to set up a air blast.

Designing all that will come after I get it working. Don't want to drill holes for air blast and return lines if I end up going to the carb.
 
Rotec TBI

I have a Rotec MK1 on my O-360 powered 7. Cold starts are good using the primer for a couple seconds while cranking. I installed it as you did in pic 2. I made the adaptor between the carb and FAB 6" in diameter to act as a plenum. I also installed a 1/4" thick phenolic spacer between the TBI and sump to reduce heat transfer. I have a blast tube on the regulator which is mounted as per the instructions close to the inlet and parallel. Fuel lines all have fire sleeve. I used the same filter as you from Spruce installed just after the gascolator. I also installed 40 micron Summit filters at the outlet of each tank and use a Steve's gascolator in the Vans location. Started flying it in July this year and have about 90 hrs on it so far. So far so good! Rocket Bob has done a lot of testing on Rotec's on his O360 with good success. Check out his posts...in the RV4 section I think. Rotec now recommends a fuel return line to eliminate the vapour lock issue. I have not installed one yet and my only issue is hot starts...have to start it like it was injected....seems to flood when stopped hot. It idles down to 400 rpm and could even be set lower. WOT at 8000' DA and it will run up to 2800 rpm on the Sensenich 85" pitch RV prop.
Good luck!
Al
Edit: I also installed a V shaped piece of .032 about 4" long in front of the filter element to force the air around the outside of the filter and to mitigate the ram effect which the TBI does not like.
 
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Got a flow straightener built. Need to get better bolts, anybody know where I can get 3.75" long drilled head bolts with 1/4" coarse thread? (I guess I could use grade 8 with lock washers).

img_4400.jpg


Hopefully will be able to get out to the airport next weekend.
 
Well, that didn't help at all. I'll try doing the round duct first with the honeycomb right next to the TBI for my next try.

Also had a thought after I got home from the airport, could be leaking around the alternate air door, that would make fore very swirly air. Can just tape over that for a test.
 
That extremely sharp edge on the inlet to your "flow straightener" is probably doing more harm than good too.
 
You should consider calling Don Rivera at Airflow performance. He makes a really nice airflow straightener for the injection systems he will probably sell you.

Vic
 
That extremely sharp edge on the inlet to your "flow straightener" is probably doing more harm than good too.

I had the same thought, but making a nice round one wouldn't be easy. Would either need to use fiberglass or learn metal spinning. Will try the easy stuff first.
 
TBI advice

You may find useful information at ( forum.rotecaerosport.com ) Quite often Paul answers questions directly as "Administrator "
 
Flow straightener Mk.II:
img_4553.jpg


Got it installed and did some test runs today. Much better. Can get the 80deg drop from full rich at full throttle (just barely). The EGT response is much slower than RPM, so it takes a while to test. Still has the sharp corner right at the entrance, but the grid right up against the TBI.

Taping over the alt air door didn't make a difference, so leaving that as it is.

Wasn't remotely flying weather (mixed snow and rain), but Monday afternoon looks possible. I may just have a flying airplane for Christmas.
 
What with work obligations and winter weather, didn't get to fly until yesterday. (somehow the weather was great every weekend I was on call) Worked great. No problems with idle to full throttle. Can now start opening up the envelope.

Was truly a beautiful day to fly.

Jan27.2.jpg



Thanks for all your help, I just don't know enough about engines.

May still try to build the rounded duct entrance, but not a rush.
 
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