Frustrated with low fuel fuel pressure readings. Carbureted 0360

[stringbender]

My experience has taken 2 years approximately 180 flight hours.
equipment is GRT EIS 4000 indicating system.
Carbureted 0360
direct pressure gauge reading on ground = 5psi engine driven pump and 6psi with engine running and electric pump on.

problem; minimum fuel pressure exceeded. Although this has been rarely occurring I have changed the pressure transducer 3 times attempting to fix.
I have inspected the ground is good.
resistor = correct value (200 ohms).

I have decided to install a direct press gauge in the cockpit. Unless I figure a good way to secure The transducer and prevent multiple fuel fitting connections I will not include it. I can’t find the right manifold.

I plan on using AN4 stainless steel beaded hose (phenix).

I would prefer to keep the transducer.
any suggestions?

regards
Doug

 

[BH1166]

What do you have AUXsf and Auxoff set to on eis4000? You said you are grounded, where? I learned best to use same ground the Eis4000 is using (pin 1), not what is convenient to use ( close by).

 

[lr172]

How would you know that you exceeded the minimum? Lyc says min pressure is .5 PSI and most gauges won't read that low.

Larry

 

[Sam Buchanan]

Are you familiar with the well-documented characteristic of fuel pressure senders on carbed engines that frequently cause low pressure indication? The fact you have changed the sender multiple times leads me to think you are seeing what is fairly common with carbed RVs. The sender is vented to atmosphere and sometimes, especially during a climb, will show low pressure until the pressure in the sender equalizes with ambient pressure.

Many, many threads about this issue in the VAF archives.

 

[stringbender]

What do you have AUXsf and Auxoff set to on eis4000? You said you are grounded, where? I learned best to use same ground the Eis4000 is using (pin 1), not what is convenient to use ( close by).

I have made many adjustments to scale factor and offset....I started out using what GRT advised however it was not accurate on the low end....at present the readings in fuel pressure is .1 without the engine running.....so I set the alarm to .7psi
I forget what the SF/OFF is currently, the highest it goes is 8 psi which is a couple higher than actual.
I used a multi meter to measure resistance to ground. Possibly I should try to use pin 1?
Doug

 

[stringbender]

Are you familiar with the well-documented characteristic of fuel pressure senders on carbed engines that frequently cause low pressure indication? The fact you have changed the sender multiple times leads me to think you are seeing what is fairly common with carbed RVs. The sender is vented to atmosphere and sometimes, especially during a climb, will show low pressure until the pressure in the sender equalizes with ambient pressure.

Many, many threads about this issue in the VAF archives.

Yes I have.
Should I maintain it a nuisance and live with it......at this point I am more interested in operating the plane at least for 25 hrs and see what the mechanical fuel pressure guage will indicate in flight.
I'd hook up both if I could do so with a better manifold/bulkhead. I don't what to have too many fuel connections/multiple hoses.

 

[stringbender]

How would you know that you exceeded the minimum? Lyc says min pressure is .5 PSI and most gauges won't read that low.

Larry

When the guage touch'es the half psi bar or lower.
Good question.
This is going to be interesting to see the trend of the engine driven pump through different phases of flight, usually the light would be on assent after take off 800' to 2000'.

 

[BH1166]

I have made many adjustments to scale factor and offset....I started out using what GRT advised however it was not accurate on the low end....at present the readings in fuel pressure is .1 without the engine running.....so I set the alarm to .7psi
I forget what the SF/OFF is currently, the highest it goes is 8 psi which is a couple higher than actual.
I used a multi meter to measure resistance to ground. Possibly I should try to use pin 1?
Doug

The “to pin one” has worked for me. Oil temp 10f off , change ground, now matches cht egt 2 days after shutdown. No guarantees Doug, but worth the effort, and I hope it works for you.

 

[stringbender]

My experience has taken 2 years approximately 180 flight hours.
equipment is GRT EIS 4000 indicating system.
Carbureted 0360
direct pressure gauge reading on ground = 5psi engine driven pump and 6psi with engine running and electric pump on.

problem; minimum fuel pressure exceeded. Although this has been rarely occurring I have changed the pressure transducer 3 times attempting to fix.
I have inspected the ground is good.
resistor = correct value (200 ohms).

I have decided to install a direct press gauge in the cockpit. Unless I figure a good way to secure The transducer and prevent multiple fuel fitting connections I will not include it. I can’t find the right manifold.

I plan on using AN4 stainless steel beaded hose (phenix).

I would prefer to keep the transducer.
any suggestions?

regards
Doug

A friend told me recently, the drop in pressure associated with carburetor float movement.

question?
Is there anyone with the similar GRT EIS Transducer AND direct pressure line/gauge installed?

if so could you send me pics of your install please.

THANK YOU Vans aviators and builders for your consideration/views/remarks.
Doug

 

[BH1166]

I chased fuel pressure like you. I used pressure gauge only to verify pressure, then figured out how to get it to read correctly via EIS4000. My install had wrong resistor, I fixed that issue and all is good. I swore my previous attempts were due to bad sender, I have 3 off them in a bag lol. I use a VDO 360 043 and all is good several years now.

 

[stringbender]

I chased fuel pressure like you. I used pressure gauge only to verify pressure, then figured out how to get it to read correctly via EIS4000. My install had wrong resistor, I fixed that issue and all is good. I swore my previous attempts were due to bad sender, I have 3 off them in a bag lol. I use a VDO 360 043 and all is good several years now.

Thanks, I have a spare also and let’s not forget about the ones I replaced, there probably still good.

I was hoping the resistor value was the wrong value installed but it’s correct.

I just need to fly around for 25 hrs With my direct pressure gauge.

 

[penguin]

With respect you are over thinking the problem, my view is similar to Sam's. Fuel flow is important, pressure is not. Flow fills up the float bowl rather than pressure. If the engine does not stop then flow is adequate and the low pressure warning is not accurate. Put the minimum pressure down to zero and carry on knowing tah the indicated pressure will always be low during a climb.

 

[Frank Smidler]

I had the same issue for years. With the electric fuel pump on, no issues. With only the mechanical fuel pump, pressure was OK in level flight but would go low if I started to climb. I just lived with it by turning on the electric pump when I went into a climb. Eventually I decided to change the mechanical fuel pump and in the process found the true cause of low pressure, the o-ring on the intake side of the mechanical fuel pump had a slit in it that would cause air to be sucked in with only the mechanical pump. Replaced the o-ring and problem solved.

 

[stringbender]

I had the same issue for years. With the electric fuel pump on, no issues. With only the mechanical fuel pump, pressure was OK in level flight but would go low if I started to climb. I just lived with it by turning on the electric pump when I went into a climb. Eventually I decided to change the mechanical fuel pump and in the process found the true cause of low pressure, the o-ring on the intake side of the mechanical fuel pump had a slit in it that would cause air to be sucked in with only the mechanical pump. Replaced the o-ring and problem solved.

Frank
i changed my o ring on my outlet fitting.

probably didn’t check the inlet, however changed the lines (tight lines).

l will post pics of my minor alteration.
Doug

 

[stringbender]

Here is my install of my minor alteration.
I needed a 12vdc supply for my iPad where I receive my ADSB in and ForeFlight information.

items used: gauge is non liquid filled., phoenix stainless braided line and fittings, AN4 bulkhead fitting / on firewall.

results: start up = 6 to 7 psi.

cruise at 5,500’ = 3 to 3.5 psi.

im not sure if altitude has a way of reducing the gauge readings?

Anyone have more experienc in this?
Doug

 

[don.olandese]

I had the same issue for years. With the electric fuel pump on, no issues. With only the mechanical fuel pump, pressure was OK in level flight but would go low if I started to climb. I just lived with it by turning on the electric pump when I went into a climb. Eventually I decided to change the mechanical fuel pump and in the process found the true cause of low pressure, the o-ring on the intake side of the mechanical fuel pump had a slit in it that would cause air to be sucked in with only the mechanical pump. Replaced the o-ring and problem solved.

 

[newt]

Doug, it's hard to see what you're trying to fix here.

It's common -- to the point of being normal -- for the automotive (VDO) fuel pressure senders commonly used on carburetted RVs to read low during climb. Cars never climb at 1000fpm, so being accurate under those conditions is not part of the design brief. They're not air pressure compensated, and behave pretty much the way you've described.

Unless your engine is stumbling, you don't have a real problem.

Before I switched my O-320 into an IO-320, I used to get fuel pressure drops during steep climbs. It'd "recover" if I turned on the electric pump, but nothing bad ever happened if I left it turned off and ignored the gauge, so that's what I did. If I ever lost engine power and the gauge was 0 then I'd know it was a fuel supply problem, but as long as the engine was running fine the gauge reading didn't really matter so I didn't pay attention to it.

With a fuel injection conversion and a G3X Touch system, all the sensors got replaced, and now the Kavilco pressure transducer on the fuel line reads constant regardless of attitude or climb rate.

It seems to me that your alternatives are to either buy a pressure transducer that's a better match for aircraft applications, or set your minimum alert threshold to zero and live an alarm-free life. I don't think you're going to get a lot of satisfaction by chasing wiring and replacing sensors. Unless I'm missing something, what you've described is nominal for the equipment you have.

- mark

 

[stringbender]

Ok lots of that’s just the way it is.


Aircraft limitation exceeded.
I did something to see what the trend is.
I have not said “it only happened on climbout”.

I am going to fly it for 25 hrs and monitor my trend.
I have a GRT EIS 4000 which would bounce around digitally. It’s not a EFIS, a tape,or a round dial.

I have concerns of a failing fuel pump. That is why I installed a direct pressure fuel gauge, I could have added another fuel line and hooked up the VDO transducer (which is not an AIRWORTHY part per manufacturer; not for use in fuel systems, not for use in aircraft, but did not want to add additional fuel connections.

 

[Sam Buchanan]

I have concerns of a failing fuel pump. That is why I installed a direct pressure fuel gauge, I could have added another fuel line and hooked up the VDO transducer (which is not an AIRWORTHY part per manufacturer; not for use in fuel systems, not for use in aircraft, but did not want to add additional fuel connections.

I have experienced a failing fuel pump on my carbed O-320 and it was definitely a different scenario than the erratic pressure readings we often see. The bad pump would result in a random loss of rpm during a climb which would be instantly resolved by turning on the boost pump. I had been noticing lower pressure than usual for awhile but no running issues until the pump was seriously ill. After experiencing this a couple of times I replaced the pump and all was good with better pressure even though variations could still occur.

I have been using VDO sensors since my RV-6 was built in 1999. My original uMonitor came with the senders and the JPI monitor I installed last year also uses VDO sensors.

 

[Paul 5r4]

From day one my Dynon system has read a pressure that to me seems a little low, especially at altitude and cruise settings. Of course I checked everything and all is good. It bugged, (worried, even scared), me to the point that I eventually put in an old style mechanical fuel pressure gauge. Never once has it read too low. In cruise, the Dynon will be reading 1/2 lb and the old style reads no lower than about 2 lb. KNOWING that the fuel was under enough pressure to get to the fan was important so it was worth it to me. Even at max pressure the Dynon reads lower than the other.

 

[stringbender]

I have experienced a failing fuel pump on my carbed O-320 and it was definitely a different scenario than the erratic pressure readings we often see. The bad pump would result in a random loss of rpm during a climb which would be instantly resolved by turning on the boost pump. I had been noticing lower pressure than usual for awhile but no running issues until the pump was seriously ill. After experiencing this a couple of times I replaced the pump and all was good with better pressure even though variations could still occur.

I have been using VDO sensors since my RV-6 was built in 1999. My original uMonitor came with the senders and the JPI monitor I installed last year also uses VDO sensors.

Sam
Thanks for your info on what you experienced on a failing pump.
I would like a JPI monitor....and I understand VDO senders are in LOTS of applications fuel/aircraft. Probably a liability issue.
I was told by a EAA mentor that fuel pumps basically have a 20 yr life....
I do not think the part has a TBO limit.
I have a call into Product support with Lycoming.
They remarked 8psi max
3 psi desired
.5 minimum
for the 0360-A1A
They are researching more on "why the fuel pressure drops".
So far my direct pressure guage experience (3 flights) I do not SEE THIS trend.
regards
Doug

 

[stringbender]

From day one my Dynon system has read a pressure that to me seems a little low, especially at altitude and cruise settings. Of course I checked everything and all is good. It bugged, (worried, even scared), me to the point that I eventually put in an old style mechanical fuel pressure gauge. Never once has it read too low. In cruise, the Dynon will be reading 1/2 lb and the old style reads no lower than about 2 lb. KNOWING that the fuel was under enough pressure to get to the fan was important so it was worth it to me. Even at max pressure the Dynon reads lower than the other.

Paul
I am glad to have company in this similar situation.
I have 3 flights on my install and it is behaving like yours in that it does not drop below just under 3 psi (2.7 approx) in flight.

Regards
Doug