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Fuel Pressure Issue EFII

dmattmul

Well Known Member
I now how 35 hours in my RV14A with the IO-390. First 32 hours were perfect and the EFII system (Fuel Injection and EI) has been great, very very smooth. Starting a few hours ago instead of seeing a slight decrease in fuel pressure (28.7 in. mp and 42 psi) at I take off and slight decline when in cruise (22.0 in. mp and 39 psi) and now seeing at take-off 29 psi and 34 psi in cruise. Idle still around 40 psi. I have not contacted EFII yet and will try tomorrow. (Robert has been extremely helpful this last 3 years during the build and engine run-up) Checked the fuel flow and it's ~ 50 GPM ok. (35 GPM min.). Seems the filters must be ok. (It has a pre-pump filter and a post pump filter) The regulator is plumbed per instructions and the mp line to the regulator appears to be fine. Any suggestions?
 
Pressure

Did Robert tell you to set 42 psi?

I set mine up per the instructions at 35 psi static which is about 28 psi while running. I actually called him to verify 35 psi static and not while running....
 
35 psi is correct

35 psi is the correct set point. It worked quite well at 42 psi so right or wrong left it there. I’ll don’t think that is the issue but will ask Robert. Issue might be self inflicted but won’t be the last.
 
Just a data point, but my SDS system is set to 49 and does not move more than a few PSI regardless of fuel type (100 LL or regular unleaded), OAT or power setting. SDS fuel module, Borla regulator. Bulletproof.
 
Just a data point, but my SDS system is set to 49 and does not move more than a few PSI regardless of fuel type (100 LL or regular unleaded), OAT or power setting. SDS fuel module, Borla regulator. Bulletproof.

Just a data point, but my EFII system is set to 35 and does not move more than a few PSI regardless of fuel type (100 LL or regular unleaded), OAT or power setting. Bulletproof. USA company!
 
Maybe disconnect & plug the MAP line at the regulator. Take it for a test flight & see if it holds constant pressure. This might shed some light on the MAP input.
 
fuel pressure

We set the static fuel pressure to 35psi (engine off, one pump running).
If you ever had a leak in the fuel rail, this minimizes the volume of fuel leaked.
Fuel pressure is manifold pressure referenced. I.E. it goes up and down with manifold pressure. This function is driven by the manifold pressure line that is connected to the fuel pressure regulator.
The normal operating fuel pressure is 35psi at high manifold pressure to approx. 25 psi at the lowest manifold pressure.
This function can easily be tested without running the engine if there is a question of how it is operating. You can get a $20 Mighty Vac hand vacuum pump at the auto parts store (breaker bleeder kit). Attach the hand vacuum pump to the pressure port of the regulator. Now you can simulate all manifold pressures and run the regulator through it's full operating range.

Fuel pressure sender anomalies are common. If there is any question about your fuel pressure reading, it is always a good check to test the fuel rail pressure with a mechanical gauge and make sure your engine monitor agrees with the mechanical gauge.

Fuel pressure senders can be affected by vibration, sensor grounding (on one wire senders), and wiring.

Robert
EFII
 
Pressure change

OK, seems I need to do a little more work and check my install. This could be anything from FP sender error to avionics interference to who knows what. That is what we experimental builders do to troubleshoot our airframes and make us better builders. Let's all learn from my experience/errors.
 
Sender error

The flow GPM checked ok (38 GPH) I so it wasn’t the filters or possibly a check valve issue. The culprit is the sender. Mechanical gauge installed fuel pressure goes up slightly as suppose to with higher manifold pressure. The sender is mounted to the fire wall through the tri-manifold setup Vans uses on the 14. I’ll see if I can better isolate this in case vibration is the issue. If not need to learn to live with 32 psi indicated on departures.
 
Dwight----IF the sender is grounded by the body, an over abundance of thread sealer 'might' be giving an intermittent ground. Just a theory---had it happen once years ago in a different application.
Tom
 
Answer

Noticed I never did post the resolution or at least not on this thread. The issue was self-inflicted and want to thank Robert, Steve and all the great RV suppliers out there for the help. Turns out that I had a very slight leak on the input side of the pump in the tunnel. It never leaked fuel, (When I was in the airframe), did not smell because the system is not at any pressure on this side of the pump. (There was a very slight blue stain under the fitting) This small leak must have occurred after each shutdown when I was not in the airframe. The leak allowed air bubbles to enter the system and vibrated the fuel pressure regulator seat damaging it. Last 100 hours system has worked great. Last conditional looked over the tunnel very closely. (Should have installed access panels to make this inspection easier but with pre and post fuel filters located there probably disassembly is the better alternative.
 
Noticed I never did post the resolution or at least not on this thread. The issue was self-inflicted and want to thank Robert, Steve and all the great RV suppliers out there for the help. Turns out that I had a very slight leak on the input side of the pump in the tunnel. It never leaked fuel, (When I was in the airframe), did not smell because the system is not at any pressure on this side of the pump. (There was a very slight blue stain under the fitting) This small leak must have occurred after each shutdown when I was not in the airframe. The leak allowed air bubbles to enter the system and vibrated the fuel pressure regulator seat damaging it. Last 100 hours system has worked great. Last conditional looked over the tunnel very closely. (Should have installed access panels to make this inspection easier but with pre and post fuel filters located there probably disassembly is the better alternative.

I had a similar issue on my SDS, I had changed out all my rubber components on the fuel system for running 93E10, but I missed ONE seal on a fuel prefilter, upstream of the pumps, on the left tank. The O-ring deteriorated from the E10 fuel, cracked, and started sucking air. Hard to find... I ended up draining the tanks and pressurizing with air, and spraying soap water all over every fitting before finding it.

It's the little things....
 
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