Fuel Pressure

paul330 · #1 07-30-2016, 10:41 AM

I have just moved my aircraft to South Africa where it has under gone a full inspection/annual. I have just been closing everything up and doing the engine run.

Before I left UK, I had an issue on the last couple of flights where the fuel pressure would fluctuate and get low (around 15 psi) on the ground but was fine in the air. Putting the fuel pump on resolved the problem. On stripping down to move, I noticed that the bottom plate on the fuel pump was loose with 4 of the 6 screws unthreaded. I thought maybe this was the problem.

Before draining the oil, I did a run. Initially, it was a bit rough and the fuel flow was low. After a couple of minutes, it sorted itself out. Running was smooth and fuel pressure normal at around 26. I put the symptoms down to inhibitor oil in the cylinders and air in the fuel system and thought that the problem had been solved. After the oil change, I did a further run-up. Terrible! Firstly, fuel pressure was good and everything smooth. Then it went high - 37 - but the engine ran fine. No matter what RPM I set, it stayed constantly high. Then it dropped and I had the same symptoms as previously - fuel pressure low, engine stumbling but would pick up with more throttle but at times it was really rough. Putting the electric pump on would increase the pressure but it still wasn't 100% smooth.

This was a Aerosport IO540 which had been running SOOOO sweetly so you can see why I am totally hacked off! I am not very switched on with pistons being military all-jet trained but I suspect the issues could be fuel pump, pressure regulator or induction/injection. Any thoughts would be welcome.

EDIT: I have checked the serial number on the pump and it is not subject to any of the SBs.

climberrn · #2 07-30-2016, 06:07 PM

I had a recent intermittent issue with a mechanical fuel pump on my injected Lycoming. Same symptoms as yours, with the exception of the high pressure. Talked to several people and thought it was the sending unit. Pressure dropped in flight and engine coughed. New mechanical FP installed and FP ruins rock solid at 29 psi. Was 24-25 before.

After the new one was installed I did an autopsy of the old pump. It appeared OK, but there are 2 one way valves, and I bet 1 was malfunctioning. The best $375 I have spent in a long time...

Airflow performance was very helpful, and gave me suggestions to try. As soon as it coughed in flight, with a FP drop, that was enough to get my attention.

paul330 · #3 07-30-2016, 11:30 PM

I was thinking that way but rather hoping there could be a quicker fix. The engine only has 35 hours running but I seem to remember reading that many fuel pumps have developed faults at around that time

Think I might get in touch with Aerosport and get their thoughts......

paul330 · #4 08-04-2016, 10:32 AM

Found the problem - not only that, but I believe I have also solved this issue:

http://www.vansairforce.com/communit...d.php?t=132255

Two birds with one stone - love it......

There was a leak at the fuel selector from the left tank - hence the previous intermittent fuel leak. The engine had been sucking air and it was really bad on the last run because I had put very little fuel in the tanks and the leak was at the high point in the fuel system. It ran smoothly on the first run because I was on the right tank.

I found the leak by pressurizing the fuel tanks through the vent to about 4psi.

She is now running back to her sweet, smooooth self.