Fuel pressure varies with rpm?

Is it normal for fuel pressure to fluctuate with engine demand? Fixed pitch prop, measured downstream of the TB, spec is 2-6 psi. I measure 5.6 psi at 1000rpm, 3.8 psi at 1400rpm, and 2.3 psi at 2150rpm. This is engine driven fuel pump only. I'm going to be checking into possible restrictions or blockage I. The fuel system, as this seems excessive to me. The pa28 I usually rent hangs about 3psi all the time. What do you see normally?

seems like you are using it faster than you can deliver it. Some sort of fuel delivery restriction or problem would be my guess.
Good Luck,
Mahlon

Or an air leak

Check the fittings in the lines for an air leak. Ensure they are all torqued properly and no cracked flares.

Vic

How often does an engine driven fuel pump go bad?

Just sitting level, i tested for fuel flow on the electric pump. I get ~36gph left and 24gph right. I'll be looking for the disparity, and this is just free flowing, but this would suggest the flow path is ok I think. The previous numbers were enge pump only. I will test both ways tomorrow, assuming I've nailed the rough running issue. When the pump is seeing air it gets loud.

Long subject

This could stretch into a long string of what if's. Fuel supply on the up stream side of the engine driven pump can be effected by a number of things. Line size, inlet blockage, sharp bens in the lines, fittings being drilled to small in the "I.D.". You name it. The best think to do is start at the pick-up and go down stream all the way step by step and check it all to be open and flowing as much as needed. The book by F.S.D.O. I think says 150% of what it the engine will need when it is at 100% power. I like to see a little more, but that's just me. It is not all that unusual to see some drop in pressure after the engine driven diaphragm pump in a fuel system of a low-wing aircraft. That is why we see a small transfer pump between the tank and the engine driven pump. That's the one you turn on at take-off and landing to be sure you get fuel to the engine driven pump out of a low wing aircraft, were the delivery pressure to the engine is most often negative and the engine driven pump must suck it up to it's location in the system. You get the idea, that is why I like wide open good sized lines with a little more than the 150% asked for. Fuel starvation is one of the top reasons for forced landing in low wing aircraft and high-wing. Just a thought here, Yours as always, R.E.A. III #80888

Thanks...

I have yet to do the angle of attack 150% test. I think the issue I was chasing, rough running, climbing EGTs, high fuel pressure variation were related to the same thing....a partial obstruction not allowing the injection daiphragm in the injector to close. This caused significantly higher than normal fuel consumption - at idle throttle it was a constant small stream of fuel! It fed well from both tanks today on the ground. I'd still like to pin down the why, but maybe after the aoa test. Thanks all, some gtreat thoughts here.