Fuel Pressure

Doug Rohrer · #1 05-13-2010, 04:16 PM

I bought a flying RV-9A about a year ago, and have flown it 80 fun-filled hours since then. It has a Lycoming O-320 engine. During this time, I have seen the fuel pressure on the Van's gage creep up to around 10 psi when running on the mechanical fuel pump. The gage has a red mark at 8 psi. The electric boost pump goes up to 8 psi with the engine off. These pressures all seem too high, but I don't know what the prefered range is. What is the desire range, and how is the pressure adjusted? Thanks.

Doug

David-aviator · #2 05-13-2010, 06:31 PM

Quote:

Originally Posted by Doug Rohrer

I bought a flying RV-9A about a year ago, and have flown it 80 fun-filled hours since then. It has a Lycoming O-320 engine. During this time, I have seen the fuel pressure on the Van's gage creep up to around 10 psi when running on the mechanical fuel pump. The gage has a red mark at 8 psi. The electric boost pump goes up to 8 psi with the engine off. These pressures all seem too high, but I don't know what the prefered range is. What is the desire range, and how is the pressure adjusted? Thanks.

Doug

The indicating system may be what's creeping up, not the pressure.

L.Adamson · #3 05-13-2010, 06:40 PM

Quote:

Originally Posted by David-aviator

The indicating system may be what's creeping up, not the pressure.

Could be, as mine did. However, I did short out a few of Van's gauges when I had my center gauge panel out for radio work, and accidently shorted it out with the panel frame. The fuel pressure seemed to work after that, but started creeping up past the red line, especially when pushing the throttle in. Since they are cheap, I replaced both the sender and gauge. No problem since.

L.Adamson --- RV6A

Doug Rohrer · #4 05-13-2010, 07:39 PM

I can plumb in a temporary gage and run the electric pump to compare readings. What should the pressure be?

Doug

IowaRV9Dreamer · #5 05-13-2010, 08:32 PM

My lycoming manual says 0.5-5.0 psi.

Doug Rohrer · #6 05-14-2010, 12:42 PM

Thanks for the pressure range. I will check it tomorrow. After reading about all the grief involved with changing fuel pumps, I sure hope it is the transducer. Apparently there is no adjustment for fuel pressure...

Doug

DEWATSON · #7 05-14-2010, 01:09 PM

I absolutely do not know what I'm talking about, but I don't think the spring in a mechanical pump can strengthen with age. It seems logical that the pump would decrease it's pressure as time passed and the spring weakened. Even if the outlet was completely blocked, I don't think the pressure would increase past the spring's strength. BUT, what do I know? I think I would take a look at the gauge first. Good luck.

Kent Ashton · #8 05-14-2010, 03:48 PM

I had weird fuel pressure indications for a long time until I went to a shielded wire for the signal wire from the sender to the gauge (on a Cozy IV). If you have an electric sender, that might be worth a try. Ground the shield on the neg. post on the gauge and leave the other end of the shield open.
-Kent

DennisRhodes · #9 05-14-2010, 06:56 PM

I also had high fuel pressure indication problems with a carb'd 0320. As well as low pressure indication at times. As it turned out the fuel pressure transducer was defective. The transducer came with the Dynon 180 installed new. Seems that the tranducers are many times the problem . You might be sure that the ground wire at the transducer is attached securely to a GOOD ground as this will also cause false readings. Check Summitt Racing catalog for a replacement transducer. 0-10 PSI range for carb set up.

Doug Rohrer · #10 05-15-2010, 05:24 PM

For all you guys breathlessly awaiting my findings, I am glad to report a real mechanical pressure gage I temporarily hooked up showed a max of 4.5 psi during a runup on the ground. The electric boost pump got it up to 5.5 psi. So the problem is either the transducer or the gage; I am betting it is the transducer. A new one is on order. Thanks to all for the help.