AFP fuel pump - excessive pressure?

RV10Rob · #1 02-12-2011, 02:32 PM

Hi, all... when turning on my AFP electric fuel pump with the engine off, I'm seeing pressure stabilize at 78 psi, which I know is high. After I first turn it on, it builds pressure for a couple seconds, then I hear a "pop" when it stabilizes at 78. Could this be something wrong with the bypass valve?

BTW, during my engine ground run, with the electric pump off, I was seeing 27-28 psi, so don't think it's the transducer.

Thanks..,

-Rob

Mike S · #2 02-12-2011, 03:59 PM

Quote:

Originally Posted by RV10Rob

Could this be something wrong with the bypass valve?

\

Sure sounds like it, but call AFP Monday would be best, IMHO.

Quote:

Originally Posted by RV10Rob

BTW, during my engine ground run, with the electric pump off, I was seeing 27-28 psi, so don't think it's the transducer.

Thanks..,

-Rob

Thanks for adding this bit of info-----I was going to say you had a sender problem, but I guess not.

frankh · #3 02-12-2011, 06:40 PM

The AFP system is OK up to 90psi.

I would like my pressure to be a bit lower though.

Sounds like the bypass valve is either stick or the spring is too strong.

Frank

Don at Airflow · #4 02-13-2011, 10:20 AM

Sounds like the pressure is dead headed after the engine driven pump (mixture is in ICO). Put the mixture full rich for a bit and see if the pressure comes down to 28-32 PSI with the boost pump running. If you have RSA-5 injection, don't leave the mixture full rich to long without the engine running or your will see excess fuel running out the inlet of the air box. If you have Airflow Performance injection you can put the purge valve in the ICO position and you can run the boost pump all day without putting any fuel in the engine.

Engine pump pressure should be 22-26 PSI so your indication is probably a bit high.

Don

RV10Rob · #5 02-13-2011, 11:32 AM

Ah, I see. I do have the mixture in the ICO position, and I have the Silver Hawk system, so no purge valve. I went back and looked at the EMS data from my first engine start, and when priming the system (with mixture full rich) it never got that high.

My thought was that with no flow (in ICO), the relief valve would keep the pressure more or less around 30, but it sounds like valve is designed to trigger at a higher pressure.

Thanks for the help...

-Rob

Don at Airflow · #6 02-13-2011, 12:36 PM

I think I explained this in a previous thread. But since the relief valve poppet seats in a O-ring it takes a bit more pressure to unseat the valve than when it's running. Since there is an outlet check valve in the engine driven pump the pressure gets trapped between the outlet of the engine driven pump and the fuel control when the mixture control is in ICO. Thus if you keep turning the boost pump on and off the pressure indication will creep higher and higher. If you measured the pressure on the inlet side of the engine pump it would read in the 28-32 PSI range.

Don