Fuel Pressure Drops Under Boost

1999ssls1 · 10-06-2009, 01:40 PM

I am running 10lbs of boost with a base pressure of 60 psi. I have boost referenced FPR, so It goes to 70psi under boost but drops to 50psi around 4800rpms and stays there. Car is making around 600rwhp. This is driving me insane because I cant get my car tuned until I fix this on going issue. Any help greatly appreciated.

Fuel Setup Is:

Dual walbro 255s intank
Pro Products FPR
8AN feed 6AN return
60lb Mototron

First pump is hotwired with ignition and second on a toggle. Both have 13.4 volts. Do you think it could be my FPR? Also I just replaced my pumps.

STAR · 10-06-2009, 02:41 PM

How is the second pump activated? What do mean by toggle switch? If you can confirm both pumps are coming on then I would suspect faulty regulator.

1999ssls1 · 10-06-2009, 03:27 PM

Yes a toggle switch. Both are working for sure.

Old Geezer · 10-06-2009, 09:02 PM

"Also I just replaced my pumps."
Confirm that there's not an intank leak.....Even if both are running, and there's a leak, the remaining flow may not be sufficient to maintain FPR setting...

1999ssls1 · 10-06-2009, 10:14 PM

I also replaced the hoses in the fuel pump assembly.

Lonnies Performance · 10-06-2009, 11:29 PM

The hoses are likely the problem.. especially if you used rubber ones.

You also did not state your regulator setup & how it is plumbed?

The dual intank setup, if built properly, should be able to hold steady pressure at the max flow capacity of the 60# injectors.

1999ssls1 · 10-07-2009, 12:21 AM

I just installed new rubber 5/16 hoses. Profesional products boost referenced fuel pressure regulator.

1999ssls1 · 10-07-2009, 05:27 PM

I am running 5/16 rubber fuel hose with a T fitting.

koolaid_kid · 10-07-2009, 08:30 PM

Did you use the submersible fuel line? (I believe it has to meet SAE 30R10 standards.)
Gates Hose # 27093 is the 5/16" ID submersible hose, SAE 30R10 spec.
It should have cost you ~$18-$20/foot. Although I prefer the flex hose my Racetronix kit came with. Apeusa sells it, not sure if they are a sponsor though.

1999ssls1 · 10-07-2009, 09:48 PM

Yes I did.

craig382ci · 10-09-2009, 01:19 PM

I have a friend that had the same happen to him. With the same parts you have for your set up. I dont know what all he tried b4 he pulled everything off and replaced all lines, pumps and FPR even though it was all new. After he put it all back together for the 2nd time it worked fine. Sometimes even if you have the best of everything, they still shouldnt be put in the it's ok box. Because it's new and the best and done right. doesn't mean it's ok to rule out as a problem.

I dont know if they are away to pressure test the lines. But if they are away I would have each one tested or just get all new again and redo it. But it's those unseen things that gives the most troubles. Like a small pinhole in a brand new line that was over looked. Or something wrong with one of the pumps ect. Just because you couldnt/didnt see it or that it is all new. Dont rule it out. Not saying that is your problem. But you never know until you try! I can say this. Even though they was nothing visible to the eye on my friend's setup. It was something to do with it. He sold it all to someone and it did the samething on that man too. I would replace the cheapest stuff first and go from that. Just for the fact I have more time than money to waste.