Tirefire

iTrader: (1)

I was told by Bob, at EPP that my fuel pressure should always stay at 60-58 psi. I don't know if that was at idle or during boost?? I only ask because today I was driving around and decided to get on it and for some reason looked to my fuel pressure and observed that it was at about 50 psi and I think I was at about 6-7 lbs. of boost. I let off and didn't want to mess around until I could get some answers.. Could someone plese let me know if that is normal or do I have issues I need to fix. Thanks Andy

navymitch12

iTrader: (1)

i am by no means an expert but i would say that is ok....

becuase under boost you are using a lot more fuel so the pressure would go down becuase the pump pumps basically the same volume at all times...

just what i am thinking

Tirefire

iTrader: (1)

Yea, I was thinking the same thing. I just got confused when Bob told me this... I do remember reading about this on turbobuick.com, but like I said I just got a little confused... I guess I can always call him him and clearify this.. thanks

DeltaT

iTrader: (5)

Is your fuel pressure regulator referenced to your boost at all? I'm thinking that your pump is not keeping up, because your fuel pressure should rise 1:1 with your boost psi. If your normal fuel pressure is 58 and you're running 8.5#, then your boosted FP should be 66.5psi. Or maybe you're not running an AFPR?

Jim

SStolen

iTrader: (22)

If that was the case, then that would mean his fuel pressure would stay at 58psi without a boost referenced FPR under boost. Instead, it is falling 8psi or so. If it was boost referenced, if anything, his pressure would simply STAY at 58psi at WOT to compensate for the drop-off.

Mine falls from 58/59 at idle to 50/51 when under boost except I am running about 18lbs. I too was wondering if this was ok. We could just both be messed up but I think this is ok. Plus, I'm pretty sure the person who tuned my car would have noticed and said something to me. The air/fuel is the same as it was when it was tuned so it is def. the same fuel pressure as before. Take it for what you will.

Boostaholic

iTrader: (4)

I run 43 + Boost PSI, so 43 at idle, 52 on full boost

gametech

iTrader: (1)

Not to be a smartass, but someone with the experience of Bob at epp gives you advice and you have to question it on the internet? Just to clarify, if you have a non-adjustable regulator, your fuel pressure should stay the same always. If you have a boost referenced regulator, your fuel pressure should rise at a rate of 1=1 with boost pressure or drop at the same rate with vacuum. If your fuel pressure drops below this, you need a more adequate fuel supply.

edit- sorry if I misread the intention of the original post

MECHAM

iTrader: (4)

yr running out of pump flow

Tirefire

iTrader: (1)

gametech, I'm not questioning Bob, I'm only wondering if he meant it should stay at 58 psi during boost. I simply forgot to ask him when he told me. Please don't come in here and try to manipulate a simple question!!

Jake@EPP

The pressure should remain around 58-60psi at idle, it will dip a little down under boost as the pump needs to work harder to maintain pressure.

Tirefire

iTrader: (1)

Thanks Jake, what do you think my promblem is bud???I have a BAP so do you think it could be that??

Jake@EPP

I dont belive it could be the boost-a-pump as if that would die you would seriously drop pressure.

Tirefire

iTrader: (1)

I guess I can always try the pump. Do you think that the pump is getting enough amps. I read that sometimes at wide open throttle the pump sometimes doesn't get enough power??

Tirefire

iTrader: (1)

Alright guys I went and filled the tank just to illiminate the possibilites that I might be starving the fuel pump, but when I got on it the fuel pressure still went down. Kind of bummed about that, but I still ended up getting a great kill out of it!!!! I'll post about that in the kill stories forum... Thanks Andy..

MECHAM

iTrader: (4)

u need more pump flow...

Redline-Motorsports

iTrader: (3)

Ideally the pressure shouldn't drop more then 5 psi on boost. However if the AFR under boost is good and the injectors are under 80% DC, it really isn't a big problem. Bottom line is the final AFR under all load conditions. Personally I'd upgrade the fuel system, but I don't think you have a major problem if the AFR is solid.

JMBLOWNWS6

iTrader: (17)

I run mine @ 58 at idle. With the fuellab referenced 1:1 and it goes up to about 72 psig under wot. My fuel pressure is rock solid unreferenced also. But I dont have a stock fuel system either.

DeltaT

iTrader: (5)

The reason you want an AFPR with a 1:1 rise in pressure is that when you start making boost the injectors have a resistance in psi equal to your boost that they have to overcome to squirt. If your FP is at 58 with no boost referenced regulator, and you are boosting 10#, then the effective injection pressure will be 48psi, at the exit of the injector. Your rail could still show 58, but it would probably be lower. If you exaggerate the numbers a little and imagine making 58 pounds of boost along with your stock 58psi FP, then when the injectors opened, nothing would come out, because there is only flow from a high pressure zone to a low pressure zone.

As someone above already said, and you seem to be tuned for, some pressure drop can be dealt with (tuned around) but it is not the optimal setup.

Also, in an unregulated fuel pressure setup, like if you just have a return restricted orifice, your system fuel pressure would drop under boost because a lot more of the fuel is leaving the rails and entering the engine, ie. there would be less of a restriction seen at the engine end of the fuel system, so pressure would drop. Just like taking your thumb off the end of the hose, flow rises, pressure drops.

Jim

EPP

iTrader: (22)

Andy, with your fuel system you should have 58 to 60 psi at idle. It is normal for it to drop to approx 54 psi under boost.
Andy Toscano has a 2000 Trans-Am that he had shipped up to us from his home in El Paso, Texas. Andy had us install a Lingenfelter GT2-3 camshaft, a new timing chain and oil pump, pushrods and valvesprings. Topping all of this off was a new ATI ProCharger D-1SC.
Andy wisely had us install a Spec Stage 3+ clutch and pressure plate and a new flywheel while we were at it, along with a Moser 9 inch rear-end with 3.70 gears and a Truetrac center section.
Here is a link to Andy's car. http://www.exoticperformanceplus.com/hotCars.php?car=62
Bob

Tirefire

iTrader: (1)

Thanks Bob I'm going to keep monitoring my fuel a little longer it seems as if it might be going just under 54 psi. The day before yesterday was the first time I actually saw my fuel gauge I'm usually to busy looking at the road with all this new power to even look over at my gauges. haha