jclayc

iTrader: (8)

Hi - I've developed a fuel pressure issue when my car is running maybe you can give me some thoughts on the cause. I have a 2005 LS6 CTS-V with a Racetronix pump in the tank + hotwire kit. The in-tank FPR has been removed and replaced with a barbed fitting and submersible hose up to the top of the fuel bucket where the return line comes in. The return-style fuel filter has been replaced with a "normal" one. Fuel goes to Holley rails through the stock line, out the back of the rails to an FPR then back to the tank via a -6 AN return line. I have a fuel pressure gauge on front of the driver's side rail. Injectors are 63lb Deka units.

I had the car tuned with this setup and for a few months, my static and running fuel pressure was 60 psi. Now, I can turn on the key and it pressures up to 60psi. When I start the engine, it goes up to 80psi. Trying to adjust the FPR seems to do nothing at all - all this is true of my original Fuelab FPR and a new Aeromotive FPR I have. Any ideas on a cause? Higher pressure tells me perhaps a kink somewhere or blockage but wouldn't that cause the static pressure to go up as well? Thanks in advance for your thoughts!

Part of me says, well, duh, the pressure goes up when the car is running - just reduce the static pressure and the running pressure will be fine. But, as I say, it was fine at 60 both static and running for a while and it doesn't seem like adjusting my FPR does anything either static or running...

JRENIGAR

iTrader: (37)

Does air pressure build up in the tank like maybe the purge valve is not working? Try removing the gas cap then start it up and check the pressure.

soundengineer

iTrader: (16)

just a thought....
but does it also go up if you put a battery charger on the car on the high amperage setting?

I've seen a dying/old battery not put out enough voltage when sitting still
and as soon as the car is running and spinning the alternator it has plenty of voltage and the fuel pressure goes up.

jclayc

iTrader: (8)

JRENIGAR - good thought on relating this to a possible purge valve/EVAP issue. I've been trying to track down a gas smell (no leaks) recently. I think I solved that issue with a new gas cap. That's the only thing that's changed in the recent past. Coincidentally, I have the rear cradle out this morning for another project and replaced the EVAP canister & purge valve this AM because I could do it easily. Once I get everything put back together, I'll let you know what I find.

soundengineer - I'll give it a try, as my Optima red top has lost its charge twice in the recent past. The battery is less than a year old but perhaps it's related. The thing is, if it was electrical in nature, why wouldn't adjusting the FPR make any difference when the car is running?

soundengineer

iTrader: (16)

sorry, I missed the part about the FPR.....

it does sound like you have a 2 part issue there...

your pump should be able to supply the same pressure if the car is running or not...

so you may still have a voltage issue...

but the fact that the FPR doesnt make any difference sound like either you have a broken FPR(maybe a broken diaphragm), or a clogged Vent somewhere

does the FPR use a vacuum reference? or does it have a vent to atmosphere port? or neither?
does your fuel tank have a vent? does it have an evap system with a charcoal canister?(they often clog up)

jclayc

iTrader: (8)

my first thought was the FPR being bad but it does the same with a brand new aeromotive FPR, so the FPR is effectively eliminated as a suspect.

yes, there is a canister with a purge valve up above the fuel tank that I replaced this morning. Perhaps that will be the solution. I changed the EVAP solenoid in the engine bay a week or two ago...

yes, there is a reference port on the FPR. I have it venting to the air right now but could connect it to the back of my FAST 92...

JRENIGAR

iTrader: (37)

My thoughts on it were: if there is tank pressure that would make fuel easy to pump to the rails but hard to get back to the tank causing a rise in pressure when the pump is running and circulating fuel. Kind of like taking a gas can to the station to fill it up, its always ready to burst by the time you get back home with it because of gas sloshing around in it. When the gas cap was leaking and giving off a smell that could have been enough to allow the fuel back into the tank without causing a rise in tank pressure. When you replaced it then the problem should have started from there.

jclayc

iTrader: (8)

well, shoot - started things back up this AM with a new EVAP canister and the fuel cap off and it still goes up to like 85psi when running, with the FPR adjustment seeming to make no difference while running. i guess it's got to either be (for some reason) having the alternator providing charge causes the fuel pump to increase pressure or something is going on in the tank with the pump/bucket/lines/. If it's the former, I wonder why it's suddenly doing this and how to prevent it?

Although it shouldn't make a big difference, perhaps I'll try hooking up the reference port and seeing what happens before I start digging back into the tank.

jclayc

iTrader: (8)

closing the loop on this one - a kink had developed in the return line inside the tank. I replaced the submersible hose with a fuel tube from Racetronix and I'm good to go. http://racetronix.biz/items.asp?Cc=T...atus=0&Tp=&Bc=

JRENIGAR

iTrader: (37)

Glad you posted back with what the problem was.