Fuel Pressure 52psi at idle and gets 0131/0151 only at WOT

[fst100]

1998 LS1 firebird w/LS1 swap A4

currently tripping both B1S1/2 0131/0151 for low voltage. replaced both sensors(previous was i believe bosch) with new ones(bosch 13111) as well as replaced the MAF. only does it at WOT(100%) does not do it below that at any TPS. also whats odd is the ECM won't go into open-loop/power enrichment mode at whatever TPS i have it set in my ECM(tuned via HP Tuners). not even at 80% will the ECM would switch into PE mode.

so i checked the fuel pressure at the rail at idle and it hovers around 52psi. if i rev/blip the throttle it'll drop to 48psi then go back and hover at 52psi again. i havent ran the car at WOT with the fuel pressure gauge yet as its been cold and when i get off work its already dark outside.

fuel pump and fuel filter has ~80k miles. is the closed-loop issue linked to fueling at all?

[Knight]

Your pressure is low. You should see around 58 psi at the rail, with the ignition on and the car not running. Start by changing out the fuel filter.

[fst100]

havent changed the fuel filter yet. i'll do it this saturday. i believe the fuel filter has ~80k because the previous owner said the motor/trans has that amount when he got it from the original owner who did the swap.

[Knight]

Start there, and see if the fuel pressure doesn't raise up to 58 psi. Let us know.

[fst100]

well do, thanks. is there a higher flowing fuel filter over the oem? for example the flex fuel filters from the silverado's as guys from the wbody(grand prix/regal/bonneville) use those over the factory .

[Knight]

Not that I am aware of. There are filters that will filter better than others.

[pajeff02]

Just slap an AC Delco replacement filter on it. The filter is located underneath the car in the area in front of the driver side rear tire. You will need a set of line wrenches and probably pliers to release the clip. Fuel will run and drip from the lines when you disconnect the filter so be prepared and protect your eyes.

[fst100]

okay, got some results-rather bad though....at cruising speed its at ~41-43psi and when i romp on it from 2nd gear the pressure drops and at the top of 2nd gear going into 3rd its at 22-23psi 0_0 im not gonna be doing anymore WOT runs until this is fixed. glad nothing went boom yet.

so what could it be? any suggestions and advice?

TIA guys

[pajeff02]

Filter... pump... regulator... that's about it.

[35th-ANV-SS]

okay, got some results-rather bad though....at cruising speed its at ~41-43psi and when i romp on it from 2nd gear the pressure drops and at the top of 2nd gear going into 3rd its at 22-23psi 0_0 im not gonna be doing anymore WOT runs until this is fixed. glad nothing went boom yet.

so what could it be? any suggestions and advice?

TIA guys

I was going to suggest this.

As Jeff mentioned, I would start with the cheapest thing first; fuel filter. Next would be the regulator. Then, the pump. Sounds like your pump is weak though unfortunately.

[fst100]

alright, i'll change the fuel filter first. to check if its holding pressure should i do a mild 70-80% throttle run and see if it holds pressure or is there another way to check it? i have a racetronix 255lph thats in my wbody gtp car....can i swap the pump from that to the FP assembly in the ls1?

[pajeff02]

Only other possibility would be corroded wiring and/or a faulty connector that has a lot of resistance in it.

[pajeff02]

alright, i'll change the fuel filter first. to check if its holding pressure should i do a mild 70-80% throttle run and see if it holds pressure or is there another way to check it? i have a racetronix 255lph thats in my wbody gtp car....can i swap the pump from that to the FP assembly in the ls1?

Just check it with the key on and then at idle first -- if you don't see 58 psi there then you know the problem still exists.

[fst100]

good point...i'll check back this weekend...thanks

[35th-ANV-SS]

I have a Racetronix fuel pump in my S/C LS1, but I run the performance one which flows more. The 255lph pump on Racetronix's site is recommended for use in LT1's, which I believe has lower fuel pressure than that of the LS1.

Maybe someone else knows.

[fst100]

fwiw, the racetronix pump thats in the GTP handled it when it was turbo'd and trapped many 118mph at the track. i was curious if the pump is any different at all?

if its just simply cutting the assembly to make it fit like in this link:
Installing a Walbro in a 1998 F-Body (Small Write-up) - LS1TECH
then im alright with that. just dont know a whole lot about the fuel pump itself

[fst100]

FWIW, the fuel filter thats underneath the driver side near the rear wheel, i noticed theres one rubber line thats not connected to the fuel filter(fuel filter only has one inlet/outlet) thats coming from the fuel pump side. dunno if thats important or not to mention.