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high fuel pressure

8K views 25 replies 4 participants last post by  BALLSS 
#1 ·
Just installed a Racetronix 255 fuel pump and harness because my old pump was not keeping up at WOT, changed fuel filter as well. The problem I am having is my fuel pressure reads 51psi at prime, 50 to 51 at idle, and when I disconnect the vacuum to regulator the pressure goes up to 54psi, then when I shut the engine off, I loose all pressure in a few minutes. Before I did the swap fuel pressure never dropped off. Could this be the regulator?
Any suggestion would be great.

95 Trans Am Lt1, LE1 head, custom cam, 30# injectors
 
#2 ·
update,
just blocked off the return line and done a prime, fuel pressure went up over 100, and still dropped off, maybe its my cheap fuel gauge? According to my data logs the car is running rich, low blms 104 106 in cell 4, the other cells is not so bad 113-114, 118-119, I also noticed in my log high o2 reading when high, just replaced o2 sensor with AC/delco. Car has a Solomon tune, hes the one who told my the car is starving for fuel at WOT, that's why I changed the pump.

Any suggestion would be great. Maybe I missed up pump connections? Gotta trap door cut.
 
#3 · (Edited)
Your regulator may not be opening enough to bring pressure to normal 43 psi at key on prime and around 36 psi when idling.

Increased fuel pressure means that more fuel is added then needed. Your pcm is calculating amount of fuel to spray using 35-43 psi as it's basis.

When fuel pressure falls quickly after shut down, there are several things that can cause this. Check ball in pump may be defective. regulator stuck open a little bit. Or fuel injector/injectors stuck open. Finally, leak at where fuel hose attached to fuel pump.

Since pump only has positive & negative wires to hook up, don't know if that is your problem. If you hooked pump up backwards, It would run backwards. I've never tested the output of a fuel pump running backwards to know what effect it would have on fuel pressure.

But my guess is, it would pump fuel away from fuel rail back to tank, if pump leads reversed.
 
#4 ·
I just took out the pump again, all the hoses are hooked up right, pump as about 50km on it, hope its not check ball in pump, I fitted a old 96 Corvette regulator on my fuel rail just for test and had the same results. I order a new regulator but it won't arrive for another 10 days. Yesterday morning I done a pressure test before the new pump install, I had 42 psi on prime and it stayed pressurised, only thing I never checked when I removed the pump was positive and negative feed to pump. Guess its out with the pump again.
 
#5 ·
One more thing, engine runs good, if I never had my laptop plugged in, I would never no there was a problem except for hard starting due to fuel pressure bleeding off.
 
#6 ·
with your raceTronix kit it may be necessary to run a adjustable FPR to set the FP where it needs to be

your rich readings and high 02 counts are because your FP is to high. The PCM can not compensate for it that high

you can buy a adjustable FPR at some auto part stores. I got mine at Advanced Auto. BWD (borg warner) # 23065. direct fit
 
#7 ·
I only got the 255LPH pump and harness, says stock replacement, did not read anywhere when ordering that pump that I needed a adjustable regulator. Did your pump do the same with stock regulator, high pressure and bleed off quick. Kinda like to no for sure before I order more parts.Pretty much got my car budget used up for this year lol.
 
#8 ·
I don't have a RaceTronix kit. I do have a Walbro 255 pump though which does put out more than the stock pump but I didn't have high FP with a stock FPR as a result. The pressure does bleed off in about 10 min once I shut down

For whatever reason your stock FPR is not stabilizing the pressure.

I can't remember how much $ my adjustable was, IIRC around $55. I bought it when my original FPR started leaking fuel into the rubber vac line. $ for Delphi, AC Delco, etc are around $40-$80 for a standard replacement FPR on rockauto.com

IMHO stay away from Aeromotive

While my tune is based on stock FP, I use the adjuster screw to put it dead nuts there. If you turn the pressure up you can see the 02 readings start to read high and ST & LT fuel trims change so to much pressure is going to negatively affect the car as PCM can't compensate for it. You will run rich as a result of to much FP
 
#9 ·
My regulator is not leaking Not that I can tell. Guess I might as well order that adjustable one. The stock one I ordered is about 130$ Canadian Hopefully I can get my deposit back. Thanks for your input.
 
#10 ·
your FP readings by your gauge is high and the data of the 02, etc are high so your Racetronix FP is faulty causing higher FP or your regulator is not adjusting it correctly.

You don't need a adjustable but for me it was the same $ range as a standard and is plug & play install as it is the same size/shape as stock one. It was available at 2 large chain auto part stores here (Advanced auto & o'rielys). IDK what you have in Canada....but the beer is better there :)

Your in Canada...so I see why you went RaceTronix. Might want to contact their tech line and ask.
 
#11 ·
Beer is pretty good here, I drink Canadian Budweiser, I think that's half my problem. I did email racetronix to see what they have to say. I will report back about customer service.
 
#13 ·
I did get a reply from them after I joined there tech page, there saying that I got a return restriction. Never had one before, but I guess I will take the pump out for the forth time and check it out. Good job I when the trap door route.
 
#17 ·
got it, thanks. so RaceTrnix is saying a restriction in the return line...odd the original pump FP was good. Op puts in RaceTronix pump and has problems. I would suspect the problem is pump......unless somehow in the process of install the return line became "restricted"...if I understand RaceTronix is saying the Ops return line is the issue and not their pump.
 
#16 ·
a pump can't really be the cause for over-pressure, unless it's providing so much fuel volume that the regulator or return line becomes a restriction point (with a traditional single pump setup, i doubt it)

i had a regulator that gave me like 50psi once too. swapped regulator, problem solved. pulled the regulator apart and the vacuum side of it was all green and shitty, so it was probably sticking.
 
#18 ·
Pretty much all I got from them was that my return line was restricted. They give me a link which showed how to open up the return line fitting on the bucket.
 
#19 ·
Update:
Still waiting on new regulator to show up but in the mean while everyday for the past week I have been doin fuel pressure testing and yesterday something changed, after disconnecting the vacuum line off and on at idle a few times in a roll I noticed the pressure is holding now. No more hard starting, starts right up first try. I still have 50 psi on prime for 2 or 3 seconds then drops to 42 but at idle I still have 50 psi but when I rev the motor a little it drops to around 42 psi, I noticed at idle when I disconnect the vacuum of the regulator my pressure rises to 52-54 psi. I'm not sure but thinking it's my regulator. Anyone out the have any thought?
I can not do a driving test because my gauge line is to short to be taped on my wind sheld.
Thanks.
 
#21 ·
Another update:
One problem solved, new regulator fixed high pressure, now I have 46 psi on prime, 43 at idle but pressure slowly bleeds off in about hour. Checked injectors, seems to be good but I do get a hint of raw gas when driving sometimes. Not sure when its coming from. One thing about it, this old car is keeping me busy.
 
#23 ·
I no I have a exhaust leak after my LT headers into my Y pipe, that would be right under my driver seat, every time I smelt gas I got out and popped the hood and smelled around but nothing, I only smelt the gas when motor was hot. I guess it could be coming from my trap door, no door installed yet just carpet pulled over the hole.
 
#26 ·
I no I have a exhaust leak after my LT headers into my Y pipe, e.
if this exhaust leak is upstream of your 02 sensor...it will read lean because it sees air and PCM will command fuel which means you will run rich on that bank. You can FU a CAT that way which will clog it and cause even more havoc.

not sure if the gas smell is from running rich or from your fuel pump hole you made...either way you should not smell "gas" inside the car
 
#24 · (Edited)
Fuel pressure bleeding down after a hour is normal and nothing to worry about.

You might want to put your car on an obd 1 scanner that does real time sensor data. A very rich air/fuel mixture would give the smell of gas also.

If you don't have an obd 1 scanner here's a link to the obd 1 scan program called "scan9495" It scans for regular codes, ABS & SIR codes. It does running sensor scans and will log data to a file for later playback.

It also tests engine & auto trans actuators. And it's free. Get at www.mediafire.com/?0elo4c935uc5s

You will need a 16 pin obd 1 cable to connect car's aldl to usb port of pc based computer. get at
www.aldlcables.com
 
#25 ·
It was running rich, right now I am unable to scan, I either need a new laptop battery or power inverter, It was always richer on driver side. switched injectors from side to side but nothing changed, also changed o2 from side to side, still rich on driver side, It was related to high fuel pressure some what, thinking if everything was running right should of been evenly rich on both sides. when I get scanning again I will post results. Thanks for all the feed back.
 
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