Startup fuel pressure problem
Thread Starter
Le Mans Master
Joined: Feb 2003
Posts: 9,087
Likes: 0
From: Chicago IL
Startup fuel pressure problem
The fuel pump and filter on my 94 are new. I attached a F/P gauge with the engine cold and noticed there is almost no pressure until I have tried cranking the motor a few times. The engine starts, stumbles and the pressure is in the mid 30's at idle and mid 40's with the vacuum line off. The oil pressure switch was also just replaced.
Should the pump be priming when the key is turned?
Should the pump be priming when the key is turned?
Pro
Joined: Jul 2002
Posts: 524
Likes: 1
From: Port Charlotte Fl
The fuel pump and filter on my 94 are new. I attached a F/P gauge with the engine cold and noticed there is almost no pressure until I have tried cranking the motor a few times. The engine starts, stumbles and the pressure is in the mid 30's at idle and mid 40's with the vacuum line off. The oil pressure switch was also just replaced.
Should the pump be priming when the key is turned?
Should the pump be priming when the key is turned?
Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
Yes, pump should be priming (~2 seconds with the key in "run" without cranking) and when the key is in the "start position" , the pump should supply pressure to the fuel rail and beyond.
Check your bleed down times.....could have a injector/s stuck open....bad pressure regulator....bad pump...or bad pulsator module.
Good Luck!
Check your bleed down times.....could have a injector/s stuck open....bad pressure regulator....bad pump...or bad pulsator module.
Good Luck!
Thread Starter
Le Mans Master
Joined: Feb 2003
Posts: 9,087
Likes: 0
From: Chicago IL
Yes, pump should be priming (~2 seconds with the key in "run" without cranking) and when the key is in the "start position" , the pump should supply pressure to the fuel rail and beyond.
Check your bleed down times.....could have a injector/s stuck open....bad pressure regulator....bad pump...or bad pulsator module.
Good Luck!
Check your bleed down times.....could have a injector/s stuck open....bad pressure regulator....bad pump...or bad pulsator module.
Good Luck!
Melting Slicks
Joined: Jan 2008
Posts: 2,514
Likes: 30
From: Friendswood TX
I am watching this post as i am having some fuel issues (so i think) with my 96 LT4.
My fuel pump does NOT prime when the key is turned on. I had some issues with the way the car ran and the way it would start leading up to the car finally crapping out on me so im lead to believe i had a pump on the frits that finally gave out on me. I dont have a fuel pressure guage. I need to get one but that fact that the pump doesnt prime is enough to tell me the pressure wont be there.
Any other ideas as to what my problem could be?
Could my problem on my 96 also possibly be injector/s stuck open, bad pressure regulator, bad pulsator module or bad relay or pressure switch?
My fuel pump does NOT prime when the key is turned on. I had some issues with the way the car ran and the way it would start leading up to the car finally crapping out on me so im lead to believe i had a pump on the frits that finally gave out on me. I dont have a fuel pressure guage. I need to get one but that fact that the pump doesnt prime is enough to tell me the pressure wont be there.
Any other ideas as to what my problem could be?
Could my problem on my 96 also possibly be injector/s stuck open, bad pressure regulator, bad pulsator module or bad relay or pressure switch?
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Thread Starter
Le Mans Master
Joined: Feb 2003
Posts: 9,087
Likes: 0
From: Chicago IL
It is weird because it takes a few tries before the pump registers any pressure. Then, pressure is fine and car runs as it should.
The right bank lean condition is obviously a fuel problem and can either be a fuel rail blockage or a clogged injector since the pulses are fine.
I am going to run a can of seafoam and see if maybe that clears it out.
I am stumped on this startup pressure problem, though.
The right bank lean condition is obviously a fuel problem and can either be a fuel rail blockage or a clogged injector since the pulses are fine.
I am going to run a can of seafoam and see if maybe that clears it out.
I am stumped on this startup pressure problem, though.
Melting Slicks
Joined: Feb 2008
Posts: 3,286
Likes: 6
From: Palm Beach
I see you started your own thread. Jumping into someone else's confuses the issue.
I am watching this post as i am having some fuel issues (so i think) with my 96 LT4.
My fuel pump does NOT prime when the key is turned on. I had some issues with the way the car ran and the way it would start leading up to the car finally crapping out on me so im lead to believe i had a pump on the frits that finally gave out on me. I dont have a fuel pressure guage. I need to get one but that fact that the pump doesnt prime is enough to tell me the pressure wont be there.
Any other ideas as to what my problem could be?
Could my problem on my 96 also possibly be injector/s stuck open, bad pressure regulator, bad pulsator module or bad relay or pressure switch?
My fuel pump does NOT prime when the key is turned on. I had some issues with the way the car ran and the way it would start leading up to the car finally crapping out on me so im lead to believe i had a pump on the frits that finally gave out on me. I dont have a fuel pressure guage. I need to get one but that fact that the pump doesnt prime is enough to tell me the pressure wont be there.
Any other ideas as to what my problem could be?
Could my problem on my 96 also possibly be injector/s stuck open, bad pressure regulator, bad pulsator module or bad relay or pressure switch?
Melting Slicks
Joined: Jan 2008
Posts: 2,514
Likes: 30
From: Friendswood TX
It is weird because it takes a few tries before the pump registers any pressure. Then, pressure is fine and car runs as it should.
The right bank lean condition is obviously a fuel problem and can either be a fuel rail blockage or a clogged injector since the pulses are fine.
I am going to run a can of seafoam and see if maybe that clears it out.
I am stumped on this startup pressure problem, though.
The right bank lean condition is obviously a fuel problem and can either be a fuel rail blockage or a clogged injector since the pulses are fine.
I am going to run a can of seafoam and see if maybe that clears it out.
I am stumped on this startup pressure problem, though.
Im throwing a right bank code on mine and it came out as High voltage o2 on the right bank. Just wondering if thats the same code you got?
Last edited by WickedVetteLT4; Sep 2, 2008 at 07:12 PM.
Melting Slicks
Joined: Jan 2008
Posts: 2,514
Likes: 30
From: Friendswood TX
Im not trying to confuse anyone or jack the thread by any means. Just trying to figure out what to consider as a possible problem on my car and it seems him and I are having the same problem.
Melting Slicks
Joined: Feb 2008
Posts: 3,286
Likes: 6
From: Palm Beach
Thread Starter
Le Mans Master
Joined: Feb 2003
Posts: 9,087
Likes: 0
From: Chicago IL
44 - lean exhaust
48 - MAF
43 - knock sensor
I am starting to think it is a MAF problem because the motor runs way better with it unplugged and struggles and detonates with it plugged in.
Melting Slicks
Joined: Jan 2008
Posts: 2,514
Likes: 30
From: Friendswood TX
I was told to consider the MAF on my car as the problem. It wouldnt start with or without it plugged in so it made no difference on mine. If yours is acting up when its plugged in but runs fine with it unplugged, i would guess thats your problem.
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
This obviously is the initial starting point. Also make sure the relay is properly seated and you might check the pins for any corrosion.
Thread Starter
Le Mans Master
Joined: Feb 2003
Posts: 9,087
Likes: 0
From: Chicago IL
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
Don’t have my FSM with me at this time so this is just an opinion from what I remember. There are 3 relays in a row on one block under the spedo to the left of the steering column as viewed as if you sitting in the seat. Kind of in line with your left knee up underneath. It is not the relay on the right, but can’t remember if its on the left or the center one.
That’s the area, perhaps someone might jump in today with the exact location, if not I will put it in tonight.
That’s the area, perhaps someone might jump in today with the exact location, if not I will put it in tonight.
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
Don’t have my FSM with me at this time so this is just an opinion from what I remember. There are 3 relays in a row on one block under the spedo to the left of the steering column as viewed as if you sitting in the seat. Kind of in line with your left knee up underneath. It is not the relay on the right, but can’t remember if its on the left or the center one.
So much for memory. According to the FSM, its on the right side if front of the passenger. Mush more difficult to get to and explain. Its by the cruse control module to the left of it, looks like inside of a box with other relays. Top cover comes off and looks like FP relay on the far left.
To get there, lower trim panel has to come off, floor air outlet and not exactly sure what else since I have not looked for the relays myself. Been in there but not for that and been a few years. Don’t have a PDF or pix to put in here. Good luck if you need to go there.
