Fuel pressure question
Thread Starter
Drifting
Joined: Jul 2001
Posts: 1,296
Likes: 0
From: Largo Florida
Fuel pressure question
I was looking at the fuel pressure gauge after doing an adjustment and noticed that when I turn off the car the pressure drops at a rate of 10psi every 20 seconds. I don't recall it doing that before. I heard that is an indication that I have leaky fuel injectors. Is that correct?
[Modified by ericcer, 8:50 PM 12/18/2002]
[Modified by ericcer, 8:50 PM 12/18/2002]
Safety Car
Joined: Feb 2002
Posts: 4,212
Likes: 10
From: Sun City West Az
Re: Fuel pressure question (ericcer)
Not necessarily. It shouldn't go to "O" in a few minutes. It should however, fall and maintain a pressure around 20 psi. Eventually it will fall to "O". If it held pressure near the top, there would be no need for the fuel pump to run and prime the system for 2 sec. before start up. All this info. via Rich @ cruzin performance (the injector guy) because I asked him the same question. :D
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,009
From: Texas
Re: Fuel pressure question (ericcer)
I was looking at the fuel pressure gauge after doing an adjustment and noticed that when I turn off the car the pressure drops at a rate of 10psi every 20 seconds. I don't recall it doing that before. I heard that is an indication that I have leaky fuel injectors. Is that correct?
- Pull the fuel rail from the intake with the injectors connected to the fuel rail. Turn the key to "Run" but don't crank the engine (obviously :) ). If the injectors are leaking, you'll see the fuel coming out of whichever one(s) are bad. It's ok if there's residual dampness, but they should not drip
- To check the fuel pressure regulator, pull the vacuum hose off of it. If it's bad, fuel will be in the vacuum hose
- If none of the above occur and your fuel pressure bleeds down quickly as you state it's doing, it's likely the fuel pump check valve is bad or the fuel dampener bad.
In the Factory Service Manual, Book2; Section 6-311 Fuel System Diagnosis, there's a rather lengthy procedure to follow.
Thread Starter
Drifting
Joined: Jul 2001
Posts: 1,296
Likes: 0
From: Largo Florida
Re: Fuel pressure question (96GS#007)
Well I have a new adjustable fuel pressure regulator. I removed the fuel rail before I did that test a month ago with no drips. I remember the pressure guage used to hold pressure much better and longer than that.
Where or what is the fuel dampener? Part of the fuel pump? Would that cause any driveablity problems? I have been chasing a bad idle and cutout problems for months.
[Modified by ericcer, 5:59 AM 12/19/2002]
Where or what is the fuel dampener? Part of the fuel pump? Would that cause any driveablity problems? I have been chasing a bad idle and cutout problems for months.
[Modified by ericcer, 5:59 AM 12/19/2002]
Race Director
Joined: Apr 2000
Posts: 15,344
Likes: 4,009
From: Texas
Re: Fuel pressure question (ericcer)
Where or what is the fuel dampener? Part of the fuel pump? Would that cause any driveablity problems? I have been chasing a bad idle and cutout problems for months.
A leaky check valve or dampener can cause driveability problems like you're having.
Before dumping the $$, I'd run through the diagnostic procedure in the Service Manual. A leaky dampener is unusual. I'd say a bad fuel pump is unusual too...except I had one fail in my old '90 and one my GS. Idle was fine, but they both exhibited a pretty significant stumble going from steady state cruise to WOT or "significant" acceleration.
Safety Car
Joined: Feb 2002
Posts: 4,212
Likes: 10
From: Sun City West Az
Re: Fuel pressure question (ericcer)
Where or what is the fuel dampener? Part of the fuel pump? Would that cause any driveablity problems? I have been chasing a bad idle and cutout problems for months.
The dampener is a check valve and part of the pump asym. To check the pump and dampener, hook up the guage on the schrader valve, key on. engine off; (your guage should show pressure), clamp off fuel supply line at the top of the tank. If the pressure holds, the pump / check valve is bad.
