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View Full Version : car starting problem HELP ASSSAPP loosing fuel pressure


grass disaster
06-15-2007, 11:38 PM
1996 cutlass supreme sl

3.1 liter


having problems starting, runs good once started.

hooked up to fuel pressure gage.

turn key has good pressure when fuel pump activates(goes up to 40). as soon as i hear the fuel pump stop it drops pressure, goes to about 5 - 0 psi.

why am i loosing pressure?? it has pressure once it starts about 35 psi

p.s fuel pump was replaced little over 1 year ago

Restrorob
06-16-2007, 12:38 AM
If it pumps 40 lbs. when you turn the key on do you wait for the pump to stop before you turn the key to crank it up ?

Have you checked for any fuel leaks possibly around the fuel filter or any steel lines ?

grass disaster
06-16-2007, 12:45 AM
If it pumps 40 lbs. when you turn the key on do you wait for the pump to stop before you turn the key to crank it up ?

Have you checked for any fuel leaks possibly around the fuel filter or any steel lines ?

i didn't see any leaks

if i time it right to crank it just before the pump stops it will start, if i try crank it right away or wait 2 sec after it stops pumping it won't start cause it has no pressure.

Restrorob
06-16-2007, 08:12 AM
Does your fuel rails look like these;

http://i107.photobucket.com/albums/m314/Restrorob/FuelRail.jpg


If so (my manual only goes to 95) then it may be possible the fuel regulator #7 is acting up, But remember I've been out the biz for some time now and just throwing things.

grass disaster
06-16-2007, 10:37 AM
Does your fuel rails look like these;

http://i107.photobucket.com/albums/m314/Restrorob/FuelRail.jpg


If so (my manual only goes to 95) then it may be possible the fuel regulator #7 is acting up, But remember I've been out the biz for some time now and just throwing things.

well here is a picture of it.

it starts fine when motor it is cold

i thought i had the fuel regulator replaced but it doesn't look very new??

Restrorob
06-16-2007, 07:07 PM
Yeah, It does look like that ones been on there a little while. You may check that plastic line and make sure it's not broken anywhere (out of sight). You may be able to put a short piece of vac. hose on the regulator and suck on it to see if it's holding a vacuum if you don't have a Mighty-Vac tester.

Also, By the looks of that engine the under side of the body must have rust on it also. I have replaced quite of few rusted brake lines on northern cars, The brake lines and fuel lines are run together under the body. The coils wrapped around the brake lines would transfer the fluid down the line instead of dripping on the floor.

I'm just saying, Check the fuel line closely for any wet looking areas because it could have a small pin hole and evaporating before showing a puddle on the floor.

grass disaster
06-17-2007, 03:56 PM
Yeah, It does look like that ones been on there a little while. You may check that plastic line and make sure it's not broken anywhere (out of sight). You may be able to put a short piece of vac. hose on the regulator and suck on it to see if it's holding a vacuum if you don't have a Mighty-Vac tester.

Also, By the looks of that engine the under side of the body must have rust on it also. I have replaced quite of few rusted brake lines on northern cars, The brake lines and fuel lines are run together under the body. The coils wrapped around the brake lines would transfer the fluid down the line instead of dripping on the floor.

I'm just saying, Check the fuel line closely for any wet looking areas because it could have a small pin hole and evaporating before showing a puddle on the floor.


but if it's a leak i would think it would have a hard time starting when the motor is hot and cold.

Bill Kapaun
06-17-2007, 06:03 PM
I can't speak specifically for GM, but-
Does this FI system have a return line to the tank?
IF so, there should be a pressure relief valve somewhere in the system that maintains pressure on the fuel rails, but allows excess fuel to recirculate back to the tank. It's probably part of the fuel pressure modulator.
I would expect your problem to be there.

grass disaster
06-17-2007, 07:14 PM
I can't speak specifically for GM, but-
Does this FI system have a return line to the tank?
IF so, there should be a pressure relief valve somewhere in the system that maintains pressure on the fuel rails, but allows excess fuel to recirculate back to the tank. It's probably part of the fuel pressure modulator.
I would expect your problem to be there.


is fuel pressure modular the same as the fuel regulator?

what you said would make the most sense i just need to know where or what part does this.

Bill Kapaun
06-17-2007, 10:39 PM
Yes- I meant to say regulator:o

As I mentioned, I'm not very well versed in what you have. Look where a return line goes back to the tank.

grass disaster
06-18-2007, 01:23 PM
how do i block the return line?

my mechanic thinks it's in the fuel pump somewhere. he said block the return line if it still looses pressure then you know it's in the pump.

Bill Kapaun
06-18-2007, 04:29 PM
Just a WAG!
If it screws in with some kind of "standard" fitting, you should be able to find a "pipe plug" somewhere?
Who knows what thread, metric or NPT or? Maybe a GM mechanic would know??

lucforce
06-22-2007, 01:12 AM
There is a check valve in the pump itself. Get a new fuel pump and your problem will go away.

69lt1bird
06-22-2007, 10:13 AM
You don't really block the return line, you actually restrict it by squeezing it with a pair of needle nose pliers. The fuel pump is the most likely problem.

Green Grass
06-30-2007, 05:10 PM
Gm runs a fuel pressure regulator on the fuel rail that has the job of keeping the pressure in the rail it is the pumps job to get it there is while the pump is running there is fuel pressure then the pump works fine and unless you have fuel leaking on to the ground or into a cylinder then it is the regulator that is not holding pressure. It is a very common part on a GM if you pull off the vacuum hose on the regulator and you will probley see fuel coming out if you have more questions feel free to PM me