Mechanics

CHEVY FUEL PRESSURE

1996 Chevrolet Tahoe

Engine Performance problem
1996 Chevy Tahoe V8 Four Wheel Drive Automatic 220000 miles

1. What should the fuel pressure be when the key is turned on, motor not running.
2. What shoulg the fuel pressure be with the motor running.
3. Does the fuel pump stop running with the key in the on position engine not running after it builds pressure in the system

I have no codes, no miss fires show on hand held scanner, truck sputters going down the road under no load, when you accelerat it runs fine stars hard once and a while.
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Dpierce
April 1, 2009.



Ok there is no key on engine off specs but it should build up enough pressure to start. Yes the fuel pump will only run for about 3 seconds with the key on engine off but it should run all the time with engine running. With that the fuel pressure should be 60-66 psi and needs to have full pressure to start. With you problems I must ask how old is the fuel filter?

Racefan966
Apr 1, 2009.
New Fuel filter a week ago, new cap, rotor, wires, and spark plugs, I have 62 to 64 PSI with key on and when I start the motor the fuel pressure drops to 56 to 57 PSI and stays there at a idle

Tiny
Dpierce
Apr 1, 2009.
Ok the fuel pressure is low when it is running. So check the vacuum line going to the pressure regulator make sure it is good. If all that is good then unplug the pressure regulator and see what the pressure does. It really needs to be in that 60-66 psi range. Get back to me with what you find.

Racefan966
Apr 2, 2009.
Where is the pressure regulator on this 1996 Tahoe
with 5.7, is it in the plenum? It is not visiable to me and I don't see the Vaccum line either

Tiny
Dpierce
Apr 2, 2009.
Yes it is under the upper plenum and it doesn't have a vacuum line to it as it is set by spring pressure internally. So if the fuel pressure is low this is more then likely the problem. Also these injection systems like to crack the fuel lines that connect to the injector unit and leak. So I would replace the regulator and check those lines for any signs of leaking there is a repair kit for them at most parts stores if it does look like it cracked. With out the fuel pressure up to full pressure there isn't much more we can do for tests as this will affect them. Let me know what you do and how it goes.

Racefan966
Apr 3, 2009.
We replaced the fuel pressure regulator, it was washed out and clean right under the regulator like it had been leaking, flushed injection system, then had to clear the codes because of missfires, took truck out for a drive and it still acted up. Put scanner on it and it all looked good except for -14 on cam timing. Took it to my local GM dealer and they reset the timing and said the truck was fine, But now when I go up a hill under load it pings and knocks then goes away any ideas

Tiny
Dpierce
Apr 8, 2009.
Check the knock sensor make sure it is pluged in and working.

Racefan966
Apr 9, 2009.