Fuel pressure

Tiny
DPIERCE
  • MEMBER
  • 1996 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 220,000 MILES
1. What should the fuel pressure be when the key is turned on, motor not running?
2. What should 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 misfires show on hand held scanner, truck sputters going down the road under no load, when you accelerate it runs fine starts hard once and a while.
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Wednesday, April 1st, 2009 AT 10:05 AM

9 Replies

Tiny
RACEFAN966
  • EXPERT
Okay, 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 three 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?
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Wednesday, April 1st, 2009 AT 10:29 AM
Tiny
DPIERCE
  • MEMBER
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.
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-1
Wednesday, April 1st, 2009 AT 10:42 AM
Tiny
RACEFAN966
  • EXPERT
Okay, 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.
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Thursday, April 2nd, 2009 AT 10:34 AM
Tiny
DPIERCE
  • MEMBER
Where is the pressure regulator on this vehicle?
With 5.7, is it in the plenum? It is not visible to me and I do not see the vacuum line either.
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Thursday, April 2nd, 2009 AT 10:58 AM
Tiny
RACEFAN966
  • EXPERT
Yes, it is under the upper plenum and it does not 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 is not much more we can do for tests as this will affect them. Let me know what you do and how it goes.
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Friday, April 3rd, 2009 AT 9:49 AM
Tiny
DPIERCE
  • MEMBER
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 misfires, 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?
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Wednesday, April 8th, 2009 AT 1:39 PM
Tiny
RACEFAN966
  • EXPERT
Check the knock sensor. Make sure it is plugged in and working.
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Thursday, April 9th, 2009 AT 10:35 AM
Tiny
TYLERDEBUSK18
  • MEMBER
I just traded for a 1997 two door Yukon with a Vortex 5.7. It will not start unless you put a little gas in the breather. I tested pressure it is like at 40 psi when you turn key on fuel pump runs is it just not strong enough to start it?
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Monday, April 30th, 2018 AT 5:04 AM
Tiny
ASEMASTER6371
  • EXPERT
Dpierce.

The cam retard at -17 is not good. The dealer change the position of the distributor to get the 0 reading that the cam sensor requires.

Doing that s compensation for a worn timing chain. That is why you have pinging. Most likely you will need to replace a worn timing chain and then have the cam retard reset.

Roy
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Wednesday, May 2nd, 2018 AT 4:58 AM

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