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Pressure Leak???


jthomp23777
05-16-2009, 10:54 AM
2001 Tahoe,130,000. Having starting hesitation problem on start up. Does not fire as quickly as used to.Fuel pump is original. I did a fuel pressure test. I get 58 psi on ignition turn on,55 psi when running.The pressure test gauge will not maintain pressure on just turning the key in the on position, it leaks down quite quickly.Should'nt the fuel pump maintain pressure on the fuel system with the key just in the ON position?The gauge maintains pressure hovering at 55 when the engine is running.All other coponents are well maintain,plugs at 88,000,fuel filter every 10,000,throttle body cleaned regularly,battery holding load and at 14 volt,starter appears to be turning engine over other than it engages longer due to this start up problem. I guess my question is with the pressure test gauge leaking down quickly is this normal or not?? Thanks

j cAT
05-16-2009, 11:24 AM
2001 Tahoe,130,000. Having starting hesitation problem on start up. Does not fire as quickly as used to.Fuel pump is original. I did a fuel pressure test. I get 58 psi on ignition turn on,55 psi when running.The pressure test gauge will not maintain pressure on just turning the key in the on position, it leaks down quite quickly.Should'nt the fuel pump maintain pressure on the fuel system with the key just in the ON position?The gauge maintains pressure hovering at 55 when the engine is running.All other coponents are well maintain,plugs at 88,000,fuel filter every 10,000,throttle body cleaned regularly,battery holding load and at 14 volt,starter appears to be turning engine over other than it engages longer due to this start up problem. I guess my question is with the pressure test gauge leaking down quickly is this normal or not?? Thanks

the fuel pressure must hold for 15 min at the pressure when the engine is running within a few psi...if it rapidly drops this is usually a bad fuel pump....

check the fuel regulator for fuel in the vac line going to it...the injectors ,,,may be leaking down but if that where the case with the drop off very rapid I would think this would cause engine issues/dtc..

when you start,, turn key to ignition ,,,wait two seconds engage starter..

the 55psi is on the low side,,,but your gauge may be off a little..
when you install a new pump only use the DELPHI PUMP...THEN measure the fuel pressure and test for holding of pressure....you may also for insurance replace the fuel pump relay as well...

jthomp23777
05-17-2009, 06:54 AM
Thank's j-cAT,always appreciate your input to the members of this forum as well as the regular contributers. The fuel pressure gauge holds steady at 55 psi with the engine running.I only get quick leak down of the gauge with the key just in the ON position(engine not running).The pressure shoots up to 58 psi and instanly starts dropping back to "0".I would think that that fuel pump would maintain the pressure on the gauge.The regulator vacuum line is dry,already rule that out.I just return from a 3000 mile trip and no problems other than the slow start up. It used to crank up on a dime. I do have a new AC Delco pump with the upgraded wiring harness.I just don't want to put it in yet until I know it is a pump issue. The engine runs smooth,no hesitation when driving, accelerates well. I am just wondering if I am not getting adequate fuel line pressure on start up and system is leaking down too quickly as determine by the fuel pressure gauge and this is causing the slow start up.If one of the fuel injectors where leaking down. How would you find it? Is there a way to test each injector. On another note would a leaky injector send a code to the computer. Thanks for the help...

J-Ri
05-17-2009, 12:38 PM
I have seen many of these, when they do what yours is doing it's almost always the pump. You can block off the return line and see if the pressure still drops, that would rule out the regulator leaking to the return line. I'm pretty sure there are no rubber hoses on that, so to block it off you'll need to get a quick connector of the right size and cap that and install it on the fuel rail. Or depending on what adapters you have for your gauge, you can install it on the return side of the fuel rail, that's what I do but my tester was expensive and has every adapter imaginable. I'm not too sure what all comes in the DIY price range sets. DO NOT pinch the hard plastic lines shut, you'll damage it. To check if an injector is leaking, cycle the key on and let the pump prime a few dozen times. If it starts and runs normally after that, and blocking the return line doesn't help, then it is 100% without a doubt the fuel pump.

You already checked for gas driping to the ground, right? :)

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