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99 Suburban Starts...Won't Run

Ok...this has been a reoccuring problem for little over a year now. It first happened in July 2002, again in June of this year and yet again this past weekend.

In all instances the Suburban was driven over 100 miles the day before and then allowed to sit outside overnight. In the morning the Suburban starts instantly, but then cuts-out and dies immediately after start-up.

This start-up then die sequence will happen for almost exactly two hours before the truck will finally start and run fine.

I have replaced the oil pressure switch as someone has suggested recently. As the key is turned you can hear the fuel pump run and see oil pressure guage move. But, just after the engine starts it dies...it does not stall as if from a plugged fuel filter, injector, etc.

Is there any computer input, sensor or signal that would shut down an engine right after it has started? It seems to me that a sensor has become damp from either weather or condensation and the signal from this sensor is required to allow the engine to run once started. The engine starts instantly and strong...there is no hesitation on the start...it just doesn't want to run.

When the truck finally runs, it starts and runs perfectly for months on end. Like I said it tends to do this after a long trip where the truck then sits overnight outdoors.

Any thoughts? Would the Helm shop manual be a good place to start diagnosing this type of problem?

Thanks!

Mike S. Kalamazoo, MI

Reply to
Mike Schudel
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Forgot to mention this is a K1500 with the 5.7L gas engine. Vehicle has approximately 95K miles.

Mike S. Kalamazoo, MI

Reply to
Mike Schudel

Reply to
David J and Lynne J Shepherd

Same thing I was thinking... Turn the key on and it primes for a few seconds, start it and the pump should run full bore till you turn the Sub off. I would do the relay swap first. You also might wanna check the box on the steering column that is run by the ignition switch via a rod. When the key is released from the start position it might cut out enough to turn off the fuel pump.

Reply to
Shades

Although we tried jumpering the fuel relay to directly connect the fuel pump, the same problem occured. I will still replace the fuel relay and may even change the fuel pump. I even thought in the back of my mind that it could be the ignition switch too.

We even tried holding the key in the start position and let the truck crank for about 30 seconds. Here it would start normal, instantly die and while the starter was cranking, every once in a while it would momentarily catch for 1/2 second...but not enough to start the engine.

Thanks for the suggestions guys!

Mike S. Kalamazoo, MI

Reply to
Mike Schudel

. . . . =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

It sounds like it runs on the initial prime relay pressure then when the ecu takes over the pump quits. Try to get a test lite on the power wire to the fuel pump and see if there is current to the pump during the event. Of course this will be tough if it is this intermittent. Or just replace the fuel pump relay and see what happens.

=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Re: 99 Suburban Starts...Won't Run Group: alt.autos.4x4.chevy-trucks Date: Mon, Oct 27, 2003, 7:42pm (CST-2) From: snipped-for-privacy@yahoo.com (Mike=A0Schudel)

Although we tried jumpering the fuel relay to directly connect the fuel pump, the same problem occured. I will still replace the fuel relay and may even change the fuel pump. I even thought in the back of my mind that it could be the ignition switch too.

We even tried holding the key in the start position and let the truck crank for about 30 seconds. Here it would start normal, instantly die and while the starter was cranking, every once in a while it would momentarily catch for 1/2 second...but not enough to start the engine. Thanks for the suggestions guys! Mike S. Kalamazoo, MI =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

check yer ignition module first.

marsh monster ~:~

Reply to
Marsh Monster

Your truck has a Passlock system. If someone was to pull the lock cylinder out of the steering column and try to start the truck with a screwdriver, this is the action the computer will perform, momentary start and just allow you to keep cranking. Is your security light on in the instrument panel? It still could be a bad fuel pump, you need to get a pressure guage on the system.

Reply to
WBucha

Fuel pressure regulator? Steve C

Reply to
Steve Cook

Have you hooked up a fuel pressure gauge? What is you pressure? Steve C

Reply to
Steve Cook

No. When this happens (so far three times in over a year) it NEVER happens at home. :-( Once at a family reunion, once while camping and once at our relatives cottage. After two hours of trying to start the truck, it starts and runs perfectly for about 6 months on average. So, needless to say, when I get home it is running fine. Besides, we would have to haul all the test equipment everywhere we went to test it under these non-running conditions and then we only have a two hour window in which to narrow down the problem.

I am leaning towards ignition module, ignition switch or passlock system just because of the way the engine shuts down after start-up. I know how an engine acts with plugged fuel filters, injectors or bad fuel pump or relay. It just doesn't act like any of these. I am convinced it is an electrical problem...but just can't diagnose it fast enough.

Mike S. Kalamazoo, MI

Reply to
Mike Schudel

Here is something I found that sounds EXACTLY what the problem is...

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Under GM Anti-Theft System Usage - System Name and Properties "Passlock".

"The Passlock system disables the injectors 1-2 seconds after startup. It has no effect on the start circuit."

I think this is it...I have a faulty controller or module associated with the Passlock system.

Mike S. Kalamzoo, MI

Reply to
Mike Schudel

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