1999 suburban

I'm having problems with my daughters 1999 Suburban, it wont start. I replaced the relay and the fuse is good, dropped the fuel tank and removed the fuel pump then checked the wires and got no juice. I also tested the fule pump by running a hot wire to the terminals and it works. Is there anything else between the relay and the pump that would go out so as not to get power or am I on a bad wire hunt?? If so is there any common areas to look for the bad spot??

I don't know on a 99 but on a 97 the fuel pump only runs for 2-3 seconds when you turn the key to "ON" (not start). At this point if the pump and filter are good, you should have 60 lbs. plus or minus 10% at the test port on the fuel rail on the left side of the engine. When you try to start it the ECM pulses the fuel pump and after the engine oil pressure gets to 4 Lbs. there is a bypass switch that switches +12V around the fuel pump relay and this is what powers the fuel pump. You proved the pump would run by applying +12V to it, but not that it can deliver the correct pressure at the fuel rail. Have your daughter help you and put your ear by the fuel tank door and have her turn the key and you should hear the pump run for about 3 seconds. I think you're on the right trail and I hope this helps. :)

This out of a '98 2nd edition C/K manual. When you turn the ign sw to "run" the VCM energizes the fuel pump relay for 2 secs and you should hear the pump run for that time. Everything comes from the VCM. It pulls in the relay which closes the contacts to supply power to the pump from the ECM B 20a fuse under the hood. You said the fuse is good but replace it anyway if the pump won't run for the 2 sec's. For the pump to continue to run it needs an input from the CKP (crankshaft position sensor) either cranking or running. The backup to the CKP is the oil pressure sender, which as Dave said, needs to be above 4psi and this would cause long cranking times before startup.

If it does run for that 2-3 sec's then you need to what "Dave" says and check fuel pressure at the rail.

Post back and let us try and help you some more.........Steve

Thanks guys, the 2-3 seconds was good to know, it helped. I changed the fuel pump relay and the pump and all seemed ok until today. The new fuel pump was leaking at the top of the tank because the rubber O ring pushed down into the tank instead of sealing. So we had to drop the tank and reinstall the new pump. When we dropped the tank we tried to start the truck to see if we could see the leak (not knowing it was the O ring at this point), and the truck would not start and we appeared to still have the same problem. Where do I go from here??
Thanks for the other advise it was very helpful.
By the way what is the VCM?
Bill

Some customers may comment on one or more of the following conditions:
• Backfire during crank/start
• "Kickback" during crank/start
• "No" start
• "Slow" or "hard" start/crank
• "Grinding" or unusual noises during crank/start
• Cracked or broken engine block at the starter boss
• Broken starter drive housing
• Broken starter ring gear on flywheel
• Any combination of the above
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=699690&pubid=96#ss2-699690">Cause

A condition may exist that allows the crankshaft position sensor to command up to 50 extra degrees of spark advance during engine cranking only. This in turn exposes the engine to higher than normal cylinder pressures which may result in an inoperative condition to the starter drive housing, the engine flywheel starter ring gear, or the engine block at the outside edge of the starter boss.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=699690&pubid=96#ss3-699690">Correction

Inspect for a stored powertrain DTC code P0338. This DTC will NOT illuminate the "Service Engine Soon" light. If this code is stored, the Crankshaft Position Sensor, P/N 10456607, MUST be replaced and the remaining components inspected for damage (engine block at the starter boss, the starter drive housing, and the engine flywheel starter ring gear).
Notice: When DTC code P0338 is set, failure to replace the Crankshaft Position Sensor could result in repeated inoperative conditions of the starter or flywheel.
Important: Some flywheel wear is normal; broken or missing teeth and/or cracks, are not normal.

<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=699690&pubid=96#ss4-699690">Parts Information

You need 53psi or more to start. Running pressure is 51psi.
Possible corrodded wiring under fuse block under the hood.
Follow the wire harness along the frame and watch for any green coming out
of the black conduit.

By the way what is the VCM?

Bill: the VCM is the Vehicle Control Module or the "computer".

ECM=Engine Control Module
PCM=Powertrain Control Module

They all do pretty much the same thing but are called different things depending on the year, model and motor(which you haven't mentioned yet?).

By the way what is the VCM?

Bill: the VCM is the Vehicle Control Module or the "computer".

ECM=Engine Control Module
PCM=Powertrain Control Module

They all do pretty much the same thing but are called different things depending on the year, model and motor(which you haven't mentioned yet?).


They gave it a new name when they incorperated the trans and eng pcm together. VCM Now just a new modern name :grinyes:
MT

You need 53psi or more to start. Running pressure is 51psi.
Possible corrodded wiring under fuse block under the hood.
Follow the wire harness along the frame and watch for any green coming out
of the black conduit.

Gmtechnician
Better recheck them specs.
4.8 -5.3- 6.0 -7.4 engins are 55/62 fuel pressure specs
4.3- 5.0- 5.7 engines is 60/66 fuel pressure specs.
MT
Guide lines on hard to start cold and checking fiuel pressure
Hard to start cold.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
4.8 and 5.3 and 6.0 is 55/62 lbs of pressure.
The 4.3- 5.3 -6.0 -7.4 are 60/66 lbs of fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.
MT