Hello everyone. I have a head scratcher for you

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Bandit

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I have a 1995 GMC YUKON 5.7 that is taking me for a loop. I just rebuilt the top half of the motor. anything touched was replaced with new parts. no cheapy. ac delco only.
Here is the problem at hand.
Wife driving to work monday morning and the truck was fine at the red light. Light turned green and she went to go and the truck died. no restart. I showed up to save the day and there is no fuel pump humming. <ie> bad fuel pump. I ordered in a NEW ac delco fuel pump. reading some of the forums, Google alot. come to find out the GROUND at the FUEL pump RELAY is INOP> no ground! ok jumped relay bang the pump starts! yay....NOPE tried to start no fire! it wont fire up! I am stressed and now I need YOUR help. I am all ears on what to do and where to look.
Please and Thank you for all information in fixing this truck. If I cant fix the truck I might be having a BON FIRE WITH IT!!!! and its the kindling!
Thanks,
Jack
 

SunlitComet

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So with pump running it will not restart correct? you had to bypass the relay to get the pump to run? Have you tested for a spark.
?
 
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Bandit

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i jumped the pump and STILL no fire up. pump will only run if bypassed.
 

Haro504

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Have you checked the wiring diagram? maybe what ever powers the pump also powers other ignition components.
 

SunlitComet

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bandit, don't have my primary computer up right now. give me about 24hrs to get it up and review the tech data for a clearer answer. but iirc the fuel circuit is initially run by a ecm controlled relay after which an oil pressure switch takes over the job. that being said if you run it manually for say one minute and disconnect the jumper something is wrong with the oil pump pressure switch, fuse or such.

looks something like this wiring diagram on this page. http://www.2carpros.com/questions/chevrolet-tahoe-1995-chevy-tahoe-car-starts-then-dies
 
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Bossy70

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Well, it seems that you are losing power to your fuel pump and spark plugs... your ignition switch or lock cylinder could be the problem. It is their job to send power to your starter, fuel pump relay, and ignition system when you turn the key into the "start" position.

Check for spark at the plugs.
 

retorq

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Just because the pump is pumping doesn't mean it's pushing the pressure or amt the engine needs, verify that.
 
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Bandit

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ok update. came home after work (now) turn the key on the on position nothing. went to the right side head to grab a hold of the ground wires and before actually grabbing them <ie> (as hand was entering between firewall and head) the fuel pump kicked on. waited for it to cycle. got off the bumper and went inside truck and it started!!!!! unknown what was touch moved or rubbed currently to fix or diagnose the issue. waiting for the am to be able to see as well as hopefully less mosquito's still up for advise. it anit over till this fat yukon pig sings!!!!
 

SunlitComet

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there are "master grounds" that mount from battery and frame rail that mount in the back of engine. generally on the right cylinder head.
 

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