What is causing my Yukon to intermittently not start?

Tiny
RON1MOONEY
  • MEMBER
  • 1999 GMC YUKON
  • 190,000 MILES
1999 GMC Yukon 5.7 2WD intermittently will not start. After a few hours of sitting it starts again like nothing was wrong. It may perform fine for days, weeks, and months and then fail again only to work again after sitting for hours with no worked performed. The engine turns over just fine but is not getting fuel. In the beginning I changed the fuel pump (three times). But as I changed the fuel pump each time it checked out fine. I have checked all the fuses and they are good. I have changed and checked the fuel pump relay and it is good. Using a wiring diagram I have seen the next component to check that controls the fuel pump is the Vehicle Control Module (VCM). The way I read the wiring diagram I should be able to apply 12V to the 87A socket on the relay board and start the fuel pump prime, is that correct? Am I on the right track? I see literally thousands of post about this issue with 90 model GMCs but have not seen a satisfactory solution.
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Monday, June 11th, 2012 AT 2:04 AM

15 Replies

Tiny
ASEMASTER6371
  • EXPERT
Did you change the connector at the fuel pump module?

Roy
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Monday, June 11th, 2012 AT 2:06 AM
Tiny
RON1MOONEY
  • MEMBER
Yes I changed it when I changed the fuel pumps.
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Monday, June 11th, 2012 AT 2:15 AM
Tiny
RON1MOONEY
  • MEMBER
Can I get another answer please?
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Monday, June 11th, 2012 AT 11:37 AM
Tiny
WRENCHTECH
  • EXPERT
How do you know that you're not getting sufficient fuel. What is the fuel pressure reading when this happens?
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Monday, June 11th, 2012 AT 1:34 PM
Tiny
RON1MOONEY
  • MEMBER
The car will not start and the fuel pump primer is not coming on. I can normally hear the fuel pump primer come on when I turn the ignition key to the on position but now it is silent.
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Monday, June 11th, 2012 AT 3:15 PM
Tiny
WRENCHTECH
  • EXPERT
That's what I thought. You need to use a fuel pressure gauge.
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Monday, June 11th, 2012 AT 3:22 PM
Tiny
RON1MOONEY
  • MEMBER
Not sure I am following you, the car will not start, therefore there is not fuel pressure, the guage will reflect 0, will it not? I need to know what is stopping the electrical current from getting to the fuel pump. I can apply 12v straight to the pump and it turns, the fuel pump relay is good, what stops the signal to the fuel pump relay?
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Monday, June 11th, 2012 AT 3:59 PM
Tiny
WRENCHTECH
  • EXPERT
You don't know that you don't have any fuel pressure. You haven't checked it.
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Monday, June 11th, 2012 AT 4:02 PM
Tiny
RON1MOONEY
  • MEMBER
For conversation sake, let's say the fuel pressure is 66 lbs at 1200 rpm. What could be telling the fuel pump relay to not engage the primer when the ignition key is turned on? Are there sensors that feed a signal to the VCM or is it a bad VCM?
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Monday, June 11th, 2012 AT 4:11 PM
Tiny
WRENCHTECH
  • EXPERT
I'm sorry, I don't work that way. I'll let someone else deal with this if they choose to.
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Monday, June 11th, 2012 AT 4:44 PM
Tiny
RON1MOONEY
  • MEMBER
The fuel pump relay is not engaging at the turn of the key. There is no audible click and the fuel pump itself doesn't come on. When I test the fuel pump relay it works fine, I replace it with a new one and it still doesn't engage. I simply want to know what component of the vehicle sends the signal to the fuel pump relay to engage the fuel pump primer when the ignition is turned on to start the car?
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Monday, June 11th, 2012 AT 5:15 PM
Tiny
RON1MOONEY
  • MEMBER
I paid money for an answer and all I got was more questions. Fuel pressure is not necessary to tell me which component sends the signal to the fuel pump relay. That is equilivant to me asking how to change my flat tire and being told to check the air pressure in the tire. MY RESPONSE: Well their isn't any air pressure the tire is flat. EXPERT'S REPLY: You don't know that there isn't any air pressure you haven't checked it. MY RESPONSE: But the tire is flat and the rim is touching the ground. EXPERT'S REPLY: That's what I thought you need an air pressure gauge. MY RESPONSE: Because there is no air in the tire and it is completely collapsed, let's assume the tire is actually flat how do I change it. EXPERT'S REPLY: I'm sorry I don't work that way. If the expert would have just read what I was asking it wasn't for a diagnosis, it was for the name of the component that controls the fuel pump relay. The answer to that question would not change regardless of what the fuel pressure was or is. I will be requesting a refund of my donation.
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Wednesday, June 13th, 2012 AT 11:47 AM
Tiny
WRENCHTECH
  • EXPERT
http://i1198.photobucket.com/albums/aa448/Wrenchtech/78553822.gif
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Wednesday, June 13th, 2012 AT 12:36 PM
Tiny
RON1MOONEY
  • MEMBER
Thank you. So as I read this schematic, the dark green/white wire, at pin 85, coming from the VCM should send an electric signal to the fuel pump relay for 5 seconds when the ignition key is turned on, which sends a signal to pin 87A activating the fuel pump primer connector, then that current stops, the relay flips the other way, activating pin 30 and the current from the orange wire coming from the Underhood fuse block passes through the fuel pump relay to energize the pump during normal operation of the engine. And pin 86 is to a ground. Is that how you see it?
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Wednesday, June 13th, 2012 AT 1:04 PM
Tiny
WRENCHTECH
  • EXPERT
I will be having no further involvement in this question.
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Wednesday, June 13th, 2012 AT 1:30 PM

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