Fuel pump will not prime

Tiny
LHEUREUX82
  • MEMBER
  • 2006 CHEVROLET SILVERADO
  • 6.0L
  • V8
  • 2WD
  • AUTOMATIC
  • 155,000 MILES
Hi everyone. I have the truck listed above SS. It’s a 2wd lq9 6.0 with 4l60e. While I was in the process of trying to find a tapping issue with the engine the truck stopped starting. It started and ran fine one day then the next it wouldn’t start. The truck cranks over great. I noticed the fuel pump wasn’t priming. Also the fuel gauge is reading empty like it’s not even working and the fuel light it on. Tank is half full of fuel though.

Things I’ve done so far are:
Took off the bed and checked to make sure the fuel pump works with my power probe. Fuel pump turns on when you give it 12 volts. Checked the plug and pins but they seem good. I replaced the fuel pump relay with one from the fuse box with something I know is working but that didn’t fix it. I tested power at the relay. The 30 pin has 12 volts when the key is on. Pin 87 has nothing. The thing I find weird is pin 86 the ground pin has only 10 volts when I check it for a ground. If I jump pin 30 and 87 the fuel pump with work all the time. I’m guessing I have a ground issue but I have no clue where to look. Don’t know where the 86 pin gets ground. There is nothing going to that pin from the bottom of the fuse box. I checked all the fuses I can find and have swapped all the relays with each other. I have cleaned the ground from the fuel cap to the frame. Also the ground on the engine block. Can anyone help me? I’m so lost at this point.
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Thursday, October 10th, 2019 AT 2:37 PM

3 Replies

Tiny
SCGRANTURISMO
  • EXPERT
Hello,

Pin 86 is the switched power supply to the coil, or the control side of the relay. The other end of the coil is attached to Pin 85, which is run to a ground. I would check the ground for Pin 85, which is Ground 104 for unwanted resistance and if that checks out then I would simply replace the relay. In the diagrams down below I have included the fuel pump wiring diagram, location and diagram of ground 104 and a general diagram of a 4 Pin relay, and a guide on how to check a ground. Please go through these guides and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros
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Friday, October 11th, 2019 AT 1:38 AM
Tiny
LHEUREUX82
  • MEMBER
Thank you for the pictures! These really helped. I had been trying to find where that ground was. Found the issue. The ground 104 at the transmission broke off. I installed a new end and put it back on the stud at the transmission. Turned the key and the fuel pump primed up. Truck now starts right up. Thank you for the great info!
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Wednesday, October 16th, 2019 AT 4:23 PM
Tiny
STEVE W.
  • EXPERT
Great to hear you found the problem. It's amazing the issues that can be caused by a missing ground. Thank you for using 2CarPros. Please return anytime with your automotive questions.
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Sunday, October 20th, 2019 AT 12:11 AM

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