Fuel pump no prime on key switch?

CRYSISFREAK7

MEMBER
2000 CHEVROLET SILVERADO
4.8L
V8
2WD
AUTOMATIC
268,000 MILES

I have check to make sure my fuel pump works by jumping pin 30 to pin 87 on the relay panel and the pump kicks on, I verified continuity on the pump ground wire at the pump plug to frame, I verified continuity from the grey wire at the pump plug to the engine bay gray wire and all is good, I have 12v at pin 30 but none at 86, 86 seems to be ground switching tested by measuring resistance which jumps up when ignition on, im getting no power to 85 when I switch the ignition on, orange wires coming off the back of the relay box for 85 and in stumped on where to check next, any help would be greatly appreciated. If it helps I changed my spark plugs and fuel filter right before this occurred, I don't believe I left anything unplugged as I didn't need to unplug anything for the filter and left nothing unplugged for the spark plugs, I did tear a coil wire for passenger front most plug and removed the wire and when I started the vehicle I heard it arcing to the metal frame holding the heater core lines and I shut it off and unplugged that ignition coil to be safe.

Friday, August 15th, 2025 AT 2:09 AM

5 Replies

KEN L

MASTER CERTIFIED MECHANIC
54,137 POSTS

So pin #86 is suppose to be ground. #85 get power from the PCM so I would start by checking the fuses for it, ENG1 IGN1 etc. Here is a guide to help, please check the fuses with the key on.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Can I ask if the security light is flashing? If so this is the problem, I would try a hard system reboot, here is a guide to help show you how.

https://www.2carpros.com/articles/step-by-step-guide-performing-a-hard-system-reboot-for-your-vehicles-electronics-systems

Please go over these guides and get back to us.

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Friday, August 15th, 2025 AT 5:39 PM

CRYSISFREAK7

MEMBER
3 POSTS

So I went over the electrical system in the truck and I found that there is good continuity for the green and white wire going to pin 9 for the pcm plug. I also verified that the ground pin was good and verified again that pin 30 had constant power and the relay pin going to the fuel pump gray wire was continuous to the fuel pump and all checked out so I believe I may be settled on a PCM failure because regardless of the good continuity in the harness from PCM pin 9 to the fuel pump relay slot it is still not delivering power when the key is turned on or the truck is trying to start. I went ahead and jumped the relay so I could get the truck home and I am now left with another question the truck now has a very hard shift from first to second and what feels like a double shift from second to Third could this possibly be also related to PCM failure. Again the only things I changed on this truck for basic maintenance was the fuel filter and the spark plugs and today I went ahead and put on new spark plug wires and reconnected the disconnected ignition coil and now out of nowhere I'm having a fuel pump not engaging and a very hard shift in the transmission. I checked all of the fuses and all of the fuses are fine and the security light only flashes when the key is out of the ignition when the key is put in the ignition and turned on there is no security light.

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Friday, August 15th, 2025 AT 5:44 PM

KEN L