I'm going to drop this here hoping it helps someone. I scoured this site but didn't find a direct hit. I finally came across a "just answer" thread that described my issue exactly.
I don't know the exact sequence of events but here goes. 2005 Sierra Z71 4WD 5.3L crew cab.
The truck was dying randomly but would always fire back up. Sometimes I'd have to crank a lot, sometimes it was immediate. It finally quit working completely just sitting in my backyard where I had parked it to make room for people to park because I was hosting a party. Very unfortunate spot to die.
It really felt like a fuel issue, so I replaced the pump. It didn't fix it and introduced a new problem - fuel level was inaccurate. Side note: it's easy to get the float jammed up in the tank when installing the new pump. I removed and reinstalled the pump and the gauge worked. I verified that the pump was priming, and I had pressure at the rail.
Still won't run so I checked for spark. Ain't none. But why?
The article I stumbled across recommended a scan tool to:
The above assumes you've eliminated the security module as the problem (your SECURITY light isn't flashing or constant on) and you've verified 12V+ at the coil harness (pink wire).
The last step in the article was to ground one of the coils. The grounds for all 8 coils are on the same harness so grounding one grounds them all. I put a safety pin through one ground wire and used alligator clips to ground it. The truck fired right up!
So there's either a break in the ground wire or it's corroded where it's attached to the block. The ground in question is directly above the front axle "pumpkin" attached to the bottom of the block (driver's side). It's not easy to get at. I inspected the wire as well as I could and didn't see any break in it. I cut open the harness, found the wire and used a line tap to run a ground to the alternator bracket. That fixed it.
I'm pretty sure I had two separate issues. The old fuel pump was failing intermittently. Then the ground thing after I parked it.
I don't know the exact sequence of events but here goes. 2005 Sierra Z71 4WD 5.3L crew cab.
The truck was dying randomly but would always fire back up. Sometimes I'd have to crank a lot, sometimes it was immediate. It finally quit working completely just sitting in my backyard where I had parked it to make room for people to park because I was hosting a party. Very unfortunate spot to die.
It really felt like a fuel issue, so I replaced the pump. It didn't fix it and introduced a new problem - fuel level was inaccurate. Side note: it's easy to get the float jammed up in the tank when installing the new pump. I removed and reinstalled the pump and the gauge worked. I verified that the pump was priming, and I had pressure at the rail.
Still won't run so I checked for spark. Ain't none. But why?
The article I stumbled across recommended a scan tool to:
- Check cranking RPM. If none, the issue is probably the crankshaft sensor. I had cranking RPMs so I'm good there.
- Check spark advance while cranking. If none, then it's probably the camshaft position sensor. I had spark advance while cranking so that's not the issue.
The above assumes you've eliminated the security module as the problem (your SECURITY light isn't flashing or constant on) and you've verified 12V+ at the coil harness (pink wire).
The last step in the article was to ground one of the coils. The grounds for all 8 coils are on the same harness so grounding one grounds them all. I put a safety pin through one ground wire and used alligator clips to ground it. The truck fired right up!
So there's either a break in the ground wire or it's corroded where it's attached to the block. The ground in question is directly above the front axle "pumpkin" attached to the bottom of the block (driver's side). It's not easy to get at. I inspected the wire as well as I could and didn't see any break in it. I cut open the harness, found the wire and used a line tap to run a ground to the alternator bracket. That fixed it.
I'm pretty sure I had two separate issues. The old fuel pump was failing intermittently. Then the ground thing after I parked it.
