I recently bought a used 1999 2WD Tahoe 5.7L for my son, so I don't know the history. When I bought it, it had a starter problem - excessive grinding, but it would eventually start. Now it won't start and I think I've diagnosed it to the VCM but since they so rarely fail, I'm looking for suggestions. Here's the flow of events:
1. Replaced the starter. Worked fine for a couple of weeks. Then it started grinding.
2. Replaced the starter again. Swapped the direct drive version for a gear reduction version.
3. Vehicle started fine over the course of 3 hours in the driveway. Roughly 30 starts - cold and warm start conditions.
4. The first attempt at starting the next morning produced excessive grinding noise and the vehicle would not start.
5. Found GM Service Bulletin 00-06-04-014 basically stating a bad crankshaft position sensor can advance the timing up to 50 degrees and cause excessive grinding among other things so I replaced the CKP.
6. Due to frustration between steps 1 and 2, I had already ordered new battery cables to rule them out. It wouldn't hurt to change the 18yr old cables anyway. So those were swapped.
7. Replaced the starter relay. It was working but the plastic housing could be easily pulled off.
8. Installed another gear reduction starter (my buddy at the parts store was kind enough to warranty it).
9. The Tahoe now cranks with no noise but doesn't start - no spark from the coil.
10. I swapped the CKP again just to be sure. No change so I started real diagnostic procedures.
11. 12v coming to the pink wire on the CKP.
12. Purple ground wire of the CKP is good.
13. Yellow signal wire of the CKP only registers 8v AC during cranking - my information says this should be at least 10v AC. If the wire is good all the way to the VCM, it says replace the VCM.
14. Checked continuity between the yellow signal wire and the yellow wire on pin 31 on the blue VCM connector - all good.
15. Checked the ignition control module and verified it is not getting an Ignition Control (IC) pulse signal to the white wire. Stays hot but does not flash an LED test light. This indicates its not getting the VCM pulse which implies a bad CKP, VCM or the wiring in between, right?
16. At first DTC codes were P0336 and P0339. I cleared them and now just getting P0336.
It seems pretty clear this is a VCM problem but there are no visible signs of corrosion and they go bad so rarely. The VCM is on order. Did I forget something? Would shimming the CKP increase the AC voltage on the signal wire or decrease it?
1. Replaced the starter. Worked fine for a couple of weeks. Then it started grinding.
2. Replaced the starter again. Swapped the direct drive version for a gear reduction version.
3. Vehicle started fine over the course of 3 hours in the driveway. Roughly 30 starts - cold and warm start conditions.
4. The first attempt at starting the next morning produced excessive grinding noise and the vehicle would not start.
5. Found GM Service Bulletin 00-06-04-014 basically stating a bad crankshaft position sensor can advance the timing up to 50 degrees and cause excessive grinding among other things so I replaced the CKP.
6. Due to frustration between steps 1 and 2, I had already ordered new battery cables to rule them out. It wouldn't hurt to change the 18yr old cables anyway. So those were swapped.
7. Replaced the starter relay. It was working but the plastic housing could be easily pulled off.
8. Installed another gear reduction starter (my buddy at the parts store was kind enough to warranty it).
9. The Tahoe now cranks with no noise but doesn't start - no spark from the coil.
10. I swapped the CKP again just to be sure. No change so I started real diagnostic procedures.
11. 12v coming to the pink wire on the CKP.
12. Purple ground wire of the CKP is good.
13. Yellow signal wire of the CKP only registers 8v AC during cranking - my information says this should be at least 10v AC. If the wire is good all the way to the VCM, it says replace the VCM.
14. Checked continuity between the yellow signal wire and the yellow wire on pin 31 on the blue VCM connector - all good.
15. Checked the ignition control module and verified it is not getting an Ignition Control (IC) pulse signal to the white wire. Stays hot but does not flash an LED test light. This indicates its not getting the VCM pulse which implies a bad CKP, VCM or the wiring in between, right?
16. At first DTC codes were P0336 and P0339. I cleared them and now just getting P0336.
It seems pretty clear this is a VCM problem but there are no visible signs of corrosion and they go bad so rarely. The VCM is on order. Did I forget something? Would shimming the CKP increase the AC voltage on the signal wire or decrease it?
