Whelp, This Was a New One For Me!

While Automotive field is no longer my primary field for bringing home the bacon so to speak, I am college trained Automotive & Heavy Duty Diesel Mechanic, with a concentrations in Electrical Diagnostics and I am known in my area for being a "problem solver" (I don't always solve them but it bugs me to know end if I don't get to finish/find the solution).  These days I do Diagnostics on the side on the weekends for hobby money...anyway...this one surprised me, and it's been quite a while since that's happened.

INFO:
Vehicle:  2007 Chevy Silverado Z-71, 5.3L L.S.
Issue:  long crank before start, throws CKP circuit code, CKP relearn code, sometimes runs rough, tachometer doesn't work (never has).
Customer Comments:  2nd owner, bought at auction in 2009 with "hard to start" had 45K on it...has owned it since 09, never solved the hard start, rough running issue, has put new sensor in, new pigtail on sensor end of harness, nothing ever fixed it.  Took it to have it detailed, detail guy hands him a paper says, found this while detailing - had original owners information on it.  set it in the truck, didn't think about it until it was acting up (running rough) one day and thought, hey maybe I can find out why the original owner got rid of it and why it went to auction.  Contacts original owner - he says, truck always did that from the day he got it., New sensor, new PCM, new harness, updated PCM programming etc. (all under warranty) nothing ever fixed it and they wouldn't approve a new motor (not sure why) under warranty, so finally they let him trade it in with a good discount towards new vehicle, and it (evidently went to auction).  Current owner says thanks for the info and just lived with it because otherwise it was a nice truck and wasn't his only vehicle.  well, due to other circumstances he has had to make it his daily and the issue is really annoying him now...so ends up bringing it to me.

Diagnostic process (after doing code scan):
1.  pull starter, pull CKP sensor, bench test sensor - test fine, but have a known good one on the shelf (I work on a lot of LS vehicles), put it in - confirm same issue.
2.  pull up Alldata, get wiring diagram.  isolate all wires from the rest of the vehicle modules and PCM connector and check for continuity - they are all good.
3.  load test each wire - can light a test light on each wire - load test good.
4.  reinstall wires into PCM connector and reinstall - check 5V ref circuit - good have 5V ref, check ground - good as well.  back probe into signal wire, reinstall sensor and harness, as well as starter.
5.  start vehicle (long crank time), no tachometer, no signal from the crank sensor when monitored from scantool and O-Scope...rack my brain and finally think, well if I eliminate all the wiring and PCM, what's left that would do this....reluctor wheel...maybe it's bent, not aligned on crank correctly...hmm...
6.  pull starter back off, pull CKP sensor out, stick snake camera in CKP sensor hole and jaw hits floor - NO RELUCTOR WHEEL FROM THE FACTORY...Really GM, REALLY?

So, tell owner, good news, I found the problem - bad news, going to cost what a motor swap does to fix it because motor has to come out, crank has to come out and either the correct reluctor wheel has to be pressed on or a replacement crank installed, etc.  Customer is surprised as to what the problem I found was and said he would schedule the repair...I told him, if that didn't fix it, bring it back to me and if for some reason I still can't get it to start and run right... I'll cover the labor for the repair.

Final outcome:  repair completed, truck runs and drives perfectly - another happy customer - other than he probably won't buy any more auction vehicles...LOL.

What an awesome story! I love it. Well done.

Wow! That's insane, nice find.

Great find! 

I had a similar issue last year. New-ish Ram 1500 got a reman engine for some reason. Afterwards, it had a long crank and P0339 that wouldn't go away.

CKP waveform was odd. Lots of missing pulses, but always at the same point in the crank rotation. Ruh roh. Borescope of the crank reluctor found several of the teeth were gouged and/or ground down:

drive.google.com/file/d/1j5vRwXnS-sfirFj...SKi/view?usp=sharing

Don't ask me how. Engine got dragged across the floor, maybe? Customer got the engine covered under warranty.