b4ctrooper

Been messing with this thing and wanted a new opinion since I get stupid on my own stuff. Bought a 2003 2500HD non runner. I get no injector pulse with a noid light (test light on with the positive wire, 1 flash on the noid light then nothing), and I get no spark. When I turn the ignition to run, the starter also spins the engine which I thought was really strange. When cranking the engine on my HP Tuners scanner it shows 0 RPM. I repaired 3 broken wires in the harness. Still no good. Tested the wires at the sensor as per the FSM, all test good now. Replaced the crank sensor. Same results.

I deleted VATS with HP tuners. Still no start. 0 RPM cranking.

Back to crank sensor testing. I test the wiring again, and the B+ that comes from the PCM read 11.4 volts. Battery voltage was 12.5 volts. It is supposed to be the same as battery voltage. Tested the crank sensor reference Voltage at the PCM 11.4 volts. My 5 volt reference wires for other sensors read 4.8 volts at the PCM. I then tested the Camshaft sensor reference voltage at the PCM and also got 11.4 volts.

I tested the b+ wire into the PCM and the switched B+ wire, 12.5 volts each.

This is where I am right now. Any suggestions on where I should go from here? Are the 11.4 Volt readings enough to get a crank signal, or is that a strong possibility to be my issue? If so, would the PCM be bad then? I do have a spare PCM from a 2003 Avalanche I could try, but it was a 5.3L truck. Don't know if it would start.

mrvedit

Every silicon diode or transistor in a circuit drops the voltage by at least 0.2V; so your 11.4V should be fine.
HPT showing 0 RPM cranking does seem to indicate a bad crank sensor, bad crank sensor wiring or even a bad ECM. With no RPM signal the ECM will neither fire the injectors nor the spark coils; so no surprise there.
The starter spinning when ignition is in RUN, definitely needs to be fixed before proceeding; very likely a bad ignition switch, but checking wiring for a short.

b4ctrooper

After using an oscilloscope on it I had an erratic crank signal. Wound up pulling it back apart, cleaning the rusty block where the sensor mounts, and now I have spark and pulse. Drove me nuts for days!

mrvedit

Thanks for posting an update and solution.
Correct me if I'm wrong, but it sounds like you are saying the sensor also needs a clean ground connection through the mounting bolt?

b4ctrooper

If I get a solution, I always try to post it. Hopefully it helps someone in the future.

As far as the ground, the sensor is not grounded through itself, it grounds via the PCM. I think the problem was the sensor was not totally flush against the block and wasn't reading the reluctor ring consistently. I would have never been able to figure it out without the oscilloscope. One FSM test has you measure AC voltage from the sensor to see if it works which it passes. The problem is with one dead spot in the signal, that test gives a false pass.