This Suburban came in today mil on and running poorly with a complaint of no power.I scoped the CKP signal and could not make a decesion based on what was seen in the scope capture so I decided to graph the fequency of the CKP signal and sure enough I caught a glitch and pulled the trigger on the CKP but upon the test drive it felt better at first but after some real power was required it acted the same way again and you can hear a little engine noise.

I did not save the first round of waveforms so back to the shop to have another look heres the CKP waveform under snap throttle conditions and it was easily produced at higher rpms in the bay and I was carefull not to hit the rev limiter function of the PCM.

[2000 Chevrolet Suburban K1500, ECM/Inputs/Outputs waveform]

and here are the some snap throttle conditions only graphing the frequency

[2000 Chevrolet Suburban K1500, ECM/Inputs/Outputs waveform]

I had seen in the archives that there had been some issues with crankshaft endplay possibly causing this so I had a look.

Beginning measurement

[2000 Chevrolet Suburban K1500, Engine/Propulsion photo]

Ending measurement

[2000 Chevrolet Suburban K1500, Engine/Propulsion photo]

These measurements where taken from the back of the flexplate through the inspection hole using a prybar at the balancer.There was also a fairly recent looking oil leak coming from the rear main area and the spec for crankshaft enplay according to mitchell is .002-.008 and we measured .066 . So the sensor itself was not bad but the crankshaft movemnet is causing the signal to flake out and I found the graphing function of my meter to a good job of showing where the root cause is.

I hope this can help someone

Tperk

Thomas from Missouri

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