I have a 98 Blazer throwing a code: DTC P1345 CKP (crankshaft) /CMP (camshaft)Correlation. The motor was replaced 30k miles ago and is a gm 4.3L long block installed by a dealership. The motor runs great. About the same time I started getting the code the tachometer began acting "choppy", jumpingup and down in200 or 300 rpm intervals, not smoothlyrunning up and down. Anyone have any ideas or experience with this problem? I would appreciate it. Due to the motor's youth I doubt I have a stretched timing chain. If the disctibutor was a tooth off it wouldn't run as good as it does, and the code would have been present since the motor was dropped in.

 

As the tach signal comes from the CMP sensor, it sounds like the CMP sensor (camshaft position sensor) is dropping signal for some reason or another. You should inspect the wiring, but I have a feeling that the CMP sensor is on its way out. If you have the distributor from the other motor, you could try swapping that in or just swapping the CMP sensor over. You may need a CASE relearn (also known as crankshaft variation learn procedure).

RE: Where is the cam positioning sencor? - shows how to remove the sensor.
P1345 Explained - explains the code you are experiencing and the diagnostic procedure accompanying it.

 

Thanks. Is there a way the CMP can be tested with a multimeter before I sink some coin into one? I'm guessing the CASE relearn is something I'll have to take it to the dealer for?

 

I am unaware of any functional tests that can be performed with a DMM on the CMP sensor, but I'll take a crack at it... Looking at the wiring diagram and knowing that it is an hall effect sensor, the BRN/WHT wire is the signal wire to the PCM, the PNK wire is the +12V power wire from the ENG 1 fuse, and the PNK/BLK wire is the 1x CMP signal wire to the PCM. The sensor should operate by either being open (no +12V power on the PNK/BLK wire)) when there is no metal between the gates and closed (+12V on the PNK/BLK wire) when there is metal between the gates, or reverse of that, open when metal is present and closed when not.

Unless you know someone that has a comparable scan tool to the Tech2 the dealer has, yes, a dealer or repair shop is required for a case relearn.