Reading about crank position sensors I learned that any time a sensor is removed and replaced the learn procedure is supposed to be done to return the system to proper function. The chevy manual I have says you need the code reader thing to start the learn procedure. Is there a way to do it without this expensive device or a dealers help?

I had to put on a new timing chain and now it acts sorta starnge. Once it refused to idle. On a test drive I felt a jump like it lost timing or backfired. I have also replaced the distributor with lost its bearing or sleeve and allowed the rotor to wooble so bad it distroied itself.

 

CASE relearn or Crankshaft Variation Learn is the name for the procedure. You'll need to find someone with the appropriate, bi-directional scan tool that can initiate the procedure whenever the CKP, CMP, distributor drive gear, distributor itself, cam, or timing set is replaced.

 

Can you purchase a decent bi directional scan tool? Is that thing harbor freight has in their advertisements junk for will it work to initiate the learn procedure after replace a timing set?

 

Actually, you may not have a problem with the Crankshaft Variation value, but rather with the CMP Retard which I recently learned about.

You still need a scantool capable of displaying CMP Retard which needs to be set to 0 degrees. This is accomplished by loosening up the distributor hold down bolt and rotating the distributor until the CMP retard hits 0.

As far as scantools go, I love my AutoEnginuity scantool. It shows CMP Retard as well as can initiate the Crankshaft Variation learn procedure.

 

The 4.3 engine distributor in 2002 does not rotate. When it is placed in the engine it fits into a locked position and even without the bolt in you may not rotate it. New ways are hard to fathom but that is how it was built.

 

That is what I thought not too long ago as well. According to the GM FSM, the cmp retard is modified by moving the distributor within the bore that it fits through in the LIM. The bore is a clearance bore that is oversized by a good margin to allow for ~15 degrees of modification in total.