Serious misfire problem with 4.3 csfi.

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CKP variation relearn allows PCM to recognize crank reluctor wheel teeth properly. It does not change cam retard value. I've been hiding under the doghouse of V8 vans for so long now that I can't remember whether or not OE 4.3 distributors can be turned. I know that OE V8 parts can. There are a couple of aftermarket brand replacements which come with their own hold down which prevents the CMP sensor (distributor) from being adjusted. The fastest "fix" for those clamps is to put them in a vice and use a hammer to open the clamp up slightly. Presto chango adjustable dizzy.

FWIW if this had been titled "false misfire" or something similar the recommendations would have followed a somewhat different track. But I would still establish a baseline as previously mentioned. Misfire codes occurring when the engine seems to run fine can be extremely hard to track down and you want to make sure you know the mechanical parts are right before diving into pcm and related wiring.