Does the CKP sensor on a 1996 chevy blazer need a variation relearn

No, but it sounds like a fuel injector problem. Do you notice it run really rich? A pressure and leak down test will tell you if it is your problem.

I do not know but the exhaust has been smelling strong lately and these have weird poppet valve injectors. I just had that whole spider assembly under the intake replaced with an updated Delphi unit and a Delphi fuel pump installed. The whole problem started when the truck suddenly was hard to start, it cranked over like the timing was off. So I had a new distributor installed and that didn't fix the problem, and then it went on from there. I was told these blazers do not like any replacement parts but AC Delco and I thought that was just crazy that a vehicle could be that sensitive to replacement parts considering this is not a brand new vehicle. Then I was told it was the Bosch O2 sensors that were installed. Then it was the EGR valve, then the IAC valve. I wish I could nail this problem down.

Have the fuel pressure and leak down test done and go from there. All you need us a fuel pressure gauge. Your looking for 55psi and it shouldn't drop when the key is off

Is this a Federal or California build? It makes a big difference.

I got a 96 LS 4 door it was having the same problem and I found a vacuum leak pretty major one but I replace the vacuum hose and fix the problem it's running fine now vacuum leak I had was from the PCV valve to the little canister that's attached to the hood