original problem was 3.7volts on 5 volt wires and no spark,was drove to work and never cranked again, changed TPS, cold air sensor, clock spring, TCM, still 3.7v on old PCM. I changed PCM from another cherokee that runs great and same exact jeep but now I have no communication with this one. Any ideas?

 

What code is it giving you? If you still have the old PCM, put it back and start over. The PCM gets angry when grounds go bad, so check them. Remove and clean until shiny. Doublecheck the battery, its connections, and the cables themselves for signs of corrosion as sometimes thats all it takes, a bad connection. Shoot for atleast 12.6v with the engine off. Too low and the PCM gets angry again. Very fussy.

Here are a couple pics from CCken.