Hillbilly_Mailman

I recently replaced my 4.0 from my Cherokee with a lower mileage 4.0 from another. Both were a 96 and were nearly identical, except mine is a RHD (right hand drive). The new 4.0 is in and it turns over, has plenty of Battery power, but when I turn on the key, the power to the coil only lasts about 2 seconds. Even when I turn the engine it won't fire a 12v tester light but for that 2 seconds of initial startup. I am worried that the flywheel from the newer engine is the culprit and that the CPS isn't reading it right. Could there be two or more different designs from one Cherokee to another in the same year. I did replace the CPS with a new one as well as the coil just to be safe. Neither helped!! If anyone else has had this problem I would greatly appreciate some help.

Hillbilly_Mailman

I checked out the flywheel and it looks the same. I also changed the CPS modual on the tranny "again" and still no luck. Is there anything else that can stop the spark at start up at the beginning of the coil besides the CPS? Someone has gotta have the answer to that, right????

solderjunkie

Have you ever heard the other 4.0 run?

Usually the PCM will command the coil to spark based on the first sensor that lets the PCM know which cylinder is at TDC. If the engine tries to start and the crank sensor does not jive with the cam sensor, the PCM gets lost and stops commanding the coil.

Maybe someone has pulled the distributor/cam sensor and reinstalled it out-of-time.

jpdocdave

the cps is also very picky about how its put in. i'd like to know some more info, i'd like to know if anything else is missing, do you have injector pulse and fuel pressure? a lot of times there's more than just spark missing, and that can help with whats wrong.

is the cps in a different spot on the other motor due to the right and left hand drive?

Hillbilly_Mailman

I did have both 4.0's running before I changed them over. The CPS is located at the same spot on both the RHD and the LHD. I haven't checked the fuel pressure and injector pulse. I will have to give that a try. Thanks for helping and I will repost as soon as I find something out. I may just tow down to the mechanic in the morn and see what he can do.