Hello everyone I have an 89 xj 4.0 that i just completed a motor swap in. after its first start it ran fine for a couple of minutes and.. like an idiot.. i pulled the battery out of it while it was running to replace it with its original. ( I've worked on more chevrolets and this is acceptable with them) So it died, then it would not start up, after days of toiling with it i came to find out that when i did that it blew the crank sensor, so i replaced it, now it will start, and it sounds like complete crap. It backfires,and it sounds like the timing is off horribly but ive checked it with a timing light multiple times and it is fine. Also I have swapped two different distributors into it thinking this may fix the problem.. but no. If anyone knows what may be the problem or has any ideas for me or for stuff to check, that would be great! thanks

 

is the ground goin to the CPS in good shape?

 

What does it do when its cold? What does it do when its at operating temp.? Does it do it when you bring the RPM's up? You have fuel right, hahaha sorry had to ask.

Try that ground for the CPS, and then make sure your fuel pump is working good. Worst case is that you may have fried your ECU. The juice from the battery could have back fed to your ECU.

 

That is may also be another reason but check your ground first. Grounds can screw you over bad.

 

I havent checked that ground but i will, thanks.. and it doesnt matter what temperature it is, it does the same thing no matter what. Its so bad that i cant drive it or anything..

 

yea i have good fuel pressure, yea i think i may have fried my ECU also, but i dont really wanna go spend $120 on a new one and then it not be the problem.. is there any way to check to see if my ECU is working?

 

go get one from a junkyard.

 

check them good,My jeep was a no start for 4 years and the PO had replaced everything.I found a broke ground wire,fixed it,fired right up.

 

To my knowledge there is no way to check the ECU. It would be a JY part, but even then you never know. Bummer. But it sounds like your ECU since your fuel pump is good and timing is right. Hopefully not but its going to be an expensive lesson if so.