Hey guys, my buddies 2000 Wj 4.0 has this weird misfire. To start it started with the replacement engine he had put in, since the first start theres no spark in cylinder 6. So we checked the plugs and swapped the coil and nothing then we went to the dealer and got a new Cam and crank sensor still nothing. We checked the grounds and took the ECM and key module out of my WJ just to see by any chance its the Ecm does the same thing... Im stumped... Any opinions would be appreciated.

 

Free bump because I am curious.

 

check to see if power is going to the coil first and work your way back from there.

 

Cylinders #1 and #6 fire simultaneously on the same coil and you changed that. Check plug #6 for a cracked insulator. I got a Champ like that right out of the box! Are you sure it's not a bad injector? Is the injector plug cracked? Was the injector harness damaged in the swap? The injectors are controlled by drivers in the PCM. Make sure you don't have a bent pin in the PCM harness plug.

The injectors are supplied with a constant 12 volts and are grounded thru drivers in the PCM to control fuel. There is a cool tool called a "Noid" light that will show if the injector is firing or not. You might try someplace like Autozone to rent one.

 

Yes we did use a noid and the injector is firing. Gonna have to double the the harness and the pins. Im wondering if its possible that the flex plate has anything to do with it. Im sure he used the flex plate that came with the used replacement engine, maybe it could of been bent or have a different number of teeth and messing with the crank sensor. Im gonna give him a hand on this again tomorrow after work Ill keep you guys updated. Thank you

 

Let us know what you find out.

 

It's entirely possible the CPS got damaged in the swap. I've talked to transmission shops and they tell me they replace the CPS with every trans change just to be sure.

 

OK update, problem solved! We checked everything we could think of to no avail. So we pulled the motor back out to remove all the wiring and start checking everything one thing at a time...again but when we got the motor out and put it to the side I realized the flexplate had a slight bend in it right at one of the holes where the crank sensor sits
(I tried taking pictures but couldn't really see it in the pic) So we straightened it out got the engine back in and now it runs beautiful! I think the weight of the engine rested on the flexplate for a moment during install. So be careful and take your time. Hope this helps someone.

 

Thanks for coming back to let us know and glad you figured it out!!

 

The flexplates are thick metal. Seems like it would be pretty tough to bend one. Interesting problem and fix though. Nice work.