Alright fellow gear heads. Did a recent build on the 4.0l comp cam lifters, head work, msd ignition, Bosch 4hole injectors, and fresh ckps. Jeep is hard to start but idles fine until 1700 rpm then it starts to stumble. Timing is jumping all over the place when you put the light on it. We're stumped. All sensors have been checked and or changed. Timing is set properly as well....verified but multiple shops. Suggestions? New ECM as well.....well reman..
I haven't gotten too much into the distributor, but that's where I would start looking for problems. Loose drive gear maybe? I don't know if it has mechanical advance weights like a v8 does, but perhaps a problem there?
My cylinder head overhaul: http://www.jeepforum.com/forum/f13/cylinder-head-r-r-picture-heavy-1348138/
My transmission overhaul: http://www.jeepforum.com/forum/f13/how-change-transmission-electronics-1560948/
I had the stock cam and lifters in and it did the same thing. Thought I might have gotten a bad set of lifters. Dropped their high energy cam for fuel injected 4.0l in it and their lifters. Same thing still...
Haven't gauged the vacuum but its strong it'll die out if you smoother it. Cat is a manga flow. Fairly new., I did reconnect but might try cleaning them again. I did run a ground straight from the battery to the engine with no improvement.
Bump. Come on guys.....where are the techs at? I've pinned out all the grounds and signal wires and have found no problems.....checked the tone ring and its fine as well.....just before taking it to the dealership.
My only thought is that your crankcase position sensor (CKPS) is too far away from the flywheel (it wasn't properly seated during installation). If a CKPS is positioned too far away from the flywheel, it will cause problems at higher RPMs. What are the symptoms? I'm not sure because I've never personally encountered this problem. I've just read that a CKPS that is too far from the flywheel will cause timing issues (including backfires and misfires) at higher RPMs.
So, perhaps you should remove it, put on a new spacer (or check to ensure the old spacer is still good), and reinstall.