Missfires

hello all
This is the first time I have post so bear with me please.
I have a 1988 cherokee Pioneer, auto,4.0
It seems to missfire badly When I get to cruising speed.If I give it the gas it clears up. As soon as I resume cruise speed it starts missfiring again. I may be wrong but I think its when the trans shifts into drive. If I drop into 3rd it straghtens up. the Engine is freshly rebuilt.I have replaced the tps,o2 sensor,coil,ICM,cps.
This is getting exspensive. I sure could use some input.


91 XJ 4.0 STICK STOCK
88 xJ 4.0 AUTO STOCK:

Did you use new injectors?

Did you use a new fuel filter?

Was the distributor "indexed" correctly when the rebuilt engine was installed?

Thanks for the reply to my post Eagle.
The answer is no to all.I did check the resistance value for the injecters and it was good. I just installed the old dist. with new cap, wires, and rotor.I will have to find out how to index it. I know I saw a thread somewhere on how to do it.Would the filter or fuel pump cause it to faulter at a steady speed only?
By the way where do you live in CT. I was born and raised in Meriden.


Thanks again.

Mine stutters/stumbles at almost exactly 2000 RPM (a little after converter lock up) accelerating lightly. I´ve been periodically playing with the problem, haven´t found a cure yet. Too many other things have gone wrong and have sidetracked me.
I seem to have an excessive amount of play in my distributor shaft. The gears seem to be too loose and the rotor will move up and down an amazing amount. I have a used (some tighter) distributor that I´m gonna try soon. I re-indexed my distributor, which seemed to help some ( along with a new set of Champion plugs), but was kinda hard to do, by the book, because of the play. I ran the motor with the cam position sensor unplugged (accidentally), really smoothed out my idle (another possibility). I believe I have a intake leak, among other things, that may be contributing. Might be more than one problem, going on in my motor.
I checked out the fuel system on mine, fairly intensively, pressures on a three day test were all OK.
Problem seemed to be worst at low vacume, throttle half open.
A little tip, when cutting the locking tabs for the distributor. You can trim and notch an keep most of one tab. If re-indexing doesn´t help, finding your way back to the original position is much easier with most of one tab, still intact. Anyway be sure and mark the distributor base and block with a chisel, to keep track of the original position. Re-indexing the distributor, did richen the mixture a bit on mine, mostly at idle.
One thing I never did figure out, is when finding TDC are the timing marks, to be lined up, at the last notch, on the right or the next to last notch. Mine isn´t marked "0", and I went by the picture at All Data.com , which showed one notch before the end. Another oddity was timing chain play, I made sure my last turn was to the right. Turning back to the left caused a lot of diference in the position of the rotor tip.
Hope I´ve helped and not confused

Well Eagle got it right again.
I went back and indexed the distributer.I modified an old cap so that I had a window too view the rotor and found that it was pointing dead center on the electrode of the cap.Eagle said it should be just leaving the electrode.I have to admit that I was not convinced that this small amount of adj. would make that much diff. but it did. I ended up taking the Jeep to a auto repair shop that I knew was competent to see if they could solve my problem.They spent 3 days working on it and were stumped. They finaly came up with a TBS that
Chrysler came out with in 1988 (TSB No.18-53-88 July 1988). It said to modify the dist. just as eagle had described.They called the TBS 4.0 Eng. ignition cross fire-modify distributor.Anyway thanks to those who helped.This is a great forum.
Richdoo

Does this re-indexing only apply to '88 or all renix up to '90 ?Also does this only need to be done when removing distributor type deal.Just curious if they put out a TSB in '88 wouldnt they have addressed the problem in the following years ?maybe Im thinking to logical.

MACH90XJ said:

Does this re-indexing only apply to '88 or all renix up to '90 ?Also does this only need to be done when removing distributor type deal.Just curious if they put out a TSB in '88 wouldnt they have addressed the problem in the following years ?maybe Im thinking to logical.

Click to expand...

Sorry MACH90XJ but I dont Know the answer.
The TSB was for 1987-1988. You would think that the problem would have been resolved once they knew about it, but I dont know. Maybe someone else
on the forum can answer that.Eagle may know.