Help with Cherokee Ignition(ECM Problem)

[Jason01]

I have an 88 Cherokee, and Im having a problem with the Ignition. I have pretty much traced it to the computer. The jeep runs fine on an idle once it starts, but, as soon as you touch the gas, it begins to misfire. I have traced the problem to the Ignition output on the computer. The waveform on my labscope kinda falls off and becomes extremely erratic. Right now, im guessing that the ECM is a lil dead, but the problem has been getting progessivly worse, but all of the inputs in the the ECM appear to be good and normal. has anybody had this problem before? If you have PLEASE help me from going nuts! I forgot to put that it has the 4.0.

edited by: Jason01, Mar 17, 2003 - 09:39 PM[addsig]

[MudderChuck]

About the only tried and proven advice I can give you is, that a long time ago, I made up my mind, that I was going to check the basic mechanical functioning of my motor (87 XJ 4 ltr.) before I spent the money for some "expert" to go on a fishing expedition with a diagnostic tester (he doesn´t understand anyway) for $40-$50 an hour. And 90%+ of the problems were in basic areas.
Bad distributor cap, corroded connectors, plugged or fouled sensors, vacumn leaks, high voltage cables or just plain moisture, inside the ignition system somewhere.
That said, the early XJ´s had a series of coil failures, a recall type thing, that might require a look.
And Dingus at sometime or the other, posted the base values for the crank position sensor, that should affect timing. In later models the pickup in the distributor (trigger) seemed prone to failure.
One problem, while simple drove me nuts, water under the mounting plate inside the distributor. Only misfired when the motor was warm and some of the water would evaporate and cause some serious misfire. The distributor cap, also seemed prone to corrosion, and would carbon track and fire the wrong cylinders at the wrong time, the higher the RPM the worse the problem.[addsig]

	Crank position sensor A crank sensor is a component used in an internal combustion engine to monitor the position or rotational speed of the crankshaft. This information is used by engine management systems to control ignition system timing and other engine parameters. Before electronic crank sensors were available, the distributor would have to be manually adjusted to a timing mark on the engine.

[MudDawg]

If the ignition is a Autolite sourced unit, you could rig in a "blue grommet" ford ignition module as a test...But unless you have mechanical and vacuum advance, it isn't a permanent solution...but it could help pinpoint the problem....oh yeah...have you checked to make sure the distributor bushings are OK?? it would take a LOT of slop, but it could cause the kind of problem you are seeing....[addsig]

[bluebelle]

is sounds like the misfire is from ignition and as we know, misfires often come from timing.

have you checked your timing? may have a stretched chain - how many miles on her?

mudder's right on the money - almost always engine problems lay in the basic stuff. rarely do electronics go bad before the mechanicals.
[addsig]

[LIVEWIREME]

HEY JASON01 I JUST BOUGHT A 87 XJ 4.0L I6 WITH AUTOMATIC TRANS IT IS DOING THE SAME EXACT THING. I WILL LET YOU KNOW WHAT I FIND. IF YOU FIND SOME THING PLEASE LET ME KNOW. THANKS LIVEWIREME@SBCGLOBAL.NET[addsig]