I have a 1986 cherokee 4 cylinder 2.5 with a mind of its own. When it stops running there is no high voltage from the coil although there is always 12-13 volts throughout the ignition. I have replaced the coil, ignition control module, distributor cap and rotor. After replacing these parts and checking, there is still no high voltage or spark to the plugs until the engine suddenly decides to start. It will run for a while then die, again with no spark to the plugs. I have had to tow it home twice. There is four wires going to the ICM, one is 12 volts, one is a ground, I think one goes to an ECU, which I think is somewhere near the flywheel and the other I'm not sure of. Whats killing the high voltage from the coil ??

 

Just as a guess, I would check the crankshaft position sensor. It could also be a fault in the ECM/PCM.

 

[QUOTE=Giovanni;1463136]I have a 1986 cherokee 4 cylinder 2.5 with a mind of its own. When it stops running there is no high voltage from the coil although there is always 12-13 volts throughout the ignition. I have replaced the coil, ignition control module, distributor cap and rotor. After replacing these parts and checking, there is still no high voltage or spark to the plugs until the engine suddenly decides to start. It will run for a while then die, again with no spark to the plugs. I have had to tow it home twice. There is four wires going to the ICM, one is 12 volts, one is a ground, I think one goes to an ECU, which I think is somewhere near the flywheel and the other I'm not sure of. Whats killing the high voltage from the coil ??

Thanks for the reply Firestorm. I have a Haynes repair manual and it only lists a PCM and an ECM on later models. Do you happen to know if these devices are on my model and where they are ? Also, do you know if I can readily access the crankshaft position sensor and is it capable of killing the high votage ?

 

After doing some research I believe the ECU is under the dash and may be the problem. Anyones thoughts on this ? Also does anyone know if the TDC sensor mounted near the flywheel is capable of killing the high voltage from the coil etc.

 

I believe your CPS should be near the flywheel, probably on top of the transmission bell housing.

If your '85 is like my '87, there is a computer box located under the glovebox area, attached to the lower dash panel.

 

Check the CPS absolutely first. Nevermind ECUs and the like just yet.

If you have a manual trans, the whole problem could be that worn off clutch material has stuck to the CPS since it is magnetic. That fouls up the signal to the ECU.

 

Thanks for the replys. Since a new ECU is so expensive I'll probably try and get a used one somewhere. I suspect this is the problem thinking of all the symptoms. I imagine it must be from the exact vehicle, eg year, engine, transmission etc. Can anyone confirm this and also I saw a guy on e-bay who rebuilds them ???

 

Thanks for the reply Cruiser. I don't think my 86 4cyl 2.5 has a CPS according to Haynes. It does indicate a TDC sensor somewhere near the flywheel. These acronyms are driving me crazy !

 

That's a CPS in another form. It has one. Do what you think you gotta do..........