Hey All,

I hope someone can help me with this problem.

I have a 1996 Grand Cherokee 4.0L 4x4.

It currently is getting no or momentary voltage to the coil while in the run position. I have plenty of voltage in the start position though (this info is base on a test light connected to the green/orange coil wire).

I have checked all of my wiring and can find not problems with the wire. Also I have replaced and moved relays around to eliminate the ASD as the culprit.

Any help you can provide would be greatly appreciated.

Doc

 

Crankshaft position sensor is a primary suspect. They are a VERY common failure on the Jeep 4.0 engine.

 

I've already replaced that 3 times twice with a after market and the last one is a genuine Mopar CPS. A Jeep dealer also put in 2 computers. I've also replaced just about every sensor under the hood.
What happens is that you put the ignition switch into the run position and the test light lights for a couple of seconds then goes out. When you crank the engine the test light stays on the whole time.
It actually reminds me of the old balast resistors how the engine would start until you let the switch return to the run position.
Thank you,
Doc

 

Spark: 12 volts from ignition switch to the ASD relay; when the key is first turned on the PCM provides a ground to the ASD relay to energize it, then the ASD relay passes 12 volts to the coil primary side. If no crank sensor signal is generated after a couple of seconds the PCM cuts the ground to the ASD relay (and fuel pump relay too) and that cuts power to the coil (and fuel pump). Key to START and once again the PCM energizes the ASD relay. Now, a critical element is the crank sensor--no signal from the crank sensor and the PCM won't trigger the coil to provide spark.

 

Ok but how can I keep going through CPS's? or could it be the connector/wiring coming from the PCM?

 

Almost assuredly not your crank sensor, unless there is a problem with the crank sensor connector or wiring (gotta look at the entire circuit).

Other suspects would be the ignition switch or the computer.

 

Just checked the voltage coming from the PCM and it was 5.15v well within specks according to my Haynes manual. I'll have to find the thread with the ohm readouts again to check the CPS. I checked it before I put it in and it was within specs. Unlike the aftermarket one I replaced.
Once again thank you for your help.
Doc