89 Cherokee Troubles: Intermittent No Start

1989 Cherokee, 4.0L, auto. I have been chasing my tail with intermittent no start issues on my daily driver. Things started about 3 weeks ago. While driving, the Jeep will suddenly stall out on the road...completely shut down, then after about 5 or 10 minutes it will start again. I've also had it not fire up on a cold start a couple of times. I've been going through some of the usual issues. The CPS was replaced about a year ago, resistance reads 234 ohms. The ignition switch was replaced recently. The coil and ignition module are about a year old. TPS is adjusted correctly. Both the grounds from the body to the head and on the oil dipstick tube have been throughly cleaned. The B+ latch relay is good and functioning. Fuel pump was replaced about 1 1/2 years ago and holds good pressure at the rail. While troubleshooting the issue I've found that when the Jeep is stalled out there is no spark. I've checked & verified that the ignition module is getting 12 volts, is there a way to check for a signal from the ECU? What other things should I be looking into?

Thanks,
justin

you won't be able to check for signal without the DRB tool or an o scope. Did you check the CPS while it was no starting? Have you unplugged the CPS, shorted all the pins to ground and then replugged and tried to start?

Sounds like the CPS. It should be between 175 ohms and 225 ohms with a meter from one wire to the next IIRC.

I replaced mine when I did a tranny swap one time and then it started to hickup when warm stalling at odd times. Turned out the wire had touched the manifold and would ground out as it got hot.

Also they do demagnatize over time too, in that case they have to just be replaced.

Try checking voltage output from the CPS for giggles. It needs to be at least 350 AC millivolts or you will have starting/stalling issues.

The spec on the Renix CPS/CKP crank sensor is 200 ohms, + - 75 ohms, or 125~275 ohms.

If you have confirmed no spark then it is the crank sensor, the ECU, the ICM, or the coil, the B Latch relay, or the harness in between.

As you have 12 volts to the ICM the B Latch relay is eliminated.

Clean and put a little dielectric grease on the ICM/coil clips.

As said, you need a DRB scanner or a Snap-On 2500 with the correct adapter to check for the ECU signal to the ICM.

Make sure the mounting bolts for the crank sensor are tight, as well as the rest of the bellhousing bolts--the crank sensor functions off of an air gap.

I'll look into the CPS a little more when I get off work today, will let you guys know what I find.

Thanks,
justin

Had a chance to crawl underneath the hood of the beast after work today. While attempting to crank I found that the volts coming out of the CPS were at 0.3. If I understand correctly they are suppose to be within 0.5 & 0.8? If that's true, then it would point to the culprit. As stated earlier, the CPS has been replaced about a year ago...probably got about 10,000 miles on it, bought the thing from NAPA. What kind of lifespan should I be looking to get out of these things?

Thanks,
Justin

Just replaced the one on my 1989 after 200K miles.

There are two different signals generated by the crank sensor depending on the notches passing it.

Pull the 3-wire connector at the ICM, measure resistance between A and B; 200 + - 75 ohms is what you are looking for.