Oxen__

so when on a long drive like 60 mph freeway or around 30 miles my 89 xj 5-speed runs great. you get to about 40 mins and it starts missing , engine will cut out, tach will go dead when this happens. if i let it cool for a bit it will drive fine. its not over heating , radio lights heater all work fine when this is going on too.

i have good fuel pressure, i installed a new ground wire zero gauge , cleaned the ones on the engine , the one to the fire wall. no improvement.


is there a ICM on my jeep?

seem like engine bay heat is the issue. i can run on a trail all day no hiccups at all. i searched :89 xj cutting out, 89 xj missing and tach cutting out, 89 xj missing on freeway. found apost about grounds so i did them figured it couldn't hurt thanks for any help

DFlintstone

I guess the CPS has been known to crap out hot. The tack going makes sense since it monitors rpm, (I think). The test can be done in just a few minutes. I think it's freedgr who has mentioned a few times it's probably a good idea to do tests WHILE the thing is fouling up. A bit tough here, but maybe carry your meter and pull over when it starts missing! Here's two C/O Cruiser:


Renix CPS Testing and Adjusting
　
　
Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected.
You should get a reading of .5 AC volts.
If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out it’s mounting holes with the first drill bit that just won’t fit through the original holes. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.
　
Revised 11-29-2011



Renix Jeep ICU/Coil contact refreshing
　
　
The contacts between the coil and the ICU on your Renix Jeep can become corroded and loose causing a complete or intermittent no-start condition. I recommend the following procedure as a maintenance precaution to insure this is eliminated as a possible cause now and in the future.
The coil is attached to the ICU by two T20 Torx bolts. Remove these two bolts and lift the coil up off the ICU. You will see 2 pins and 2 sets of contacts. Clean both the pins and springy contact pieces with a good electronics cleaner.
Squeeze the springy contacts closer together with some needlenose pliers. Apply some dielectric grease to the contacts and bolt the coil back on to the ICU.
While you’re right there unplug the connectors from the ICU and inspect the pins in the harness connector. Make sure the pins are not retracted into the connector. Spray out the connector and the receptacle of the ICU with the same good electronics cleaner you used earlier. Apply dielectric grease to the connectors and plug them back in.
I feel this procedure should be performed at least once in the lifetime of a Renix Jeep.
　
Revised 11-29-2011

cruiser54

Great starting point Flintstone. OP, take his advice.

huntingman2706217

Coils are also known for failing once warmed up and xj's...

tjwalker

Excellent advice above. Crank sensor is my first suspect, coil and ignition control module next.

Oxen__

cps was clean checked good. i grounds were all good every thing was fine.

what was wrong : the pins that supply power and ground to the coil. there not in a weather tight connection lame right. they were dirty and a little corroded . also they were not tightly fitting to the pins , so the connection was very poor.

remedy: scotch bright pad , cleaned pins on coil, and the tabs that it fit into , took a small standard screw driver and bent the tabs in a bit to tighten the connection.

Problem solved !

if your rig is acting alike a cps even tho it tests good. remove the coil like i did. its just two torx screws and out it comes. took longer to diagnose than the fix did.

happy motoring

cruiser54

That's why I wrote this. Everyone with a Renix should do this along with a good and proper ground refreshing at least once. Thanks for posting back!!

Renix Jeep ICU/Coil contact refreshing
　
　
The contacts between the coil and the ICU on your Renix Jeep can become corroded and loose causing a complete or intermittent no-start condition. I recommend the following procedure as a maintenance precaution to insure this is eliminated as a possible cause now and in the future.
The coil is attached to the ICU by two T20 Torx bolts. Remove these two bolts and lift the coil up off the ICU. You will see 2 pins and 2 sets of contacts. Clean both the pins and springy contact pieces with a good electronics cleaner.
Squeeze the springy contacts closer together with some needlenose pliers. Apply some dielectric grease to the contacts and bolt the coil back on to the ICU.
While you’re right there unplug the connectors from the ICU and inspect the pins in the harness connector. Make sure the pins are not retracted into the connector. Spray out the connector and the receptacle of the ICU with the same good electronics cleaner you used earlier. Apply dielectric grease to the connectors and plug them back in.
I feel this procedure should be performed at least once in the lifetime of a Renix Jeep.
　
Revised 11-29-2011

Oxen__

i did refresh my grounds. like i stated originally.

none the less still i good write up.

i ended up reading thru electrical diagrams and noticed the coil doesn't have a actual connector only contacts. so i went there and bam found what i was lookin for.

oh yeah i also skimmed thru your write up before i even bought a Xj i'm sure thats ware my cleaning the grounds and adding another one came from.