Todd Higgins

Got a 89 jeep cherokee with a 4.0L. got no spark from coil. coil resistance checks ok. any one know how to check the module. coil bolts to module. got power and ground. not shur on signal from pick up coil yet. don`t have vehicle here. a wire diagram would be greatly appreciated as well. thank you.

tjwalker

I don't think you can test the ignition control module without specialized equipment. Call around to parts stores to see if they can help you with that.

But before that, I'd test the "crankshaft position sensor". It is likely the #1 cause of no spark on the Jeep 4.0 engine. Here is the how-to.
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Renix (87-90) Crankshaft Position Sensor 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 crank sensor directly from the Jeep dealer for best reliability and longevity.

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.

Todd Higgins

That is some very knowledgeable and sound advise. Forgot to mention that i advised customer of cps and he changed it. he got a cheapy and installed himself. not a mechanic buy any means. Think i`ll go with you and my gut and past experience and start over. Thanks for the testing methods. Makes alot of sense. Just been stoppin bye here and there to get it figured out. Thank Yall. Happy Holidays!

cruiser54

This, too:

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

Todd Higgins

Thanks Renix, Good advise as well. I looked at contacts and they look alittle shady. When i can get back to jeep i will definitely check on all your suggestions. I`ve worked for G.M. for 23 years and at home for as many. Jeeps just always seem to elude me. Love the drive train and suspension problems though. Easy money. LOL. Ever need help on a G.M. product, holler! P.S. You stay up awe full late. LOL

tjwalker

Cruiser54 never sleeps. Never.

The Rooster

here is a wiring diagram for you for the Renix jeeps
https://www.cherokeeforum.com/f23/te...itings-136452/
and yea cruiser never sleeps.. pssh hes on the west coast lol

cruiser54

I just get up early , like 4 am on Mountain standard time.

Todd Higgins

Hey guys and gals. Finally got back to this jeep. aftermarket crank sensor sending out .38v ac to .42v ac. have power and ground to module. unsure of how to correctly test cam sensor. every diagram i try to pull up just doesn`t seem to match. This is all stock stuff. Cleaned coil to module contacts and measured coil primary and secondary resistance, good. on module to coil from connector goin into module i only show a good connection on positive leg. I`m aware that the negative is toggled by the pcm through the module. All terminals clean and tight. What is the refferance from pcm to module? positive or negative toggle? If someone can help me with the correct wiring diagram would be of great help. I`m aware that that this aftermarket crank sensor isn`t up to par and really needs oem. Old school thinkin, i should be able to fire the coil through the module as long as i have power and ground, then toggle the the refferance wire to module, but i don`t know if it`s a ground or positive. Don`t wanna fry it if it ain`t already. Thank Yall, Been a great help so far!
Todd Higgins.
P.S. Incase all pertanant info didn`t stay with thread. 1990 jeep cherokee, 4.0L manual drive, 4wd. Renix ignition, coil on module assem.

cruiser54

Doesn't have a cam sensor. The sensor in the dizzy is for sequential injector firing only.

You can increase the output of your CPS just in case there's enough resistance in the circuit to make it's .38 to .42 AC volts not reach the ECU.

TurtleFD

Check the resistor on the side of the engine compartment.
White looking block about 2-3 inches long.
Those going out on older jeeps = no spark
I might have one still if you're in the denver area.

cruiser54

That resistor is NOT for spark. It's to reduce fuel pump noise.

Radi

The Signal from the pcm to the ignition module is a 5 volt square wave. The leading edge of the square wave causes the module to ground the coil, the trailing edge causes the module to open the primary and fire the spark.


This drawing match?:

Todd Higgins

Thanks to all! awesome pics, info, and directions. Feel pretty confident that with all the correct info I`ll have this thing properly diaged today. Anyone needin G.M. help, holler. 23 yrs exp. in them. Experience and the correct info, priceless! Let yall know what i come up with.
P.S. cruiser, sounds like you know these jeeps better than the back of your hand. LOL.
G.M. and Jeep seem to both had their wiring issues in the 80`s and 90`s. Probably had their harnesses made by the same company. LOL

Todd Higgins

I wanna thank yall! been great help. turned out to be the module. all the grounds and positives were corroded and needed cleanin. Surprised it had any power anywhere. After all the cleaning and adjusting the cpm as cruiser suggested. my cmp cam up to .42 - .51. still had no spark. checked referrance from pcm to module, still good 5V. tried old school thinkin to fire coil and nothin. so, went with module seein that all inputs were good and still nothin. Fired rite up. again, Thanks a bunch!!!!
Todd Higgins
P.S. on the engine to body ground, i moved engine ground to the next head bolt up just to be easier on me. Also, cleanin connections, a die grinder with a cookie as i call it, is much quicker than sandining.