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no spark

rydizzy

NAXJA Forum User
I have an 89 Cherokee 4.0 that wouldn't start yesterday morning. I looked at it after work last night and found no spark. Looked a little deeper today and found a couple things. The distributor points and the rotor are fried, a couple plug wires are rusted at the ends, and inside the distributor it looks green like an old penny. Just for fun, I checked power to the ICM and the resistance of the coil. The ICM is getting 12v and has a good ground. It is also receiving the 5v pulse from the ECM. The coil resistance between the positive and negative posts is 11.1 ohms. Is that high enough to cause a no spark condition? When I looked up what the resistance was supposed to be, it said close to 0 ohms..but how close is close?
 
11 ohms is probably right. Where did you test for spark, before or after the cap and rotor? Where did you ground it to test for the spark? try testing the coil tip to ground.

Have you replaced the coil and cap and rotor?
Oh, and open up the ICM/Coil, and clean the clips and pins inside, they get loose and nasty on the input side of the HV coil!!!!
 
I checked for spark after the distributor originally, then from the coil after I saw the condition of the cap and rotor. I tried grounding in several places(even the negative terminal). I already cleaned the contacts between the coil and ICM and squeezed the clips closer together. When I check the coil tip with a voltmeter, I pick up voltage, but it will not spark. Tried with several plugs/wires from working vehicles. I even pick up voltage after the distributor, but it is a bit lower and sometimes goes away.
 
I know you said the ICM is getting a 5V on off signal, but have your tested the CPS yet?

Usually no spark is a bad or weak CPS. Otherwise maybe the ICM is bad? Or the ICM firing ground, ground is bad? I think the ICM grounds the low voltage side of the HV coil to fire the coil?

87-90 is notorious for bad sensor and control ground issues.

http://www.naxja.org/forum/showthread.php?t=1072534
 
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
 
I had another Renix that had cps problems and someone was talking about the tach movement while cranking. On that Jeep it didn't move until after I fixed the cps problem. On this one it does move, so I was just assuming that it's fine. I probably should've checked it anyway. It'll have to wait until tomorrow now.
 
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I checked the cps. It is barely reading at all. .02v When it is plugged in, the tach moves and when it's unplugged, the tach doesn't move. So it's obviously getting a signal. maybe my volt meter is incorrect.
 
vI'm part polish..set the voltmeter to d.c. battery voltage instead of a.c. Switched it and it reads .45 volts with a weak battery. I'm going to pick up an ICM/coil at pick n pull and see if it works.
 
Have you tried this?

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
 
See post number 3, he already did that. Nice write up in though.
 
Stole it?:eek:

I will send you a bill, LOL!:clap:

But I am flattered, LOL.
 
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