89 MJ cranks no spark

[Marko]

I’ve been working on my Mj for a while now. Recently truck would not turn over after several attempts. Changed spark plugs, cap, rotor and coil. Truck started up!! Within a month or two same issue. Disconnected the cps for 5min, truck started right up. So I replaced the cps and engine cranked up but it started to misfire and die out. Now I’m unable to start it. No spark, cleaned out grounds, checked power source to coil 👍🏽, new cps 245ohms. Gas pressure 👍🏽. I need some insight to the problem.

[NSWelding]

Only time I had no spark on my 4.0 wranglers was a bad coil. No moisture in the cap? 

[Pete M]

On 5/5/2023 at 11:45 PM, Marko said:

I’ve been working on my Mj for a while now. Recently truck would not turn over after several attempts. Changed spark plugs, cap, rotor and coil. Truck started up!! Within a month or two same issue. Disconnected the cps for 5min, truck started right up. So I replaced the cps and engine cranked up but it started to misfire and die out. Now I’m unable to start it. No spark, cleaned out grounds, checked power source to coil 👍🏽, new cps 245ohms. Gas pressure 👍🏽. I need some insight to the problem.

 

have you accomplished Cruiser54's MJ tips yet?  most are electrical related.     link is one of the first in the link in my signature.

[cruiser54]

What Pete said^^.

Also, the resistance test on the CPS is inaccurate. You want AC millivolt output. 

Chances are your original CPS is a better one than the replacement. 

 

Tips 1, 3, 4 and 5 first and foremost. Here's how to check the CPS correctly and even increase its signal output. 

 

CRUISER'S MOSTLY RENIX TIPS

RENIX CPS TESTING AND ADJUSTING

OCTOBER 30, 2015 SALAD 131 COMMENTS EDIT

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 itself as shown in Figure 2 as Connector A, 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 the upper mounting hole to 3/8″ from the stock 5/16″, or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.

Another little tip to save tons of aggravation is to stick a bit of electrical tape to your 11mm socket and then shove the bolt in after it. This reduces the chances of dropping that special bolt into the bell housing.