have a 90 xj laredo 4.0 281,000+ miles and have been all over the many different threads already posted about this problem of my xj. how it will just crank and crank and nuthin. i replaced the ignition coil nothin, checked the cps and it seemed fine. so i checked out the distributor and the metal tabs on the rotor were broken so i got a new rotor and still nothing. just randomly i swapped the old coil back in and it started right up. i noticed i somehow cracked a vacuum line and so i was plugging it up (until i could get a new hose)and the car died. total time running was maybe a minute. cant get it to start again. theres about 12V coming off the ignition coil which i believe is correct. so heres the questions. if the cps was bad would there be any voltage from the coil. also it seems the problem is with the distributor is there a sensor affiliated with the distributor or when they go bad what symptoms or how do the distributors go bad.
any feed back would be a great help
thanks

 

How did you check the CPS? Ohms test or voltage test? Ohms test is not reliable. Voltage test is.

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

 

yeah i did the ohms test i shall test it with the volts test. one thing i forgot to add was the reason why i was posting this thread is because nowhere did i find anyone who got their xj to start randomly and then nothing again.
i shall test the cps again but could the cps fail intermittently?

 

Yes, they can fail intermittently. And also, if the output voltage is low, at the threshold, they will start sometimes and not others. CPS signal strength must be established before proceeding further.

 

well i replaced the cps anyways because at my mileage im going to assume it would go out soon anyways. also its only 26 bucks. still no start. i then as i was double checking the plug on the cps i noticed the ground on the firewall to the valve cover bolt was completely disconnected. i thought for sure that has to be it but no. i double checked that it is grounded and it is. i am completely stumped

 

i mean there's really no wrong way to replace the cps right? just unbolt the old one and bolt on the new one right?

 

Yes, as long as the factory special shouldered bolts are there. Do you have the ability to test the CPS with a meter? We've seen quite a few weak ones right out of the box. How are the dizzy cap and wires? They're supposed to be changed every 30,000 miles along with the plugs.

I know you changed the coil and it started. Did you try 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

 

this may or may not be the problem but since you said you broke a vacuum tube I'll chime in: just had this problem after I replaced my fuel injectors, I accidently broke my MAP sensor vacuum tube at the point it inserts into the throttle body assembly and it would turn over but not start. Plugged it up and it started but I replaced the hose with 1/8 hard flexible vacuum tubing from autozone yesterday and it starts like it was new. Without the MAP sensor getting a vacuum u won't start or you might sporatically. Look in Haynes manual 6-8 under emmissions and engine control systems it maps it out. I drive an 89 so Its probably the same set up but the piece of hard tubing that fits onto the sensor should be salvaged because you can't remove that rubber fitting. I spliced the original and new pieces together.

 

Had a similar problem recently with my '96 Xj. Went through a bunch of electrical troubleshooting and I was able to determine it was a bad fuel pump. Replaced the fuel pump and filter and have been running since.

 

The sensor inside the dizzy will not cause a no-start on a Renix Jeep.

I'm with jwl89xj on checking the MAP hose from the throttle body to the sensor on the firewall. If there's a big vacuum leak, it can no-start due to a super rich mixture.

 

Does all of your lights come on the dash when you turn the ignition?

 

what hose is it to the map sensor

 

Turns out it was the icm. Runs great meow.