FWIW a faulty coolant temperature sensor will not cause the ECU to cut spark nor fuel however it WILL cause the ECU to thing you're on the north pole and dump tankerloads of fuel into your cylinders during cranking which will more often than not prevent an engine from starting.

OP, this sensor can NOT be your issue if you have no spark.

There's not a lot to it and pretty much all bases have been covered by the previous suggestions here.

If you are 100% certain you have followed ALL the recommended tips here then the last thing is the worst thing.

Start testing EACH and EVERY relevant wire. One at a time with a VOM for the proper resistance, shorts and or crosses.

That is the worst.

These rigs are going on 30 years old. Wiring failing can and does happen. More often than not due to improper routing at sometime during a repair job but sometimes they just fail due to old age, vibration and sometimes crappy insulation quality.

Anything can be fixed, it just depends on how persistant, thorough and stubborn you are.

 

Yes-To agree with Firehawk, it's most likely something basic like a short or completely failed component. Bad ICM/Bad Coil/Bad wiring. This should be the easiest to fix really.


I would suggest getting a buddy to turn the key while you're in the engine bay wiggling every connector around the ICM etc. Even with a really weak CPS, a lot of times you will get the engine "catching spark" and trying to run. If it's just turning over and you have fuel going in that's almost a 2 out of 3.
Five bad plug wires and it would still go every sixth revolution. If the plug wires were all out of order, it would still kick.


If you remove the coil completely, you would need 12V to the prongs. If there's no voltage there, then it's a bad ICM or the wiring to the ICM is bad. That's the only thing I can think of at this point. If no 12V at prongs then no volts to coil and then that would be a no spark for sure. That's an easy check.

 

Link to a factory service manual!!


http://oljeep.com/89FSM/89Jeep_FullServiceManual.pdf


It's for an '89 but should be helpful.

 

Ok cool im going out right now to check the ICM and the wires. Thanks for the help guys.

 

Ok I just checked the contacts on the icm with the key to the accessory position and it read 4.7VDC and 0ohms between both contacts.

 

Between the two contacts as in where the coil seats? If so...issue. should have 12.6 vdc there. Also, is your fuel pump priming when you turn the key to run? If not, try jumpering the a) fuel pump ballast resistor and b) the b+ latch relay (also called the Asd relay)

 

yeah between both contacts. i have a pretty modern multimeter so it reads the ohms when i go between the two contacts. But yeah about 4.7VDC on the contacts.
Yeah the fuel pump is priming before i start her up.

 

Just for **** and giggles try key in run position to confirm same as first reading.

 

I'm assuming he meant "RUN" position because the ignition shouldn't be powered up in ACC at all. According to the FSM, there's only 5 volts at the coil as far as I can tell. I always thought there should be 12. If he has voltage there, with the coil removed, if he keeps the meter on the prongs and someone else turns the ignition switch to start, he should see 5V fluctuating there as engine turns. The FSM says it's a 5V square wave so that should mean it goes from 5, holds and then goes to zero. I've never done this so I can only assume that's what would happen. I'm thinking bad coil. Surely this could be diagnosed by a mechanic with a scope.


Trovilci-Be very careful working around this area if the coil is attached. There's high voltage there. If you aren't sure of what you're doing, take it somewhere to have it checked.

 

Ok well heres whats going on. For S&G's i took the ICM to Advanced Auto to have it teted and it wouldnt even pass the first 2 of 10 tests. So thats telling me its bad. Funny thing is the lady at AA quoted me a price of $128.99!!! I was like holy cow. Before i went i checked out my local NAPA online price and they are quoting $58.95. Thats like $70 off. WTF may i ask. The lady told me she didnt know what to say, and that she would go to NAPA herself. lol. So i contacted Davy's Jeeps cause they live 2 hours away from me and they quoted $40 shipped. Im prolly gonna go with NAPA for $10 more and pick it up. Seeing as it would be brand new from a reputable company and i only live 10 minutes away. So now let see how this works and if this truely is the culprit. Again just say again thanks everyone. I really appreciate the help with this. Ill get back to you guys ASAP.

 

I have serious doubts about any bench testing done at Advance/Oreilly's/Schucks auto.........Especially a relatively rare Renix related part.

 

Me, too. I'd like to see their testing protocol.

 

I actually was helping the test the ICM. The actual image on the procedure was the same "Made in France" one we were testing. They looked completely identical. I really dont know if it would actually tell the true results or not but i know we ran the tests 6 times and it failed every time. Maybe the test was true i really dont know but could a jeep that ran perfectly fine when i first got it have failed wires or broken connections due to driving for 15 minutes? All i changed was the spark plugs, how the hell does it fail and not start after that? They were gaped to .70. Anyways trust me im not doubting anything you guys are saying just from my experience with mechanics and stuff i have never heard of this happening. If the coil reads 4.7 VDC, then thats a failed condition right? I have already checked all the junkyards and pick and pulls around where i live and no one has any ICM for the renix engines. Im probably gonna have to order one.

 

Welp, if you're only getting 4.7V to your coil then I really doubt the ICM is your issue. I am looking at a schematic and it shows 12v to one of the two yellow wires, but hey, how could that just randomly go bad if all you did was change the plugs and drive it 15 mins, right?

There's no way your doing stuff under the hood could have damaged a 25 year old harness.

 

I'll take a picture of the one in my store for ya tomorrow, it's essentially a brain box you hook the icm up to, tests it through high/low ranges, and several others. And yes, they do have an old renix connector, granted the one my machine uses is just an old serial cable, with the individual pins terminated in alligator clamps for the icm contacts. But yea, they do exist!