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  #1  
Old January 19th, 2011, 11:59
Rhys898 Rhys898 is offline
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Ignition issues on 1990 Jeep Cherokee Laredo 4.0L

Hello Everyone,

I have a 1990 Jeep Cherokee Laredo 4x4 with the 4.0L motor and NP242 transfer case and 4 speed automatic transmission. Every six months to a year for the last 3-4 years I have had to play musical coils to get the car to run. I have 4 total now that all test the same or very close to the same with a multimeter but sometimes they would work, sometimes not.

About a month ago the Jeep stopped running all together, thankfully I was at home when it failed to start and I was able to borrow a car from my dad.

The first thing we replaced was the 5-6 year old Crankshaft Position Sensor with a new Standard(brand) one since the musical coils didn't work. When that did not solve the problem we replaced the coil again with a brand new Bosch. Still didn't work. Got an Intermotor Ignition Control Module. Car started fine in the driveway, ran to go to the store and back, ran to a friends house. After being parked for an hour we headed back home and got about half way when the engine died at 35mph on a down hill. Came to a stop at a busy stop sign but was unable to get it started again.

Got the car towed back to the house the next day and after futsing with it for an hour or so my room mate got it running again. Turned it off, left it for 15 minutes, started right up again. Next day went to use it, wont start again.

Battery and alternator are good, we have fuel pressure at the rail, but are not getting a spark.

My mechanic room mate and I are at our whits end.

Any Help GREATLY appreciated.


Jeremy
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  #2  
Old January 20th, 2011, 08:33
joe_peters joe_peters is offline
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Re: Ignition issues on 1990 Jeep Cherokee Laredo 4.0L

Grounds.

1. Replace the POS braided strap from the head to the firewall with a 4 or 2 gauge cable. Strip the metal bare, treat with an anti-corrosion agent, make the connections TIGHT.

2. Dipstick tube grounds--ECU, ICM/coil, o2 sensor, others. Strip to bare metal, treat with an anti-corrosion agent, make the connections TIGHT.

3. Contact clips between the ICM and coil. Clean them, treat with dielectric grease.

4. Clean the contacts at the B Latch and fuel pump relays, treat with dielectric grease.

Post up results.
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  #3  
Old January 20th, 2011, 10:30
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Ecomike Ecomike is offline
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Re: Ignition issues on 1990 Jeep Cherokee Laredo 4.0L

Explain "Musical coils"? What coil(s)?
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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Old January 20th, 2011, 11:30
Rhys898 Rhys898 is offline
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Re: Ignition issues on 1990 Jeep Cherokee Laredo 4.0L

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Originally Posted by Ecomike View Post
Explain "Musical coils"? What coil(s)?

I have 4 ignition coils that I have purchased over the last 4 years, three test identical, and one tests almost the same as the other three when testing with a multimeter based on the haynes manuals instructions. There have been times when I tried the 1 or 2 spares that I had on the shelf, and none of them worked, bought a new one, that one didn't work, tried one of the old ones again, it fires up and runs no problem for 6 months.

Thanks for the replies, I'm going to go get some dielectric grease, and some heave gauge wire to use as grounds, what kinda of anti corrosion agent do you recommend?
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  #5  
Old January 20th, 2011, 11:35
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Ecomike Ecomike is offline
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Re: Ignition issues on 1990 Jeep Cherokee Laredo 4.0L

You have been replacing the wrong part. You have a borderline wiring, possibly ground, or marginal CPS, or all of the above problems.
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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  #6  
Old January 20th, 2011, 14:04
Rhys898 Rhys898 is offline
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Re: Ignition issues on 1990 Jeep Cherokee Laredo 4.0L

At this point I'm pretty sure it's wiring and or ground. The CPS is new, as are the currently installed ICM and Ignition Coil. Later today or tomorrow morning I will be replacing all the grounds with 4 gauge wire.
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  #7  
Old January 20th, 2011, 14:20
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Re: Ignition issues on 1990 Jeep Cherokee Laredo 4.0L

RCBRC= Refresh Connections Before Replacing Components. This should be the Renix mantra...........
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Old January 20th, 2011, 14:38
joe_peters joe_peters is offline
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Re: Ignition issues on 1990 Jeep Cherokee Laredo 4.0L

You can get an anti-corrosion agent at any paint/hardware store.
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Old January 20th, 2011, 15:46
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Ecomike Ecomike is offline
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Re: Ignition issues on 1990 Jeep Cherokee Laredo 4.0L

Have you tested your CPS cranking voltage? Mine is new also, and it was still a problem!

http://www.naxja.org/forum/showthread.php?t=1050783

http://www.naxja.org/forum/showthread.php?t=1051325
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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  #10  
Old January 20th, 2011, 15:49
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cruiser54 cruiser54 is offline
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Re: Ignition issues on 1990 Jeep Cherokee Laredo 4.0L

Quote:
Originally Posted by Ecomike View Post
Have you tested your CPS cranking voltage? Mine is new also, and it was still a problem!

http://www.naxja.org/forum/showthread.php?t=1050783

http://www.naxja.org/forum/showthread.php?t=1051325
This is a good idea. We found when these were new that under 350MV from the CPS caused intermittent starting problems.
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  #11  
Old January 20th, 2011, 16:56
ChicksDigWagons ChicksDigWagons is offline
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Re: Ignition issues on 1990 Jeep Cherokee Laredo 4.0L

I didn't hear a mention of the hall sensor in the distributor. If all else fails, I'd look at this. Sounds like everything else has been covered. Good luck!

Oh, also pull your ECU and check the connector for corrosion. I had one that somehow got damp and was growing green corrosion. Not good as you can imagine.
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  #12  
Old January 20th, 2011, 17:09
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Re: Ignition issues on 1990 Jeep Cherokee Laredo 4.0L

I like the idea of pulling the ECU and refreshing the connectors.

The stator inside the distributor only controls the sequential firing of the injectors, and if faulty on a Renix motor will not keep it from starting or running.
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  #13  
Old January 20th, 2011, 17:12
joe_peters joe_peters is offline
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Re: Ignition issues on 1990 Jeep Cherokee Laredo 4.0L

Quote:
Originally Posted by ChicksDigWagons View Post
I didn't hear a mention of the hall sensor in the distributor. If all else fails, I'd look at this. Sounds like everything else has been covered. Good luck!

That is because it is the synch sensor that feeds cam position data to the ECU for the injector firing pulse and, on the Renix, will not prevent the engine from running nor will it effect spark.

Oh, also pull your ECU and check the connector for corrosion. I had one that somehow got damp and was growing green corrosion. Not good as you can imagine.

Been taking the XJ swimming?
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  #14  
Old January 20th, 2011, 21:02
ChicksDigWagons ChicksDigWagons is offline
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Re: Ignition issues on 1990 Jeep Cherokee Laredo 4.0L

Good point!

And surprisingly no, this was a stock XJ I picked up as a non-runner. No other signs of it having gone swimming. Very strange.

Another thing worth looking at, I just went through this with mine actually. I had a bad T-stat, stuck open, and it would run okay as long as I was under load. Fuel economy was nasty though cause the engine never got up to temp. Now if I stopped and let it idle for any length of time, particularly on warmer days, it would flood and die. And it wouldn't start unless I let it sit for a good long while. I too thought coils and swapped a known working coil/ignition module. It started right away. Thought it was the silver bullet. Few days later, same thing.

Had me scratching my head. Eventually I figured the coolant temp sensor for the ECU was reading so low it was dumping fuel like it was in warmup-enrichment mode. But the combustion chamber was fully up to temp even if the coolant wasn't. Flood out. Change T-stat and runs a champ now.

So if your t-stat is working fine, it might be worth testing the sensor. I think that one is under the manifolds on the side of the block?
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  #15  
Old January 21st, 2011, 12:15
Rhys898 Rhys898 is offline
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Re: Ignition issues on 1990 Jeep Cherokee Laredo 4.0L

ok guys, as of right now, I have not driven it anywhere but it is starting reliably.

I checked the resistance on the new CPS and it was reading 208, so I plugged it back in and tried to start it. It turned over but still no spark. My room mate un-bolted the ECU and pulled it down into the foot well and checked the connections, no evidence of corrosion and he reseated the cables. While he was doing that I jumped the two conductors on the CPS. Since then the car has started every time. We also checked the grounds and all of them were tight and showing good ground.

We are going to start it and let it run for a couple minutes every hour or so and if it continues to start till this afternoon we will put the ECU back and I will try taking it around the block, let it get up to running temp and see if it dies on me.

I'll update later tonight or tomorrow.

PS I checked the old CPS and it is showing 225ohm resistance so it's most likely still good. We will probably re-adjust the new one since it is slotted where the old one is not.
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