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Unread 01-28-2008, 12:01 AM   #1
nimblemotors
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Engine Shuts off after warms up

I just purchased a '89 Cherokee Laredo with 4.0/auto/4x4
Unfortunately, it stopped running on the way home. The engine dies after it warms up, and won't start up again until it cools all the way back down.
I've scanned about 10 pages of messages and didn't see others with the same issue.

I've had it in my garage and now went through three cycles and by warm-up, it seems to actually get a little hot, about 220-230 I'd guess before it shuts off.
Will the ECU shut it off if it gets hot? There is no spark out of the coil once it stops running. Could it be a simple thermostat failure? The radiator doesn't seem to get hot at all, which leads me to think the t-stat is bad. The heater does work and gets hot, so doesn't that mean the water pump works?
Or could it be something more complex? Appreciate any help.

Jack

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Unread 01-28-2008, 08:09 AM   #2
88XJSport
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Since there is no spark coming from the coil when it dies, this leads me to believe you have a Crankshaft Position Sensor failure.

And since it gets warm, a coolant flush/burp with a new 195 thermostat wouldnt be a bad idea.
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Unread 01-28-2008, 08:16 AM   #3
severous01
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i would have said to check the trans fluid......but you're not computer controlled.

but.....get a new t-stat and new coolant. now would be a good time to clean the system too with a flush and some baking soda. flush again and use coolant next time for a complete acid removal and complete coolant flush.
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Unread 01-28-2008, 08:30 AM   #4
88XJSport
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Quote:
Originally Posted by severous01
but you're not computer controlled.
Whats not computer controlled?
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Unread 01-28-2008, 10:42 PM   #5
nimblemotors
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Crank Position Sensor

I don't think the Engine Computer shuts off the engine when it gets hot.
I've read other posts about overheating engines, so the computer will let it get hot. And after thinking further, it should restart when the temp falls back, but it must get all the way cooled down, so it must be something else.
And from leaving the cap open, the temp gauge shows 210 when the water hardly started getting hot, so I think it reads low, so it isn't really getting hot when it reads 220 or so.

I did an ohm check on the CPS (CKS) it read 125 ohms when cold, when it stopped running I couldn't get a reading on it. So I replaced it. Unforunately I dropped the bolt holding it on inside the bellhousing, DAMN IT!! After a big hassle removing the trans inspection cover and fishing it out with a wire, I got it, and installed the new one.

My test run this evening with the new CPS and it stayed running for 5-10 minutes maybe more after it warmed up, so I think this might have fixed it.
I'll test it again tomorrow when it's not so cold out, but I've got my fingers crossed. I did notice the idle speed changes a lot when moving around the wires, I'm wondering if I need to rewire it like the TSB suggests?? It worked good the way it is for 16 years and 250K miles.

Cheers, Jack
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Unread 01-28-2008, 10:51 PM   #6
CanadianJeep86
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Last time I had a vehicle that did the exact same thing as yours, runs till it gets warm and then dies. Turns out it was the Hell Effect Sensor or whatever the hell its called inside the distributor. Try going to the junkyard and grabbing another one. Worked great for mine and you seem to have the same problem.
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Unread 01-29-2008, 04:30 PM   #7
nimblemotors
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Crankshaft Position Sensor fixed it

So looks like that was the fix. Keeps running now, and I've been driving it around and it hasn't stopped running since I replaced the sensor.

The bad news is I took it in for the smog check, and it failed badly, running really rich with 10 times the allowed CO readings and double the HC readings.
It seems to run good though. I suspect the coolant temp sensor. 02 sensor was replaced 3 years ago when last owner bought it and it didn't pass smog.
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Unread 02-01-2008, 09:30 PM   #8
nimblemotors
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MAP sensor vaccum line

Tested the coolant sensor, it was good. Tested the O2 sensor, it read .1 volts after starting at 1.25. So something was making the computer run it rich.
Tested the MAP sensor, and it read 3.5v, that is the problem. The hard plastic vaccum line had gotten brittle and a crack in it. Patched in a hose where it was bad, and it runs good now. Drove it 200 miles today, 19mpg. Still haven't retested smog, think I'll put some new plugs in it, and some alcohol in the tank just to be safe...
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