Help! Jeep gets to operating temp then shuts off (no check engine light)

Kraig

Kraig

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New Jeep owner looking for help. I just got a 97 wrangler 4.0 5 speed. When I got it the intake manifold wasn't seated properly and would go to the rev limiter as soon as you started it. So I put a new intake/exhaust gasket on and reseated it and put it all back together. It started right up and seemed to run great. The problem now is that as soon as it reaches operating temperature it acts like it's starving for fuel and shuts off. Then it will only start and run for about 1 or 2 seconds then shuts back off. There is no check engine light or any codes being thrown. I can hear the fuel pump cutting of when I first turn the key and it has good fuel pressure. It has new plugs, wires distributer cap and rotor. I'm not sure where I need to go from here. Any advice is appreciated.
 
Are you 100% sure you got that intake / exhaust manifold gasket seated properly? I know that can be a real pain in the butt to get seated correctly.
 
Chris said:
Are you 100% sure you got that intake / exhaust manifold gasket seated properly? I know that can be a real pain in the butt to get seated correctly.
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It looks level and centered and I used a thin layer of sealant. It runs, revs, and idles great until it's about 190 degrees. Is there a specific way to check for leaks, or just spray something like carb cleaner around the manifold while it's running? Should I do it while it's cold and running good? Or wait until it chokes itself out then spray while turning over?
 
Kraig said:
It looks level and centered and I used a thin layer of sealant. It runs, revs, and idles great until it's about 190 degrees. Is there a specific way to check for leaks, or just spray something like carb cleaner around the manifold while it's running? Should I do it while it's cold and running good? Or wait until it chokes itself out then spray while turning over?
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Yes, if you spray something in there like SeaFoam you should be able to see where it comes out of if there is a leak. I'd do it while it's cold and running good.

Another thing: The number one cause of thermal (heat related) failure on the 4.0 is the crankshaft position sensor. The problem is that the internal resistiance changes when the sensor gets hot, sometimes it completly disconnects or shorts. that will affect the output of the sensor, to a point where the PCM can't use the signal, and the engine dies. When it cools of, the signal is within the tolerance and the engine can run again.

If you end up replacing the CPS, be forewarned that unless you use a OE Mopar sensor, you're likely to have issues with it, as our Jeeps are notorious for rejecting sensors other than OE Mopar ones.
 
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Chris said:
Are you 100% sure you got that intake / exhaust manifold gasket seated properly? I know that can be a real pain in the butt to get seated correctly.
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Typically the consequence of not doing so is obvious and immediate. It hits the rev limiter as soon as it fires up. Your second guess is much better. Replace the CPS, you need a spare anyway.
 
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Chris said:
Yes, if you spray something in there like SeaFoam you should be able to see where it comes out of if there is a leak. I'd do it while it's cold and running good.

Another thing: The number one cause of thermal (heat related) failure on the 4.0 is the crankshaft position sensor. The problem is that the internal resistiance changes when the sensor gets hot, sometimes it completly disconnects or shorts. that will affect the output of the sensor, to a point where the PCM can't use the signal, and the engine dies. When it cools of, the signal is inside the tolerance and the engine can run again.

If you end up replacing the CPS sensor, be forewarned that unless you use a OE Mopar sensor, you're likely to have issues with it, as our Jeeps are notorious for rejecting sensors other than OE Mopar ones.
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I suppose you like ATM machines and VIN numbers as well?
 
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Chris said:
That one went over my head... :D
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You are fond of Automated Teller Machine Machine and Vehicle Identification Number Number. CPS stands for Crank Position Sensor. If you tell someone they need a new CPS Sensor, you just told them they need a new Crank Position Sensor Sensor.
 
mrblaine said:
You are fond of Automated Teller Machine Machine and Vehicle Identification Number Number. CPS stands for Crank Position Sensor. If you tell someone they need a new CPS Sensor, you just told them they need a new Crank Position Sensor Sensor.
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Not sure how I missed that. I get it now :risas3:
 
I put a new tempature sending unit in tonight and it seemed to do the trick. Let it warm up and drove it around the block. I will do an actual test drive tomorrow and hopefully it'll be problem solved
 
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Tsu was my first thought as well. It sounded like the issue I had on a car with a slow coolant leak. As soon as it would get too low the car would freak out on hills.

—
There must have been a time
when we could have said no.
 
No there's apparently 2. The one on the back back of the motor operates the temp gauge. The one on the front is the one I replaced.
 
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Kraig said:
I put a new tempature sending unit in tonight and it seemed to do the trick. Let it warm up and drove it around the block. I will do an actual test drive tomorrow and hopefully it'll be problem solved
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Keep us updated on that because simple logic dictates that unplugging the sensor should cause issues with the engine running and I've not seen that before when I've left it unplugged accidentally. That is a good one to toss in the diagnostic bin.
 
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Well went for a test drive after it had warmed up. All seemed good made it about 2 miles down the road and the same thing started to happen. I guess the next step is the crank position sensor? I've also seen a couple other people say it could be the ecm. Is there a way to test the cps before I spend $100 on the wrong part?
 
Set your meter to measure ohms (Ω) . Place your leads across posts a and b of the ckp

You should get 200 ohms plus or minus 75 at operating temp.
Being that yours is intermittent it may test fine when cold.Maybe using a heat gun to replicate conditions?It might also be a broken wire where mechanical movement is causing sensor to fail.
Does the jeep die while just sitting or does it have to be driven?
Every jeep I've owned has needed to have the cps replaced at least once
Had to edit for proper ohms readings.
 
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Imapepper said:
Set your meter to measure ohms (Ω) using the scale between 1K-10K. Place your leads across posts B & C of the CPS plug.

You should get a reading of open or no resistance. If you get a reading of low resistance, replace the sensor.
Being that yours is intermittent it may test fine when cold.Maybe using a heat gun to replicate conditions?It might also be a broken wire where mechanical movement is causing sensor to fail.
Does the jeep die while just sitting or does it have to be driven?
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It dies sitting or driving.
 
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