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Mechanic's Riddle... Random 'dummy light' problem

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Old 03-30-2015 | 08:22 PM
  #16  
beyondkreativ's Avatar
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Year: 1997
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Engine: I6 4.0L
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Originally Posted by Larry's XJ
What brand temp sensor did you use? That may be the problem.
How are you verifying "real" temps? IR, mech test gage, thermometer in rad?
The temp sensor is a BWD from advance auto parts. One of the mechanics I have paid to diagnose this problem hooked up a computer through the OBD in the Jeep. The readings have been verified by 2 other mechanics that tried to figure this problem out. Though I don't know by which methods they measured the temps.

I am picking up a cluster with a temp gauge tomorrow so that I can monitor the temps myself, while I'm driving.
Old 03-30-2015 | 08:32 PM
  #17  
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Originally Posted by CCKen
How did you check continuity from the cluster to the sensor? The ECT sensor signal goes to the PCM, not the cluster.


Why did you replace the ECT connector?


Does your radiator electric fan kick on when the temp jumps to 308 degrees?


It sounds like you are getting an open in either in the live ground network wire to the ECT (Brown/Yellow tracer wire) or an open in the signal wire to the PCM (Tan/Black tracer wire).


Inspect the ECT wires where they enter the fuel injector wiring manifold for defects, and inspect the wire loom where it exits the manifold for chafing through to the wires within. There have been a few reports of the loom chafing on the end of the fuel rail.


The ECT Brown/Yellow tracer wire splices in to the ground network inside of the fuel injector manifold. If you can't find any obvious defects in the wiring/looms outside of the manifold, open the manifold and look for the splice. Check it.


If all else fails, wiggle the wiring harnesses while observing the coolant temp on your scanner to see if it jumps.


I could show you how/where to check voltages at the ECT connector but do the above checks first.

I will try to answer your questions as best I can.

--I did not personally test the continuity from the cluster to the sensor. The most recent mechanic that looked at it told me that he pulled the dash apart and checked the continuity from the cluster.

--The connector to the sensor was replaced because one of the guys that looked at it thought the wires could have been broken where they were bent into the connector. The connector came with short wires coming out of it.

--Yes, the electric radiator fan does kick on.

I will check the wiring myself that you mentioned and let you know if I find anything. Tomorrow I am installing a new cluster, with a temp gauge, so that I can monitor the temp more accurately.
Old 03-30-2015 | 10:33 PM
  #18  
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If the fan turns on then the problem is between the ECM and the sensor.
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