Diesel not cranking

[layback40]

Originally Posted by Jonny Jeep

Part number for the coolant temp sensor is 4686192. If you search for that you should find the sensor fairly easily, here's one I found listed in the UK, you can see from the pics that it is the three pin connector.

https://jeepey.com/product/temperatu...j-25d-4686192/

I don't know if the sensor resistance would match that seen for the two pin sensors, or which pins would be used to measure the resistance, but it might be worth checking your current sensor against this chart.

Be careful! There are several different sensors.
I have a 98 with a single sensor & IIRC it has 2 pins. my 2001 has 2 sensors. Again they both have 2 pins. the thread is different between the models. The 98 one is very common.
The sensors have a thermistor in them. They should show 4,000 to 5,000 ohms resistance.
My 2001 had both fail & I was able to cut them open & replace the thermistors. They are very cheap, $1.50 each from electronic parts store.
I think I have made a post about them in the XJ diesel parts thread.

[amlav]

The 3 pin temperature sensor has 2 thermistors inside in series . The signal is connected to the common terminals of thermistors and the other ends are +5 and ground . Don't ask why because don't know but I remeber when I pulled mine apart years ago. Had to get one from a Jeep dealership (spare parts) . I think it was about $70 . If the needle jumps from 0 to 100 (or over 100) than the sensor is faulty . If it drops from 100 to 0 than I would say check the gauge cluster connection or the sensor plug/socket wirring connection .

[Ilya]

Originally Posted by amlav

The 3 pin temperature sensor has 2 thermistors inside in series . The signal is connected to the common terminals of thermistors and the other ends are +5 and ground . Don't ask why because don't know but I remeber when I pulled mine apart years ago. Had to get one from a Jeep dealership (spare parts) . I think it was about $70 . If the needle jumps from 0 to 100 (or over 100) than the sensor is faulty . If it drops from 100 to 0 than I would say check the gauge cluster connection or the sensor plug/socket wirring connection .

Hey! Yes, the temperature ranges from 0 to 100 degrees, then to 50, then drops again. The starter malfunction coincided very strangely. Or even the on-board computer can block the engine?

[amlav]

Start with the easy option . Pull the gauge cluster out (fairly easy) and clean contacts than slide it back in . If still no good than check sensor harness connector for possible broken wiring( sometime wire break due to engine vibration).
Does not cost you any money (unless somebody else has to do it for you ).
If temperature gauge still jumps everywhere than replace the temperature sensor.

The onboard computer (PCM) would not impede you to start the engine if the temperature sensor or circuit is faulty. It will just light up the "Check gauges" or "Check engine" light . Can't remember which one exactly.

It is just a coincidence that you starter motor developed a fault in the same time . It is a bastard of a job to change it (at least on the right hand drive diesel xj's ). Measuring resistance does not help in your case because more likely the starter solenoid contacts are not making proper contact anymore to allow current to flow to the starter motor itself. Had the same issue when I bought my XJ.
This are the fixes I can think of....could be wrong but from my experience your symptoms sounds same with the issues I've had some years ago. Cheers

[layback40]

Originally Posted by amlav

Start with the easy option . Pull the gauge cluster out (fairly easy) and clean contacts than slide it back in . If still no good than check sensor harness connector for possible broken wiring( sometime wire break due to engine vibration).
Does not cost you any money (unless somebody else has to do it for you ).
If temperature gauge still jumps everywhere than replace the temperature sensor.

The onboard computer (PCM) would not impede you to start the engine if the temperature sensor or circuit is faulty. It will just light up the "Check gauges" or "Check engine" light . Can't remember which one exactly.

It is just a coincidence that you starter motor developed a fault in the same time . It is a bastard of a job to change it (at least on the right hand drive diesel xj's ). Measuring resistance does not help in your case because more likely the starter solenoid contacts are not making proper contact anymore to allow current to flow to the starter motor itself. Had the same issue when I bought my XJ.
This are the fixes I can think of....could be wrong but from my experience your symptoms sounds same with the issues I've had some years ago. Cheers

Engine will normally start without temp sensor plugged in so can try that to see what happens when not connected.
Need to see if you can hear the starter solenoid clicking.
I have the cap on the relay loose so I can take it off & press the flapper down without touching the key.
I agree that all leads need to be taken off & cleaned with a wire brush or emery paper.
There is one lead on the solenoid that goes into the starter. That was the one that needed cleaning on mine.

[Ilya]

Thanks for the advice. I rang the wiring from the sensors to the on-board computer, it is in order. But I will disassemble the dashboard on the weekend. Yes, you are right, removing the starter is very difficult: you will have to remove one engine mount and the oil filter.
Maybe next week I won't have so much to do at work and I can drive the patient to the lift ...

[layback40]

Originally Posted by Ilya

Thanks for the advice. I rang the wiring from the sensors to the on-board computer, it is in order. But I will disassemble the dashboard on the weekend. Yes, you are right, removing the starter is very difficult: you will have to remove one engine mount and the oil filter.
Maybe next week I won't have so much to do at work and I can drive the patient to the lift ...

You dont need to remove starter or engine mount!
It comes out from underneath.
Use 1/4" drive socket for most nuts & bolts.
Its tight a fit & difficult.