wim

I am trying to sort out my 97 XJ ,s last problem . The vehicle is in an overall excellent condition , but driving under hot conditions and making it work , it suddenly cuts out . The engine cranks but fails to start. Temp gauge shows normal and sitting around for anything between 10 and 30 minutes it will start and go untill the next labouring session. It happened once while at my local Jeep expert and subjecting it to a diagnostic test showed up the Crankshaft Sensor. After a few minutes it started and the diagnostic test was clear.
Question : from my driving experience with this condition it appeared to me clearly as a temperature related problem . I have read up the working and function of the Crankshaft Sensor and fail to see the relation of this part to be malfunctioning due to over-temperature , in fact I do not understand a possible relation. IS THERE ANY ?
The reason I ask , is here in South Africa they charge ± USD 400.00 for a replacement part and the the labour comes on top. For a pensioner since '98 that is load of money and I want to be sure . Love my XJ.
Can anybody advise TKs

BlueRidgeMark

Yes, heat can definitely affect the CPS. It's a well-known issue.

Next time it gives you a problem, hit it with and see if the problem clears.

For sensors, only use NTK/NGK brand. These Jeeps are picky!

Ralph77

I believe that my CPS was making my Jeep stall for that very reason. Can read about my issues here:

https://www.cherokeeforum.com/f2/cut...riving-241745/

tjwalker

Absolutely the crank sensor can suffer "thermal failure" (heat related). I've seen it countless times.

Best choice for a new crank sensor is an OEM Mopar unit from Jeep (if you can find one). There are plenty of crank sensors that aren't worth the box they are packaged in.

Good luck and keep us updated!

wim

The feedback from three CF Veterans certainly puts my mind at rest that I am not been taken for a ride . I thank you from the bottom of my heart that you took the trouble to reply that quick . I will certainly try that trick with the coolant spray while trying to locate a replacement part in the meantime.
I also work on my XJ rather regularly, that is part of the fun , but can be challenging at times. Excuse my ignorance , but how do I close this thread?
Kind regards to all , Wim

BlueRidgeMark

No need.

Actually, we really would like it if you would report back and let us know if the problem is solved.

MonacaYankee

I had the same symptoms 1 year after replacing the cps in my 94, the ignition coil went bad..

tjwalker

That is a valid point and the ignition coil can suffer from thermal failure.

But the OP noted that diagnostics pointed to the crankshaft position sensor (lack of crank signal on a scan tool I assume as engine died), so that along with thermal failure makes the crank sensor the most likely root cause for that vehicle.

Both the coil and crank sensor can be tested but you would have to test them when they are in a failure mode (and quickly before they cool down) as they will almost assuredly test within spec when the engine actually runs.

wim

Dear all
Thanks also for the inputs from Monaca and TJW.
What I intend doing is going on a camping trip the 22- 26th this month prepared with a coolant spray. Pulling a ± 1 ton trailer will certainly bring up the problem and I will keep the coolant close by ! BlueRidgeMark -- you guys are just so nice -- I will definitely give feedback.

Knucklebuster

I replaced my Crankshaft Position Sensor at 260,000 miles because of a recurring check engine light (Code PO320) and hard starting. Still had same problem. I have a 2 channel oscilloscope and checked the Crank Sensor signals at the sensor and the Engine Control Module. Both signals were fine.


Watched U Tube videos on the subject and was directed to check Cam Position Sensor. I checked signals with the scope and found a spike and a dropoff on the signal. Replaced the sensor. Still no fix. Finally I rocked the distributor shaft and found the shaft bearings were shot, The shaft carries the tone ring for the Cam Sensor and the rocking gave a dirty signal, causing the hard start and check engine light. Replaced distributor and the problem was solved. Things aren't always what they seem to be.

BlueRidgeMark

Yep, I went down that same road, only it was the dealer that figured it out.

97grand4.0

Cam sensor is almost the same type symptoms of failure as the CPS. If $$ is the issue you want to be as sure as possible. Would be nice to have a code, they do throw codes you know, but not always.. I would be looking at fuel pressure as well.
As mentioned you want Mopar only on these sensors, aftermarket will just add headaches. I ended up with 2 aftermarket cam sensors, both caused..hard starts and rough running..Even a new distributor came with a junk cam sensor..So I went to the junkyard and pulled a Mopar cam sensor. That was 2 years ago and still running strong.
I would add that the typical symptom for a CPS or cam sensor failure is hard starting, more than cutting out.

wim

Update: Came to the conclusion that even though the Jeep was registered as a '97 it is actually a '96 (according to VIN and body style, etc.). The famous "bastard" year! The PDC matches that of a '96 Grand Cherokee (with main fuses in different position) but the wiring color-codes are different. Instrument cluster is same as pre '96 (analog trip (odo) meter). It is an OBD2 system (which matches the year 1996).

On the dash was an after market temp gauge installed as stock gauge was not working. Also installed on T-stat housing was an after market temp sensor (drilled into flat part of T-stat). Found out that the reason the stock temp gauge did not work was because the block does not have a place for the temp gauge sensor (at rear of block). So it seems the engine block was at some stage changed from a '95 to a '97 block (which does not have the rear temp sensor). The stock connector (for temp gauge) was removed at some point and the wire extended to reach the after market temp sensor on T-stat (found the wire tucked away on fuel rail when looking for the stock connector).

Also removed the CPS to check part number (which is #56026921) and therefore pre '96.

From testing the stock gauge with the after market sensor the engine runs from a 100 to around 110 without efan coming on which seems to indicate that the gauge shows a bit too much (temp wise) and to be expected as it is not the usual Jeep sensor. The after market gauge on the other hand shows the engine running between 80 and 90 which seems to be a little less than actual? Have tested the PCM ECT sensor (ohms) and seems normal (when engine is cold and when hot) but need to be sure! Any suggestions on finding the correct temp? Have tested the efan by disconnecting the ECT sensor when engine is running and PCM switches efan on. Also comes on when using A/C.