1994 XJ 4.0l lambda sensor mystery

[michaelc291]

Hello,
I will be fitting a new cat shortly and may have to fit a new rear, (after cat) oxygen sensor if the current one gets broken.
I have hunted high and low but can find nothing like the one currently fitted so can someone please help.
Apart from the baffling number of choices and equivalent information which seems to differ depending on where you look I am still none the wiser.
As the picture shows it looks normal enough at the bottom end, but there is no connection nearby instead it goes up past the starter motor picks up the hood release cable in a conduit and goes inside behind the dash.
There surplus length is coiled up and the plug connects to a little black box. The cable must be at least 2 metres long.

Does anyone know what I have got and where can I find one? All suggestions welcome.
Thanks
Mike

 

[michaelc291]

I have been advised that this is not an oxygen sensor but a temperature sensor. The mystery is why it is fitted to my Jeep when after cat oxygen sensors did not come in till 1998. I can find no mention of temp sensors.
I don't know its purpose. Is it simply to warn of high exhaust temps or does it go to the ECU and control he injection? Does anyone know?
To confirm that it is a temp sensor check this out:-
https://www.aliexpress.com/price/exhaust-gas-temperature-sensor_price.html?src=google&albch=search&acnt=479-062-3723&isdl=y&aff_short_key=UneMJZVf&albcp=266121556&albag=7593673036&slnk=&trgt=dsa-42862830006&plac=&crea=64152518716&netw=s&device=c&mtctp=b&memo1=1t3&aff_platform

The problem now is which one is it? All suggestions welcome.

 

[TerryMason]

That looks alot like the cat in this 1996. Are you sure that it's not an O2 sensor?

 

[michaelc291]

I have been given the following Jeep part number 52079197 which comes up as a temperature sensor for a RHD European spec on a Mopar site but I cannot see any further details.
Rear O2 sensors did not appear till later.
Comparing the pic above to what I have shows a much fatter item, mine only measures 3mm dia just behind the 17mm hex nut and has a non detachable 3m braided cable only 4mm dia.
I need details for the temperature probe to do a fitment check on the new cat which is M18 x 1.5.
I also would like to know why it's there and what it does and can anyone find one for me or point me in the right direction?

 

[michaelc291]

I have given up trying to find this part despite days of searching so here is what I have done.

For Jeep Cherokee XJ fitted with
​

after catalyst Temperature Probe
​

Some European specification RHD Cherokees have been fitted with a temperature probe where an after-cat lambda/oxygen sensor can normally be found.
The temperature probe is now an obsolete part so an update is needed.
After 1996 the whole system changed and two lambda sensors were fitted. If you need to change the cat or even the probe this will outline what I had to do.
Firstly, you cannot buy a replacement cat for a temp probe.The thread is NOT M18 x 1.5. If you order one by model and year for your car it will come WITHOUT a welded on boss, so buy one with a boss and save the hassle of having to buy it separately and weld it on yourself (like I did).
The temp sensor is a K Type EGT (exhaust gas temperature)and can easily be found on Ebay. Ensure it has a 3m (9.8 ft) cable and afitting on the probe with a 1/8 NPT male thread. Buy one with a 90deg bend soit sticks out less under the car. It should look a bit like this and will costless than £5 ($6 or €5.70) incl p&p.

There will be no plug on the end so use the old one and follow the colour code of the wires. Solder the connection and put heat-shrink overthe joint. Do the joint a couple of inches (50mm) from the plug.
Next you need an M18 to 1/8NPT Adaptor. Again, you can find these on Ebay described as a sump (oil pan) plug adaptor. I got a brass one for £12 ($16 or €13.70) incl p&p.Itlooks like the one above.
Now all you have to do is put it all together.
Having sorted all that out there is, however, one remaining problem. Can anyone tell me what the darned thing actually does?
This information given above is given in good faith based on my personal experiences and is intended as guide only. Please do your own checks prior to starting work. Vehicle details may differ.

 

[michaelc291]

The pictures that should have appeared above are here.

 

[TerryMason]

If you just unplug it, do you get codes, or poor mileage / performance?

 

[michaelc291]

I have not tried this yet as it means removing panels etc. I have the dreaded Test coming up on 21st for re-plating the car from UK plates to Spanish.
Everything sees to be working OK at the moment so I'll have a look after the test is done. I will also get an idea of the exhaust pipe emissions as that is part of the test.Unfortunately I don't have my own tester.
There is no plug-in facility for getting the codes. Will the older 'count the flashes' system pick up anything if I disconnect the sensor?
Thanks
Mike

 

[michaelc291]

I have upset something. after fruitless attempts to get the sensor out of the cat I resorted to WD 40 and then my old faithful penetrating oil, diesel, which I have used for years on seized components.
Today the engine cut out dead on a roundabout. It restarted OK seconds later. Driving back home the 'check engine' light came up and it shows a 21 code for oxygen sensor.
Is it possible that WD40 or diesel have got into the sensor and shorted it. I assumed these things were watertight or could it be coincidence that the front one has suddenly given up?
Where is the best place to start checking?