I believe you mentioned you suspected an issue with the power relay as you said it was very hot. Maybe it's normal as it is always powered. It means you have power to the tranny module. If you got home after a failure and you limped home, I would suspect eh relay to be cold, unless the problem was in the module itself...being powered by the relay but not interacting with the tranny.

 

 

What color was the base of the power relay?

 

Any update to this? Just curious as I sit at home.
So, looking at the wiring again, it appears that as long as there is battery power and power from the inertia switch output, the tranny control module (TCU) is receiving power. So, the relay would be hot/powered all the time as long as there is power to the car and it's running (The inertia switch supplies or removes power to the fuel pump to kill the engine in a crash). I would suspect they wanted the tranny de-powered also as it's on the same power leg. So anyway, it looks like the TCU can go into fail mode even while the relay remains powered. The tranny and the TCU communicate together so either something is going on with the tranny, (maybe the speed pick-up) or something with the TCU itself. I believe the tranny electrical connector can be removed, inspected , cleaned and reinstalled. Maybe dirt or corrosion on the elect connector pins.

 

Y'all are amazinng! Just had to throw that in!

 

I replaced the relay, but it kept going into limp mode for a week, and I remembered my XJ40 doing it to me also a couple of years earlier. So I drilled two snakebite holes underneath the TPS housing(lowest point) inserted the straw end of electric cleaner spray into one of the drilled out holes and cleaned the TPS. The dirty oil deposits came out through the other hole. Once dried, I reconnected the battery and it cured the problem. So a fouled up TPS was the culprit. The two small holes are there to allow oil to drip out and not pool inside the housing. I should clean it again this summer. The car. now has about 191k miles, and its not slowing down anytime soon.

 

Oh, so hard shifting and tranny going into limp mode is solved? It was the TPS? (Throttle Position Sensor) on the throttle body?

 

it was a dirty TPS. XJ40s are known for having that issue. Its due to its position. Its plastic and easy to drill, so be careful, and just tap through.

 

I am having the same transmission problem with my 1994 XJS. Replaced the relay and the the problem persists. Have you solved your problem? How? What is the location to the TPS on an XJS?

 

Yes, mine was a dirty TPS which is known to cause trouble due to its placement on the throttle body. Here’s a link that discusses the issue for a member who went through the trouble of removing the TPS. I explain that strategically drilling two snake bites at the lowest point, will make it easy to clean.
https://www.jaguarforums.com/forum/x...00-rpm-247683/