I have a 96 XJS 6 cylinder convertible where the tach operates sporadically - hit a bump it comes on or sometimes it just pops on and then dies out. The speedometer, odometer and trip meter work fine. When it pops on it looks accurate so I'm thinking a bad ground - anyone have any thoughts as to the first places to look? I'm trying to avoid having to dig into the dash if there are easier access points to check first.

 

Your tach signal comes right out of the ECM and splits to the tach and the Trans Control Module. You don't have any warnings or trans issues, I assume, so it must be a connection near, at or inside the instrument pack. The tach signal goes in on a purple/yellow trace wire at pin 8 of the 18-way connector on the back. There are two Hewlett-Packard connectors there, a 14-way and an 18-way, you want the bigger one.

Hope that helps.

 

Thank you for the response. I downloaded a schematic and you are correct it's the purple yellow combination (not that I doubted you).
I'm tearing into it this weekend so hopefully it will only take jiggle of a wire or removing and re-plugging the HP connectors. Any trick to removing and inserting them that I should know about?

 

Okay, so I looked up her skirt behind the dash. No room to work. there's a brace for the steering column and two bundled sets of wires run north of that brace. I found the yellow/ purple tach wire and traced it to an area any normal human could not easily reach without major surgery.... including the modules.
So, is the answer cut the wrap tape and jeopardize contacts / grounds on the entire bundle / console or look elsewhere. Pulling the dash electronics is more than just unsnapping a couple of modules and I'm trying to keep this thing as original as possible.
I firmly believe if anyone has insight it resides here.

 

yours is a '96 so I'm not 100% sure but on mine you can pull the gauge cluster out, pop off the connectors and spend a peaceful afternoon cleaning the individual contacts on your dining room table.

 

Further observation revealed there is power getting to the tach as upon start up the needle jumps a bit and hovers above the little bar where the needle rests when the key is off - just as the speedometer needle hovers above the little bar on that gauge when stopped at idle.
Anyone have any idea as to where the tach receives data from the engine ( I realize the module is bundled with the speedometer, trip meter and odometer in the rear end, but engine info has to come from somewhere in the engine bay even if it then runs back to the module).

 

I believe I fixed you up with that in the second post........

 

Steve - you did - my fault for not reading thoroughly. I've since done a number of searches to determine ECM location (most searches refer to ECU - assuming it is the same) and I went through the Kirby Palm manual and I cannot locate the ECM. Any help would be appreciated.

 

Attached is an excerpt from a document for the '95 XJS. In it you will find the ECM pinouts and control module locations you need. The Kirby Palm book is really more about the earlier XJS models than your later one; still has good information though.
The ECM is accessed in the passenger footwell, by removing the carpeted metal panel at the "A" post, it's attached to the back side.

Good luck!

 

I appreciate this is an old thread, but...here goes.
My 92 is showing a great difference between the trip odo, and the trip computer meter (centre dash). I can reset the odo to zero and also the trip "dist" on the trip meter when filling up, and after a few kms., there is a variance which gets progressively worse. When you have a dodgy fuel gauge, it's hard to know which of these trip meters is accurate. Presupposing one is and one isn't.
But if both meters get the same signal, why the difference in kms ??
Any thoughts ?

 

El Gato, you might as well pull the instrument cluster out and polish all the contacts in both plugs and the cluster. Not too big a job if you are careful with the plastic, can be done without damaging anything.
Luck, RagJag

 

Gerry, a silly question, but..........you have got the trip computer reading Km and not MLs..?

 

Not silly at all. I have the battery out of mine at the moment (to refit a new fuel sender unit) but if memory serves, the difference in the two trip meters was up more than 100 kms. I assumed (!) that the trip computer was also in kms., and not miles. The speedo dial is kms only.
When I get the battery hooked up I will check your point. Can the trip computer (dist) be flipped between miles and kms. ??

 

Button at lower left [ML/Km] switches between english and metric units.

 

Malc & Steve....
I feel like a complete dolt.
Yes the issue was all in my head....miles vs. kms. Duh !!
No need to worry about making notes about distance covered between fill ups, as I sorted out my fuel gauge...A simple matter of spending major coin and fitting a new sender !
There is no feeling like having a reliable fuel gauge. Well not quite, but you know what I mean.
Many thanks for pointing out the obvious.

Gerry T.