Well...I'd finally gotten my car o the point that EVERYTHING worked properly...for exactly one week.

I was driving home from work and checked my average mileage...1.3. Pretty sure I didn't blow a fuel line since I'd have emptied 3 tankfuls on the way home from work (and the gauge didn't budge). Checking fuel used showed it basically ticking up like seconds on a clock.

Where does the computer get its' mileage input signal from? ECU? Everything else seems to be working fine, distance, av spd, clock, etc.

Any ideas? This is going to bug the crap out of me because it's now the only thing not working on the car...at least for another week...

 

In the trunk (left side as I recall) there is the "fuel interface unit". It take injector pulse info from the ECU and translates it into some sort of signal that the trip computer can read.

Not sure how it could be tested or, of known to be defective, repaired. Most of us "repair by substitution" when these trip computer problems come up.

Years ago there was a guy name Duncan on Jag-lovers. He was a real electronics whiz bang and had a webpage with all the details on the trip computer circuits, etc. if you're interested in the hard core detais

Go to our "Series I-II-III" section and track down Jose. I think he has the info on Duncan's webpage.

Cheers
DD

 

Hell, just knowing there's a fuel interface module is great! I'll look more into it. If it's bad I've still got a parts car. Thanks Doug!

 

Just googled it, I know exactly what it is. I think I even have a spare lying around here somewhere in a box. Was wondering what that thing was.

 

Where is it, what does it look like? My car is the same age and I have no idea at all! Thanks
Greg

 

It's the black box with 4 prongs sticking out of the bottom that has a red sticker on it that says "V.12" and some other numbers. See this ebay ad for a pic:
Jaguar XJS Fuel Interface Relay Module DAC 2589 | eBay

I think this is in the boot somewhere, I haven't located it yet but I recognized it immediately because I have one or two sitting in a spare parts box that i was wondering what they are.

D

 

Thanks Darel. It is on the RHS of the boot, behind the plastic cover attached to the carpet that is just below and to the right of the RHS hinge.
pic here



I had always thought it was something to do with the injection system! Just shows what you do not know. Always something to learn on these cars.

Greg