Dear Jag Fan's,

I have recently developed a small (hopefully) problem with my V12 Jag. If I go for a full tank of gas (petrol) my full gage will be on max. he will drop as fuel is consumed. But than suddenly he will completely drop out. now i know its not the floater in the tank. could any one please advise me or does anyone had the same experience and how did they solve it.

Many thanks,

F. Nijen Twilhaar

 

What year is your XJS?

Not sure about the latest models but the earlier cars were simple: fuel tank sending unit, the gauge on the dashboard, and the wiring in between. There's only so much that can go wrong.

Sounds to me like the resistance bar on the sending unit has a dead spot. It isn't difficult to remove the unit for inspection.

Also, the contacts on printed circuit board at the back of the instrument cluster can become corroded and give erratic gauge readings, fairly common XJS issue. Still, though, a sudden drop-out as you've described sounds more like the sending unit in the gas tank.

Here's a quick test: remove the light green/orange wire from the gas tank sending unit. Turn the igntion key "on". Now, touch the wire to a good ground/earth and have a helper watch the gauge. It should swing smoothly up to "full". Now remove the ground and see if the gauge drops smoothly down to "empty". Repeat a couple times. If the gauge responds nicely the problem can only be the sending unit.

Cheers
DD

 

Dear Doug,

Many thanks I will check this as soon as my car comes back from the garage. BTW I have a 1983 V12 XJ-S so your trick should work.

gr. F. Nijen Twilhaar

 

finally been able to check but my meter in the dash stays where it was below broken dash meter??

 

Then A) the dashboard meter is faulty or B) the contacts at the back of the meter are faulty or C) the wiring to the meter is faulty

"A" and "B" are most likely

The instruments often suffer from corroded contacts at the flexible printed circuit at the back of the instrument cluster. The cluster can be removed and the contacts gently cleaned. Adding an extra ground wire is a good idea.

Cheers
DD

 

thank you will check A & B. :-)