Hi, we just bought this Green beauty last Monday. Drove it home about 250 miles and all went well. I filled up the fuel tank three days ago and last night on our way home the gauge started dropping fast. This morning, it was on empty and the fuel light is on. I'm quite sure it is still nearly a full tank as it's only been driven about 25 miles and no sign of a leak. I checked around this forum and found a wiring diagram and traced the wiring to the fuel sending unit. I'm getting battery voltage at the sending unit on the B/W wire. If I ground this wire, the gauge should read full shouldn't it? I should tell you, I'm a fleet mechanic and have about 25 years experience on many different types of equipment, however, this is my first Jag.
Thanks for being here, I found the wiring diagram in about 10 minutes and it was quite helpful.

 

New development, this morning gauge was back up near full again. On the way to town, about 3 miles in, started dropping again. By mile 7 it was on e again. I believe we have some corrosion in a connector causing resistance to go up as the wire heats up from the high resistance in a corroded connection. A vicious circle for sure. Where is the connection for the shunt circuit to the fuel module? The connector at the fuel sender is clean, I hope the rest of the connects are somewhat easy to get to.

 

Hi, it is a known problem with XJ 40 and 300.
You can test your gauge as the procedure here :
05-1-13e (05-1-13 Incorrect Fuel Gauge Reading.pdf) - Fichier PDF

If you find it too long, you can have a new one, it is not very expensive and easy to change via the loggage case.

If you change it, think to change the ring : ARA1502J
and the fuel sender unit : DCB6936



This is your fuel tank, the gauge is on the front part.
Think to do it when it is empty
Enjoy.

 

Great information.
However, I'm pretty sure it's not the sending unit. Tonight I removed the plug from the back of the dash module and cleaned the terminals with electrical cleaner. Upon plugging it back in, went right to 1/2 tank. Left it idling for a few minutes and it steadily dropped back to empty. I can see some icky stuff on some of the pins in the dash module. I'm thinking of pulling the dash and cleaning everything. Will figure it out sooner or later.
FWIW, the part # you gave for a sending unit brings up nothing in the Jaguar parts search.
I appreciate your time and efforts.

 

Ok. I have the sale thing on my 300. I'll try to change my sender unit ....

Worry for the part number the good one is DBC12042

Part no. DBC12042 | .Fuel tank sender unit Parts From Jaguar Classic Parts AU

 

Well, I've finally decided to go ahead and replace the sending unit. With shipping it only cost $50 and it never hurts to have a new part at that low cost. It appears to only require removal of the spare tire and carpet/panel to access the sender. Will the sender come out of the tank ok without removing tank from car? Previous owner thinks the tank must be removed but with all the room around it, I can't see why. Anybody have any experience with this issue, please chime in.
Thanks for all the help so far.

 

I think it's fixed. New sending unit went in without a hitch. Testing the new unit, full, 3 /4, 1/2 and empty were all shown on the dash. Woohoo! Only took about 15 minutes to swap the unit.