At some point in distant time, my fuel gauge began reading only a little over 3/4 tank when fully filled, and its companion low fuel indicator lamp comes on "early" at say 14-15 gallons burned (20 gallon tank).

I can erase any thought of the instrument cluster being at fault, I think. It has been meticulously cleaned with regard to its connections, and a redundant ground wire attached.

This leaves the sending unit in the tank as prime suspect. Could it have a "lazy" float, maybe loss of buoyancy?

Has anyone else had this problem, and was it related to the sending unit? Is it major brain damage to remove, repair, or replace it? Can it be accessed in the boot?

Thanks again to those who know,

Lou

 

Flakey sending units and leaky floats are both fairly common on these cars as they age.

The sending unit is easy to reach from the trunk....just remove the spare tire and the carpet that covers the tank and there ya go. Make darn sure the fuel level is below the opening though or you'll have a real flood on your hands ! (I sure you know that...but I had to say it).

Some guys have repaired the sending units and found suitable generic replacement floats...worth a try. Might be just dirty contacts on the sending unit resistance wiper.

FWIW, a new sender wasn't very expensive so I opted to just replace it and be done with it when I had problems...but that's me.

Cheers
DD

 

I had the exact same problem with Katie. Cleaned connections and patched the float. Good to go.

 

I have the same issue, so based on this post I think I'll add this to the to do list.

I was happy using the fuel computer, as it's very accurate, but I've been "reseting" things a lot recently by disconnecting the battery, so my fuel computer keeps losing it's memory.

 

That's why I always keep a container of Spare Fuel in my car now.

My fuel gauge doesn't work properly like so many others.

Check it out.

http://www.sparefuel.net

 

I wouldn't doubt that is the problem. When I got my car it has been sitting for 12 years and the unit wouldn't move at all. It seriously only take like 20 seconds to take it out.
I sprayed it with penetrating oil all over and left it for a bit. Then i moved the arm back and forth myself until I was satisfied it was smooth.

you can always check it doesn't hurt, plus it takes no time at all to get that unit out.

 

Same problem over here with the XJ40. I tend to look at miles travelled versus fuel added.

Rocket, just a friendly reminder, but straight out commercial posts are frowned upon and may be deleted as spam.

 

Is the fuel computer driven by something other than the float in the tank ? ...so that it can indeed be relied on ??
Thanks.

 

Do you have to replace sending unit gasket or is it reusable? My car runs out of fuel at 1/4 tank.

 

I agree that for early cars, the fault will very often lie with the float / sender. But for facelift cars, the pessimistic fuel gauge syndrome is far more likely to be the anti-slosh module which are a known failure item

PAul

 

Although I have not done this job (it will wait until the car is laid-up for winter...) but I would suggest that for the cost of a gasket, it would be best to replace it.

I would also suggest that when removing the securing ring etc., that a brass drift be used, or similar, as opposed to a steel one. Steel on steel may produce sparks. Sparks like gasoline vapours. :-)

 

It is a very good idea to replace the gasket. A fuel leak can be a very serious and difficult problem to deal with.
The sender unit is essentially a variable resistor. As the fuel quantity goes down, the resistance goes up. I would guess that units developing higher than normal resistance as they age would be a more common problem than the reverse. That would cause the gauge reading to be lower than the actual quantity. And yours is reading higher than the actual quantity. So the sender may not be your problem.


But replacing the sender is fairly cheap and easy. So it may be worth doing anyway.

 

Hi all. Here we go.

I have just bought a 92 XJS Coupe and obviously my fuel guage is pinned at E with a full tank. After reading all the posts, I figured it was the anti-slosh module, so i made my first of many purchases to clean up some of the issues I can't live with - like not knowing how much fuel I have.

The new one came in today and was in the car in 5 minutes. I assumed I had done the easy fix, but no dice.

Is my next step the sender?

 

First question: Does your car have the small sump tank under the battery, or does it have the later in-tank pump system?
Greg

 

Yip, mine only shows 3/4 on fill up.
When I first got the car tried to top it off and gas started running out from under car, at least a gallon or so, very dangerous. When gas handle clicks off, no more gas added.

 

 

[QUOTE=Ollie2576;1871232]Hi all. Here we go.

I have just bought a 92 XJS Coupe and obviously my fuel guage is pinned at E with a full tank. After reading all the posts, I figured it was the anti-slosh module, so i made my first of many purchases to clean up some of the issues I can't live with - like not knowing how much fuel I have.

The new one came in today and was in the car in 5 minutes. I assumed I had done the easy fix, but no dice.

Is my next step the sender?
= = = = = = = = = = = = = = =

My 92 4L had the same issue a couple of years ago but I changed the sender first. However, I had an inaccurate and temperamental gauge reading and so I had a rough idea of fuel in tha tank. I ran the fuel down to below the access. This was part guesswork. I would not attempt to change the sender if the fuel is above the sender opening. Otherwise the fuel will flood the trunk/boot. However, I changed the sender and all was well. The float on the old sender was completely rotted. I thought briefly about trying to repair the old sender but the gubbins and the resistance “wiper” did not look to be in good shape so I thought “why bother” and opted for the new sender.
Just make sure that you get the proper sender. The first one I was given was not for XJS and the arm was too short, if I remember correctly.
Hope this helps.

 

 

OK, you have the sump tank under the battery. The reason I asked is because the sender on this system is easy to get at and test, as you know it is behind the spare wheel.
Get at it and you will see three wires. The black is the earth wire. The other two are: the gauge level and the low fuel warning light. Ignition on, remove first one and with a friend looking at the dash, touch it to earth quickly (do not hold it to earth). You should see the light come on when one is earthed, and the gauge move when the other is.
If you do, it means the circuits are fine and you need a new sender. If you do not, it means the circuit is bad. So you will have to start testing it, first to see if there is 12 volts at the two wires you earthed, and take it from there.


Greg