Last week I visited an old friend and had to fill up the tank. But after having driven almost two hours, the gauge still shows full tank...

Don't get me wrong, I do like to always have full tank, but unfortunately that isn't the case... :-(

My firs thought was to disconnect the cables on the tank, but that didn't help, then I sprayed all the connectors I could find and that didn't help either.

Now I'm thinking, could the gauge be stuck in the top position, due to have been topped up too much?

The dash needle movement up to full tank seems to be the normal speed, i.e. somewhat hesitant.

Any thoughts, anyone?

 

I've heard that a bottle of fuel system cleaner added to a full tank MIGHT help free up the stuck float, worth a try maybe?

good luck!

Larry

 

We had this happen with Champ,when we first got her.

Ten minutes,and 30 bucks later,new sender installed,no problem since.

This is apparently one of the problems with these cars,the sender uses a "wiper" along a "board" to give a resistance reading to the dash.

When I inspected the old unit,the "board" was worn through,and the float arm was very loose in it's bushing.

Quite sticky! Easy fix tho,

unplug the wires on the tank,sharp rap on the dash,should unstick the needle on the guage.

Give it a try,Cheers,Jim.

 

Many thanks to both of you!

I've got a bottle of fuel cleaner at home. I'll pour it in tomorrow. :-)

@manwich66
Could you please explain what a "sender" is? I'm not familiar with that...
Then, what would a tap on the dash do? I don't think the needle is stuck, but the floater in the fuel tank.
When turning on the ignition, the needle is slowly moving to full tank... Shouldn't the needle be stuck on full even with the ignition off, if the needle is physically stuck?

 

Correct! come to think of it,if the dash were stuck that would be the case!

Have you pulled the spare,and carpet/board to look at the sender ring?

The round thing on the middle of the tank with the wires is the sender.

Pull the wires from the sender and look for chaffing,a short to ground back there will cause a bad reading.
This was one of the first little jobs to do when we got the Champ car.

Fix the wires,siphon the tank,fit new sender,all good since!

Let us know how she goes,Cheers,Jim.

 

Hi Roland,

I believe the fuel gauge needle is electronically dampened so that it moves slowly to the position reflected by the resistance of the sender. The dampening is to prevent the needle from bouncing around as the fuel sloshes in the tank while driving.

The sender is a variable resistor with a float attached to a moving arm. As the float raises or lowers with fuel level, the arm moves and changes the position of the wiper on the resistance track, which changes the signal sent to the gauge.

As Jim mentioned, the sender is mounted on the rear surface of the fuel tank and is accessible behind the spare tire, jack, and carpeted trim panel. If you have an ohmmeter, you can disconnect the electrical connector and measure the resistance of the sender. Then drive the car for a day or two and measure the resistance again. If it hasn't changed, the sender is stuck. If the resistance has changed significantly, the problem is elsewhere, perhaps an open circuit or short in the wiring as Jim described.

To change the sensor, the fuel level only needs to be a little below half a tank, but since you don't know what your fuel level is, you would be well advised to siphon out as much as you can (which will still leave a few gallons in the tank due to baffles inside the tank that prevent the siphon tube from getting all the way to the bottom).

Cheers,

Don

 

Ahhh, many thanks guys!!! Yes, disconnecting the wires on the sender and spraying connectors, was the first thing I did and because the problem started after having filled up the tank to maximum, I think it's logical to assume, that's the problem.

I'll add the cleaner fluid today and see what happens and if that doesn't do the trick, I'll measure the resistance next and then I think I'll try to see what happens if I top up the tank once more to see if that can get the sender arm to come unstuck again and if that doesn't help I'll take out the sender... Do I need a new gasket for that?

 

Hi Roland,

Yes, the gasket is Part 15 in the diagram below, and Jaguar calls it the "sealing ring." As I recall, it's a fiber or paper gasket, but I may be wrong.





Here's the page where I grabbed the diagram:

Fuel Tank-From (V)629286 - Parts For XJ6 (2.9, 3.2, 3.6, 4.0) from (V)500001 to (V)667828 | Jaguar Heritage Parts UK


To remove the sender, use a bronze drift punch or wooden dowel and a light hammer or mallet to tap the lugs on the locking ring, Part 14. Give each lug a few taps at a time to cause the ring to rotate counter-clockwise, working your way around all the lugs. Eventually the ring will be loose enough to turn by hand and remove, along with the sender and old gasket.

Since your VIN is after 629286, I believe it will have the fuel pump mounted inside the tank as in the diagram. Take care when installing the new sender to not snag the wire rod or float on the fuel pump canister, Part 2, its mount, Part 7, or its hoses, Parts 3 and 4. If the float or rod gets caught on one of those parts, the sender won't operate and you'll have to do the job all over again. This happened to one of our members not long ago.

Cheers,

Don

 

Hmmm, what happened to my reply???

Anyhow...

I did add the fuel cleaner and then I filled up the tank to maximum again. Since then I've driven for over an hour, with the needle firmly stuck on full...

When the level has dropped to under a 1/4, I'll take out the sender and see whats wrong with it...

 

Today something strange occured...
As I was driving, the fuel gauge suddenly went down to the correct level (1/2 tank) and I thought the problem was solved...

But after a short stop at the shopping center, the needle was back on full tank again... which tells me the problem lies elsewhere than a stuck sender arm... since I haven't filled up the tank...

Could it still be the sender, or should I look elsewhere... I'm running out of ideas...

 

It's possible that the problem is the resistive element and wiper of the sender not providing the correct resistance, not that the arm is physically stuck. You can test for that with an ohmmeter as previously mentioned.

 

Many thanks!!! I'll do that.

 

Haven't been driving much the last few days, but have noticed the needle now hovers mostly around the 3/4 mark, although the real level should be around 1/2.

Tomorrow I'll make use of my Ohm meter if the reading is any different than the 112.8 Ohm last week...

 

Now I've got 189 Ohm, but with the needle still at 2/3.

So it seems the resistance is changing normally, but the needle doesn't seem to correspond accordingly...

Ideas???

 

Hi Roland,

Somewhere in the Jaguar literature is a resistance range for the fuel level sensor. The first document that came up in a google search is for the 2002 X308. Page 4 states that the resistance will vary between 15 ohms at empty and 160 ohms when full:

http://www.jagrepair.com/images/TSB/...g%20Issues.pdf


I don't recall how similar those readings may be to the XJ40, but if you do some searching in the literature I think you'll find it.

Cheers,

Don

 

Many thanks Don!

Well the readings on the dash board seem erratic enough... On my car the resistance measurement seems to move in the opposite direction and not being in quite the same range.
But perhaps I should take out the sender for a closer check up...

I'll also see what documents I can find.