The fuel gauge on my '90 XJS always reads empty. I have done the following;

1. Removed instrument cluster and cleaned all contacts.
2. Replace the fuel sending unit.
3. Cleaned all of the grounds located in the trunk (The fuel gauge ground is there)
4. As a test I grounded the Light Green/Orange wire. The gauge would read Full.

As a test I want to put a resistor in the feed line to see if the gauge will indicate Half-tank but I don't know what resistance I need.

Does anyone know the resistance range of the fuel sending unit?

If anyone has any other troubleshooting ideas please let me know.

Thank you!

mark

 

Have you got the barrel gauges or the round ones?

 

My 95 sender varies between 16 - 250 ohm empty..
Not sure if your has a slosh module but I understand they are prone to failure and flaky readings.

 

My XJS has the barrel gauges and does not have a slosh module.

 

I've got the opposite problem in that mine is always reading full {lovely idea but I don't think it will drive very far!}.
It was ok until I pulled the instrument panel to change bulbs and Speedo.
Constant faffing about in the restricted space caused a bit of damage to the circuit ribbon at the back including live and earth tracks coming into contact with each other which hopefully I have sorted (find out in couple of days).
Another thing that I had done was bend the temperature gauge needle enough for it to press against the gauge and not move.
Might be worth a look.

 

ughhhhh, I lost the sheet. man, that was my only printout too...

I think it is around 20-200ohms, but I am not entirely positive.

From my personal experience the sender is usually fine and the wiring from the sender is usually fine. Generally the issue is with the connector and primarily the weird flexible printed circuit that goes on the instrument cluster. Cleaning that up helped mine a lot, but it is still not great.

One day I am just going to put wires on the whole instrument cluster and throw away the stupid thing

 

I nearly did it, but in the end made the blue thing work, but I 100% agree it would be the best thing to do. Also, you can make the wires long enough to easily pull out the cluster and install, à la Brahe Buster, decent modern multiplug connectors. In my case anyway, a great deal of trouble is caused by the big OEM cluster plugs having not enough free length to pull them out of replace them in the cluster easily without wrenching something important out of true contact.

Greg

 

Mark
If grounding the wire makes the gauge move, it is not the cluster, or the wiring. If grounding the low fuel light wire lights the warning light, ditto.

The odds are the sender is shot. If you pull it out (CAREFUL of fumes being lit by sparks, close off the hole with something) and wiggle the sender vigorously, you may, repeat may, get some gauge flickering. FWIW, I think you are looking at a new sender, this pretty much repeats my experience.
Greg

 

Hi Greg,

I agree with your diagnoses and had the same thoughts so I ordered and installed a new sender but the gauge still will not respond.

What I want to do this weekend is pull out the cluster again and apply an input directly to the gauge. I will use a 100 ohm resistor and see if the gauge will indicate something in the middle of the range.

Stay tuned.

Mark

 

Mark, does the warning light work when the sender is at the bottom of its travel? if not does it work when earthed direct from the sender wire (like the gauge did). If it works directly earthed and not via the sender, then it might be worth running a new earth from the sender and re-checking before pulling the cluster. The earth wire from the sender might be broken/not earthing properly.

Greg

 

You are sure you have it wired properly? Like greg said, check the ground. I think it runs off near the battery somewhere.

 

1996 Vanden Plas. Fuel gauge shows only 3/4 full when tank is full and at the next start shows only 1/4 full. All of a sudden it will show full and revert back. Would replacing a sending unit help? Any pictures or video how to replace?

I keep track of the odometer mileage and my car gives about 18 miles to the gallon. I am able to assess the gas level in tank, but would love to have this fixed. Thanks for any help.

 

Well, I finally figured out the problem and the fuel gauge is now working.

I checked all of the wires and the instrument cluster and everything was fine but I just was not seeing a signal from the sending unit. I finally decided to test the new sending unit and found that it was not working!

Like most people I just assumed that a brand new part out of the box would work properly so I did not bother to test it before I installed it into the tank. Once I tested it and found no resistance I knew that had to be the problem.

I decided to restore my old unit and swap it out for the new one. Now the sending unit has resistance and the gauge works properly. I didn't have time to find the fault with the new sender but I will look at it soon, fix it and add it to my parts bin.

BTW, the sending unit ranges from approximately 20 to 220 ohms.

Mark

 

A 470 ohm resistor should get you a 1/2 full reading if all is good.
Are you sure that your car does not have an anti slosh module? If you do that can fix the problem.
Good luck!
Jomo

 

No anti slosh modules on any pre-facelifts, AFAIK.

Greg

 

Hi Jomo,

As you can see from my post above the range of the sending unit is 20 to 220 ohms so a 470 ohm resistor would be too much. Also, as Greg mentioned, the Anti Slosh relay was not used on the pre-facelift cars.

As I was looking through my box of resistors I came across a 68 ohm. It would show about a 1/4 tank. Once I saw that I knew that my wiring and gauge were working but the sending unit was not.

Replacing the sending unit (again) resolved the problem.

In a way it was good because it gave me an excuse to clean all of my grounds and do a restoration on the instrument cluster. Now everything is working perfectly.

Mark