87xj6 fuel gauge errors

(Eric Bergman) #1

Fuel gauge only reaches 3/4 when tanks are full, and when first started, needle jiggles somimes at end of travel. Wiring/ connection problem, or sending unit. Repaiable, or replacement?

(Doug Dwyer) #2

Perhaps both. But checking the senders is easy.

Remove the light green wire from the sending unit and, with the key ‘on’, touch it to ground. The gauge needle should swing to ‘Full’. If it does, the sending unit is faulty. If not, the problem is with the gauge or the wiring.

Repeat for the other tank.

Remember to select the appropriate tank with the dashboard switch while testing.

The sending units and wires are easily reached by removing the tail lights…just a few minutes per side.

The above assumes a Series III XJ6. In some parts of the world a “1987” car could be the later XJ40 model, which is quite different


(Eric Bergman) #3

Thank you sir, exactly as you described. Both sending units tested bad, I imagine that a new seal would be provided with the replacement unit.


(Paul M. Novak) #4

Let me add two things to Doug’s response.

The first is to be sure that your fuel tanks are almost empty before you remove the fuel quantity senders. If not you may have a fuel spill. I mention that because other listers have posted about being surprised by dangerous fuel spills when they removed fuel tank drain plugs or fuel quantity senders. Because you sender is faulty you can’t use it to judge how much fuel you have in tge tank.

The second is that the fuel quantity senders have a small float at the end of a long rod that floats on the top of the fuel in the tank. One type of float used looks like a small white barrel. I have found on more than one occasion in my 6 Series III saloons (one XJ12, two XJ6s, and three XJ6 parts cars) that the float was partially filled with fuel and so it wasn’t floating on the surface of the fuel and that was the reason it was giving a low quantity reading. A replacement float with no fuel in it fixed that problem. The later senders have a black plastic float and don’t appear to leak like the white ones could.


(Eric Bergman) #5

Thanks for the extra info, i will make sure to have adequade catch for each 12.6 gal tank prior to replacing the sending units. Speaking of that, it sounds like you made a repair by just replacing the float, but that likely came from another tank of yours, I assume that the float itself is not availible commercially.


(Michael Garcia) #6

…l had one that had never had the previous owner actually fill the tank full of gas for years. When l got it, it didnt register much more than half a tank, after about ten tanks, it registers fine…

(Paul M. Novak) #7

I recommend that you drive your car until you are quite sure that you only have a gallon or two in each tank so that fuel spills are not an issue when you remove the fuel quantity senders.

I don’t believe that the plastic fuel sender floats are available commercially. I was lucky because the first parts car that I purchased was a 1985 XJ6 Vanden Plas and it had the same kind of white plastic barrel shaped floats as my 1984 XJ6 Vanden Plas with the floats partially filled with fuel. My 1986 and 1987 XJ6 parts cars as well as my 1987 XJ6 Vanden Plas had the black plastic floats. Maybe they were aftermarket ones that prior owners already replaced once, or possibly Jaguar changed the design. You will find out when you remove your senders if you have the white floats or the black floats

BTW, I don’t think you can count on a new fuel quantity sender coming with the correct rubber seal (ARA1502J), maybe it will but maybe it won’t. If you purchase a new sender you should ask if it includes the seal. You should make sure you have the new seals on hand because the ones you have in the car might break or tear when you remove them and you want to have the new seals on hand to install them and not have wait for them.


(Aristides Balanos) #8

Ford has Brass floaters that are the correct size.
More info in Kirby’s book.

(Eric Bergman) #9


What is Kirby’s book, how do i see if i want to buy a copy?

(Aristides Balanos) #10

It’s free and you can find it on this site.