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Jaguar Repair/fuel leaking thru charcoal evaporator


I have a 1986 jaguar xj6 that suddenly begaon to leak fuel right from the charcoal evaporator in the front right wheel well. What caused this and what's the fix ?

Hi Jeff,

The series III XJ-6 uses a charcoal canister behind the right front headlight to capture the fuel vapors from the gas tanks. Just before the canister is a plastic spring loaded valve that maintains 3 PSI pressure on the fuel tanks.

The two tanks are controlled by a switch on the dash which activates a switching valve in the bottom of the wheel well to draw fuel from which ever tank you select. The switch on the dash also controls the gas tank senders to the fuel gauge. That switch also controls the two return valves located at the bottom of each rear wheel well. Most of the fuel pumped forward to the fuel rail is not used by the engine and is routed to the AC compressor to cool the fuel that is rturning to the fuel tank that is selected.

In your case the most likely cause is that either the tank switching valve and / or the return valve has failed and the one tank used is not returning the fuel to the correct tank and has over filled the other tank. When the other tank is over filled the only place for the extra fuel to go is out the vapor line to the canister.

To check to see if this is the case, just open each fuel cap to see if one of the tanks is over full. If it is, then that is what happened.

The only other way this can happen is for you to have filled both tanks to the brim and then the car was left in the sun and thus heated up the cool fuel from underground tanks. Fuel expands a lot when heated even as a liquid and that would force the extra volume of fuel out to the canister.

A simple test of the return valves is to open both fuel tank caps and have someone run the engine and switch to each tank as you use a flashlight to look in the filler neck while using a suitable tool to push open the flap in the filler neck. You can see the excess fuel returning in the filler neck of the tank selected But NOT in the other tank. So when the left tank is selected you should see fuel returning to the left tank filler neck but not the right tank. Then select the right tank and you should see the excess fuel being returned to the right filler neck but not the left.

This ONLY tests the return valves, not the tank switching valve. There is a method of a partial test of the switching valve by going into the spare tire area and place your fingers on the switching valve while someone in the car with the key on, switches the two tanks. You should be able feel the "Click" and possibly hear the "Click". This is not a 100% test of the switching valve but a good sign that it is operating.

Your charcoal canister is now destroyed due to raw fuel in the canister. There use to be activeated charcoal available at auto parts stores but I don't know if you can get it anymore. A new canister may still be available from one of the on line Jaguar parts companies like Engel Imports or Moss Motors. If you are a repair shop it is a federal offence for you to just vent the vapor line to outside air.

Let me know how you do on it.


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Howard M. Fitzcharles III


Jaguar from the XK 120 to XJ-6 ser. 3 1987


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

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Import Car magazine

ASE Master Auto with L-1 certification up to 2000

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