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Jaguar Repair/fuel crossover


QUESTION: Hello Howard,
Thank you for your help with my fuel senders,the gauges now work perfectly.Problems now i am encountering in an attempt to get this car saftied , with a leak at the left tank.And with this leaking i realize that the 1/2 full left tank has dumped it's contents to the right side tank.I have found the changeover valve as Faulty,I am now trying to locate the crossover valves.They must be under the tanks but there is alot of body work to remove.Please tell me they are more easily accessable.
I appreciate your help again Howard
Regards Paul

ANSWER: Hi Paul,

No, the return switching valves are easy to access. Just remove the wheel and you can see a removable plate at the lower edge of the fender well a little to rear of center.

The way the system works is that when you select the left tank all power is shut off to the tank switching valve in bottom of the trunk spare wheel well and to BOTH return valves. The left return valve when turned off electrically is open to return fuel to the left tank. The right return valve when turned off closes. At the same time, power is turned off to the tank fuel supply switching valve which is spring loaded to the open position for the left tank to supply fuel to the engine.

When you select the right tank the fuel supply switching valve receives power and it's solenoid closes the left tank and opens the right tank. BOTH return valves receive power and the solenoid of the left tank closes and the solenoid of the right return valve opens to return fuel to the right tank.

The reason they do it this way is so that if there is any electrical failure in the system, you can operate off of the left tank because all three valves are designed to have the left tank operating with no power to any valve. The only problem with the system is when any valve sticks in the wrong position when power is turned off.

The two return valves look alike but they operate in reverse of each other.

If you have selected the left tank and it is returning fuel to the right tank you have one or more problems. For sure the right return valve (at the bottom edge of the wheel well) is either stuck open or a "left" valve has been installed on the right side.

Here is the test procedure. Key on and select the right tank and open both caps and take a flashlight and a screwdriver and open the flap valve in the right filler cap and look down into filler neck to see the fuel returning to that tank. Now look in the left filler neck and you should see "NO" fuel returning to the left tank. Now, select the left tank and look into both filler necks. You should see fuel returning to the left tank and when you look into the right tank you should see "NO" fuel returning to the right tank.

If when you select the left tank and you see fuel returning to both tanks then the right return valve is stuck open or it it a left return valve.

You should also test for power at all three valves when the right tank is selected, and test to see there is "NO" power at any of the three valves when the left tank is selected.

Let me know what you find.


---------- FOLLOW-UP ----------

QUESTION: thanks Howard,i misunderstood all of the other threads.i was looking under neath the spare tire.
Could you tell me what the metal lines are that surround the access to the return valves are ?
Thanks again

Hi Paul,

I don't know of any other metal lines in that area other then the fuel return line. I don't remember the routing of the return line from the valve back up to the filler neck where it enters the tank. It might make a loop and go back past the valve and forward and then up to the filler neck. It has been too many years since I had one out. That is the only thing I can think it can be because there are no brake lines in that area and the fuel feed lines are very large and short inside the trunk.


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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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