Jaguar Repair: RIGHYT FUEL TANK BOILS OVER, air flow meter, airflow meter

Question
HOWARD:
THE RIGHT SIDE OF THE 1987 JAGUAR (WITH TWO TANKS) BOILS OVER
WHEN I FILL THE TANKS.I LET IT IDLE JUST TO SEE WHAT WOULD TAKE
PLACE SURE ENOUGH WITH THE CHANGE OVER SWITCH ON THE RIGHT I
BEGAN TO SEE FUEL ESCAPE FROM THE GAS CAP. I TOOK THE CAP OFF
AND LOW AND BEHOLD THE FUEL WAS BUBBLING WITH EXCESS PRESSURE
FORCING THE FUEL OUT THE CAP.WHEN I STOP THE CAR THEN WAITED AWHILE THE FUEL AND PRESSURE DID COOL DOWN AND NO SPILLAGE.
CAN YOU TELL ME HOW TO CLEAN THE UNIT THAT HAS 2 HOSES RUNNING
FROM TANK TO TANK LOCATED AT TOP OF TRUNK THE UNIT WHERE THE LID
CLOSES.

Answer
Hi Richard,

The switching valve is not working. That is the valve that connects both tanks to the fuel supply. When you turn the right tank on, the switching valve receives power and that is suppose to energize the valve and open the fuel supply from the right tank. In your case that valve is either not receiving power or the valve is stuck or failed.

To test the system turn on the ignition switch to ignition (not start) and remove the air filter from the air flow meter and reach into the front of the airflow meter and open the flap and put a screwdriver or anything that will keep the flap open a little. Go to the trunk and disconnect the power wire to the switching valve and then touch the two wire ends together several times and you should hear the valve "click" each time. If it does not "click" test the wire on the harness side for power with a test light or voltmeter to see if it is powered. If you get no "click" and you do have power, you either have lost the ground connection on the valve or the valve has failed.

Even if the valve has failed, you should be able to operate the car on the left tank. The left tank is the "fail-safe" mode because if there is any failure in either of the return valves or the switching valve the left tank will always operate. The only exception to this is if any valve sticks.

Howard