QuestionHI HOWARD:
RICHARD AGAIN.
MY 1987 JAGUAR 4.2 LITRE 4 DOOR SADAN RIGHT TANK GIVES ME A HEADACHE..TV'E CHANGE THE SWITCH TWICE THE SAME THING HAPPENS OVER
AND OVER AGAIN...... I SHUT OFF THE LEFT TO SEE IF THE RIGHT TANK
WAS WORKING..IT WORKS BUT WHEN IT GETS DOWN TO THE BOTTOM OF THE
TANK IT BEGAINS TO SPUTTER THEN IT WILL SHUT OFF....THEN I TURN
THE LEFT TANK BACK ON AND IT WILL PULL ALL THE GAS OUT OF THE
LEFT TANK BUT REFUSES TO PULL THE GAS OUT OF THE RIGHT.WHAT IN
THIS WORLD COULD THAT BE?
AnswerHi Richard,
To correct the problem you need to understand how the system operates and how to test it.
There are three valves involved. A switching valve in the trunk that selects which tank to draw fuel from. That switching valve is powered to select fuel from the right tank and when the valve is turned off it is spring loaded to the left tank.
Most of the fuel that is pumped forward to the fuel rail is returned to which ever tank is selected by the switch on the dash. When you select the right tank the two return valves are powered. The right return valve opens allowing fuel to return to the right tank and at the same time the power to the left return valve closes, forcing all return fuel to return to the right tank.
When you select the left tank all power is turned off to all three valves. Since the fuel supply valve in the trunk is spring loaded to the left tank then fuel is pumped from the left tank forward. since the right return valve is only open with power and is spring loaded to the closed position then no fuel can return to the right tank and since the left return valve is only closed with power it is spring loaded to the open position and thus allows the returning fuel to return to the left tank.
The reason Jaguar designed it this way is that no matter which of the three valves fails electrically, you can always operate on the left tank normally. The only exception to this is if a valve sticks in on position.
Here is how to test the system. Remove the air filter and insert a screw driver or any such item into the front of the air flow meter to hold the flap open just a little. Open both gas caps and turn the ignition switch to the "ON" position (not "Start") and select the right tank. Now take a flash light and look in each tank to see if fuel is being returned only to the right tank. Then select the left tank and look in both to confirm that fuel is only being returned to the left tank.
If it is not like that take the lower panels off of each return valve in the wheel wells and open the trunk to gain access to the switching valve. Put your finger on the switching valve and have someone switch it on and off by selecting the right tank and then the left tank and you should feel it "Click". If you don't feel it "Click" test the black wire for a good ground and the power wire for power ONLY in the "Right" tank selection. If there is no "Click" with power on and off you need to remove the valve and test it of the car.
If when you selected the "Right" tank and fuel returned to both tanks, You need to test the left return valve and if you select the "Left" tank and fuel returns to both tanks you need to test the right return valve.
If the fuel returns only to the wrong tank you need to test the wiring and the valves.
let me know,
Howard
