QuestionHello Howard I have a 1985 Xj6 that starts to spudder when it gets to running temp. I can't find a reason why so I start to check the fuel system I go to open my right tank and fuel sprays everywhere( I don't use this tank normally because the gauge don't work) but I had hit the dash switch a time or two. I'm stuck and would love the help. Thank you!
AnswerHi Brandon,
The fuel system has three valves, a switching valve in the trunk that selects which tank to draw fuel from. When you select the right tank the switching valve is powered and when you select the Left tank no power is applied to the valve and it is spring loaded to the left tank.
There are two return valves located under a panel at the bottom of each rear wheel well. When you select the tight tank the fuel switching valve is powered and opens the right tank to the fuel pump and the fuel is pumped forward to the injection system under pressure but the injection system can not use all the fuel pumped forward so a pressure regulator bleeds off most of the fuel and sends it to a unit near the AC compressor to be cooled and sent back to the same tank that is selected. When that is the Right tank it powers the right return valve to open and powers the left return valve to close. Thus the fuel returns only to the Right tank.
When the Left tank is selected the power is turned off to all three valves and since the switching valve is spring loaded to the Left tank only fuel is pumped from the Left tank. The Right return valve is spring loaded to the Closed position so no fuel can return to the Right tank and since no power is supplied to the Left return valve and it is spring loaded to the Open position fuel can only be returned to the Left tank.
To test the system, have someone turn on the Ignition (not start) and select the Right tank while you have your finger on the switching valve in the trunk. You should feel it "Click". Also test the power wire for 12v at that time and test the ground wire to be a good ground. Then turn the key off.
Then if it works correctly remove the air filter can and place something in the front of the air flow meter to hold the flap door open a little (a screw driver will work) then open the Right filler cap and with a flash light (not a drop light) look into the filler cap while someone turns on the key to Ignition (not start). You should see fuel entering the tank. Then look in the Left filler cap and you should not see any fuel returning to the Left tank.
Now have someone switch to the Left tank and check that no power is on the power wire at the switching valve and look into the Left filler tank and you should see fuel returning to the Left tank but not the right tank.
The system was designed like this so no matter what kind of electrical failure in the system happened, you could always operate off of the left tank. Other then a stuck valve if you select the Right tank and it over flows the filler cap, most likely have lost power to the right return valve or it has died.
You may need to print this out to follow it at the car.
Howard
