Hey there,

I am experiencing a fuel system issue in my series III xj6. Just a note, I have read many of the helpful troubleshooting guides for common fuel system issues is the Series III xj6, but I must be missing something.

I experienced what I thought was the all too common tank overflow issue seen on the SIII xj6 when one of the valves fail or there is an electrical/switch issue. Let me describe how I have troubleshot the issue and maybe there is some help out there on what I am missing.

Backstory: RH tank overflowed one day, I was uncertain of the tank that was selected at the time. When it happened, I had the day prior filled up both tanks. As the RH tank overflowed, I switched between the tanks and could see one was full (RH Tank), the other was empty (LH Tank) and fuel was blowing out the RH cap on the freeway.

I get the car towed home and look up the issues with the fuel system (Forums) and decide to purchase the RH tank fuel return solenoid as I thought I was on the LH Fuel Tank when the issue arose. Once the part arrived, I began the troubleshooting process. First, with a 12V test light, I check all three valves. When RH tank selected, all three valves have voltage. LH tank selected, no voltage as it should be. Second, I have my wife push in and out the dash switch to hear that all three valves were clunking and switching back and forth. At this point, I replace the RH tank valve since I already purchased although there seemed to be no issues here. Third, I siphon 3 gallons of fuel out of the RH tank and place into the left.

Fourth, I start the car and it runs again (previously died on the freeway). I select the LH tank and can hear the return fuel flowing in as appropriate into LH tank and do not hear the fuel flowing into the RH tank. All is good. I repeat with the RH tank, again, all is good. I let the care idle with occasional revving for about 15 minutes occasionally switching tanks. Again, no issues. Fuel gauge is holding strong on both tanks. I think it must have been a fluke event.

Fifth, I decide to move the car in the driveway. No extra throttle just moving back and forth a couple feet to get it closer to one side of the driveway. In this short process, I see the RH tank fill up (the selected tank) and the LH tank empty. Shut the car off, indeed, RH tank is overflowing again.

What could cause the fuel to move to the other tank only once the car is in drive? How is gas still coming over? Should I replace all 3 valves just in case, or is there another thing I am missing?

Thank you all for the help!

 

Feeding from on e tank and returning fuel to the other...

 

As you can hear the fuel returning to the correct tank with the selector switch in each position, it must be drawing from only the left tank. So I think the changeover valve in the boot that chooses which tank to draw fuel from must be stuck in the position where it only draws from the left tank.