Fuel tank system plumbed the wrong way
 

I replaced the pump in my 1987 XJ6. The car had been sitting in its previous owner's yard for over a year. There was crud in the gas. The crud ruined the used fuel pump he had installed. I did not want that to happen to the new pump. So I put a small filter on each hose from the tanks going to what I presume is a T valve. One line goes in one side. One line goes in the other side. The output (middle leg) of the T valve goes to the intake on the pump. The output goes to a multiport fitting and then to the main fuel filter. There appears to be a return line going back from the multiport fitting to the right-hand tank.

The fuel seems to flow OK with the selector switch pushed in. But with it in the out position, the right fuel tank overflows from the fill point. Can someone start me in the right direction toward a solution? I will be happy to describe this in more detail, or post photos (if that is allowed) and then do what I am requested to troubleshoot the system.

Thanks for your help.

Neal Lewis

The engine does not consume all of the fuel delivered by the fuel pump: there is an electrically operated return solenoid for each tank which works in conjuction with the switching valve in the trunk. All three of these valves are powered through the fuel changeover switch on the dash.

The first step is to verify that the fuel switching valve in the trunk is operating correctly, and this is pretty easy to do. If the filters you installed are clear plastic, you can watch them. Otherwise, switch the dash switch to left tank and clamp the supply hose from the left tank shut. If the car continues to run, you are drawing fuel from the right tank through a switching valve that is not properly sealing internally. Test in both dash switch positions.

If the supply side is not at fault, the return side is. When both tanks are filled, a return solenoid staying in the open position will cause that tank to overfill when you are running on the other one. So you are drawing fuel from the left, and returning to both...or to just the right, if the left return solenoid is staying closed.

The return solenoids are in the rear or the rear wheel arches. Pull the rear wheels, remove the covers for access and test the valves. One or both will be faulty.

Hello,
Read your reply, I have a similar issue with a 79XJ6. Is there a selenoid in the wheel well behind each tire on the Series III? I located one wire that I thought to be for the fuel level indicator but I have not removed the rear quarter panel. Is it necessary to do so? There doesnt appear to be any screws to remove an acces hatch in the rear wheel well. Here is my recent post with the historical details of my efforts.
Thjanks for any help you can offer.
I am having a fuel management issue with a 1979 Series III XJ6. with 70K actual miles.
We haven’t driven it regularly several years but maintained it a casual use driver.

The problem:
The fuel gage indicates the right tank is full, in fact it is pegged past full, however the tank if not empty is pumping the fuel to the left tank. Depending on the amount of fuel in the tank the car will stall in a few minutes as the tank is emptied into the left tank and the engine is starved. When the dishoard switch is pushed to indicate the left tank, the fuel gage indicates the left tank is empty however the tank depending on the amount of fuel in the right tank fills with the contents of the right tank which is pumped until dry. This initially seemed like a simple enough problem if I ignore the gage.

The attempted repair:

1. The fuel pump works, the fuel rail is pressurized and the engine runs normally.

2. Even after checking and determining that the change over valve (CAC8000 CAC 3941) seemed to be working properly switching back and forth when powered and then static without power. I replaced it anyway. The condition of course was the same.

3. The next logical component after looking at the service manual to me, was the non return valve.(CAC2027) no test was available so it to was replaced without success.

4. The fuel line was disconnected from the changeover valve and the engine ran normally on the right tank. When powered by the switch with the valve worked normally with the left tank.

5. The dashboard switch is switching from right to left by supplying power to the crossover switch.

I have been reluctant to remove the fuel level sensors and I have not been able to determine the location of the air bleed vale nor do I know is this could be part of the problem.

Since I have owned this Red Cat more than 25 years, I own all of the associated service and parts manuals. I believe and have reviewed the associated trouble shooting procedures. I want to believe this is not an electrical issue but, have yet to rule out the prince of darkness because the valve and pump seem to be working normally and logic says that the condition I am describing is not possible. The gage however should not peg full on the wrong tank anyone have any ideas?