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?

 

I had similar trouble with a 1980 XJ6 Series 3, so I assume yours is the same, with fuel injection.

As I recall, there is a switchover valve in the boot to switch the tank the fuel pump draws from. On the return side, there are two valves, one each side at the back of the rear wheel arches, (the return pipe goes to a T-piece from which a pope runs to each valve. Each one works opposite to the other to ensure that fuel drawn from a tank is returned to it, so one valve closes and the other opens. the valves are "handed" so the valve for the LH side is not interchangeable with that for the RH side. All of this is switched by the single changeover switch on the dash.

As a little "I've been there" story, I was once coming out of Burford, England, going north returning from holiday with car boot full, back seat full, plus 2 year old daughter in her little seat; the hill out of Burford goes on for ever, and I noticed the tank was running low, so switched to the other, only for the car to die from lack of fuel. I quickly switched back and managed to turn into a side park area (= "layby" in England). Emptied out the WHOLE boot, then managed to get into the spare wheel compartment, out with the wheel to take off the cover to get at the valve, and a little tap with a spanner and over she went to the other tank !!

The thinks we put up with in those days !!

 

Thanks to Doug Dwyer, I was able to follow his procedures and rest assured (much to my surprise) the problem does not appear to be electrical. Everything points to a faulty valve (electro – mechanical) or valves . Neither seems to operate consistently and both are very rusty. The covering shields were deteriorated and moisture apparently found a home. I plan to order both ( OEM parts) and hope to have them by next weekend for installation. The shields seemed a good idea to keep the moisture away from the valves, unlike my first MGB (new in 1966 with positive ground). Every time it rained it would stall after going through any kind of small puddle. After a little investigation, I discovered the folks at British Leyland had located the electric fuel pump right behind the rear wheel. Silicone spray was my shied of choice at the time.
Kenn

 

The two fuel transfer solenoids arrived on Friday and were installed behind each wheel yesterday. One of the replaced units after being removed seemed to be intermittent in operation and the other seemed to allow only partial flow. Both of the units were extremely corroded on the outside.
With the new solenoids in place all electrical tests were performed and indicated normal operation but alas the symptoms remain. I have read and reread the Service Manual and studied the electrical schematic. The schematic seems straight forward, when the dashboard switch is pressed the guage indicates a switch of the tanks. Unfortunately the fuel gage indicates full (immediately to the full peg) on the left tank when it in fact being drained until empty) and when switched, the right tank indicates empty (to the empty peg) although it is being filled), I couldn’t find any reference for testing the tank sending units or any specifications to measure the accuracy of the sending unit in the Service Manual. I have not removed the dash-mounted transfer switch it seems to be functioning normally. In review the Fuel pump is working the three solenoids have been replaced the backflow valve has been replaced the service test for the solenoids indicate they are functioning normally. Any ideas as to what tests should be done next ? I would welcome any recommendation for someone near Woodstock, Illinois that has the necessary skills to help diagnose and repair this red cat.
Regards