QuestionQUESTION: Hello I have a 1984 xj6 series 3 the car sat for 8 yr. put new Battery and coil car stared and runs good has leak in L tank noticed it after running out of gas changed over to R tank put gas in it only held a Gl. or 2 tank was full of old gas but i had to get home gage on dash read full car stop half way changed back to L side put in a Gl. from gas can mad it home ok drained R tank put on new filter 5 Gl. gas in car will not run on L tank dash gage has not moved also did the light in the tank test should fuel return in spurts or should it be running out the return lines it comes out in spurts on my car both sides will not run on R side. please help if you can thanks.
ANSWER: Hi Jay,
The tank switching system has three valves. A fuel supply valve in the bottom of the trunk that is open normally to the left tank and only electrically switched to the right tank.
The other two valves are located at the bottom of each wheel well under a metal plate. These are the return valves and the right valve is normally closed and only electrically opened to return fuel to the right tank
The left return valve is normally open and only closed electrically.
This system allows you to operate on the left tank if any electrical failure happens. This is designed as a fail safe system and that is why you were able to operate on the left tank.
The system can still fail if a valve sticks.
When you have the left tank selected you should only see fuel returning to the left tank and only to the right tank when the right tank is selected. Never both. The amount of fuel returned is controlled by the fuel pump in the trunk and the pressure regulator under the hood
It is very important to test fuel pressure. Running it should be about 32 PSI and vacuum removed from the regulator should be about 42 PSI. If your pressure is low, before you condemn the pump you need to check the fuel filter in the trunk.
The switch on the dash controls the tank switching valve and the return valves and the fuel sending unites.
The sending units are in each tank behind the tail light assembly. After sitting for a long time the arms usually rust and stick. I have been able to save about 50% of the failed ones by removing them and using WD-40 or such and manually moving the arm back and forth a little at a time until you get full travel.
In the case of a leaking tank that is not the drain and filter plug. If you intend to remove the tank and have it repaired (some radiator shops do that kind of work) I advise you to purchase a service manual. Not that it is that difficult to remove but it must be aligned when reinstalled and you just need to know how to align it. A little too much to cover in this program.
Howard
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QUESTION: Hi Howard thanks for your help. I only get fuel returning in the tank that is selected so if fuel is returning on the (R) side but the car will not run on that side or could the back fire and cutoff be that it need to run the bad gas out of the lines when I change switch it click and fuel return in the tank that is selected but it cut out, back fire, then cutoff when the R tank is selected like its out of gas. Could I hear click of the switch and get returning fuel in the selected tank could something be sticking if I put gas in leaking tank (L) it will start without switch at the dash. Thanks again!!!
AnswerI learned a long time ago to forget symptoms and go by my tests only to diagnose a problem.
First test of the fuel system is to confirm fuel pressure (32 PSI running and 42 PSI with vacuum removed from the regulator)
Next open both tank filler caps and with a flash light look to see if the fuel is returned to the tank that is selected ONLY.
You can use the sound of a "Click" of the tank switching valve to see if the electrical solenoid is operating but it does NOT tell you if the valve closed off the one side and opened the other.
You should have drained that bad stale gas out and put in fresh gas anyway. You are running in circles with so many wrong things without correcting any of them.
If you don't want to remove the fuel lines to test the switching valve you can take a fuel line pinch off tool or put two short pieces of rubber hose on a pair of needle nose vice grips and clamp off the left tank line and switch to the right tank and remove the air filter and put a screwdriver in the front of the air flow meter to open the flap a little and turn on the ignition key to "ON" not "Start" and that activates the fuel pump then look in the right filler cap to see if it is pumping fuel. If it is, you at least know it is drawing fuel from the right tank as it should and returning it to the right tank as it should.
Stop trying to guess what is wrong and just run tests.
Howard
