Hello everyone!

Something with my fuel tank selection is not working properly. I will have a closer look at it soon again, but if I get some starting help from you until then I might be able to start my work from the right end next time.

This is the situation: The fuel gauge shows empty tanks even though both fuel tanks are half-full. If I push the tank selector button on the instrument panel, a clicking sound is heard by one or more valves in the trunk (probably just from the right return valve by the fuel filter, but I am not sure), but when the button is released valve/s click again and nothing seems to have changed. The tank selector button never “stays” in the inner position as I assume it should to indicate that operational tank has been changed. It always pops back to the outer position.

I can force the fuel gauge to rise slowly by pressing and holding down the tank selector button for a while, but the gauge drops down to zero as soon as I release the button. This makes me believe that one of the fuel tank sender units is faulty, thereby the zero-reading on the fuel gauge. The other fuel sending unit might work as the gauge rises when the button is pressed. If only the button would stay in the inner position, I should be able to see this more easy.

I have read the fuel tank switchover checklist written by Mr. Doug Dwyer and understand that all three valves in the trunk should click (0 or 12V applied on all three at the same time) when the tank selector button is pressed. As I am not sure of how many valves that click at this point, this will be one issue that I will look into as soon as possible. Any other ideas on how to approach this problem?

Just curious: What makes the selector button stay in its inner or outer position? Is it mechanical parts inside the button itself or will the position only change once all three valves are operating properly? This info could be useful to know if the button itself is intact.

 

The switch holds "in" mechanically....some sort of internal latch/ratchet mechanism.

The fuel tank sending unit readings go thru the switch. Since your fuel gauge responds if you hold the switch in I'm guessing the switch itself is faulty....dirty contact or such.

If you're clever, with nimble fingers, you might be able to disassemble the switch, repair the latching mechanism, and clean the contacts. Never tried it myself...but it might be possible.

cheers
DD

 

I am also having a similar problem, however my tank will not switch. I fill up both tanks, but only the right tank works, causing me to run out of gas often, despite the left tank being full, but it won't switch over.

 

Thanks for the replies guys!

I had a look at the switch yesterday and was able to solve the problem without too much effort.

The black plastic button lid was easliy removed (gently pulled straight out) but the actual button was fixed from behind the instrument panel. Instead of unbolting the entire panel, I just tilted the button slightly to the left. With help from a flash light I was able to see the small end of a spring and the "W"-shaped path the spring should run in to be able to stay in the inner and outer position. This was on the buttons right side.

I used a narrow, hooked-shaped tool (more commonly by dentists... it´s the tool that makes every patient scream out loud) and was able to jerk the spring into the path. Thereafter the button stays properly in both in- and out positon.

As the lower plates below the gasoline tanks are removed for the moment, I was able to disconnect the fuel return valves, measure for 12 and 0 volts, and then listening for a clunking sound by the valves when the valves were connected back again at 12 volts. The left valve was completely silent (even though 12 volts were present at the connections) so I will have to change this one soon. Or perhaps it is possible to just clean it? The right valve and the tank selection valve in the trunk worked properly.

The fuel sending unit on the right tank side that doesn´t seem to work for the moment will be dealt with later.

Once again, thanks for all help!

 

Good work





Sure. Worth a try, at least. Perhaps use aerosol carburetor cleaner?

Of course, if the lack of clunk is due to electrical failure there's nothing you can do. As I recall the valves cannot be opened up for repair

Cheers
DD

 

Thanks Doug,

By advice from Frank at the Jag-Lover´s forum, I listened by the filler caps to both fuel tanks and was able to hear the fuel returning to the tanks as it should. So the left valve must have been working fine, even though it was completely silent when switching. Hopefully everything will be fine from here!