Anyone know how to check a fuel tank change over valve on a bench? There doesn’t seem to be any indication which wire is positive and which is negative.
And how to test the wires in the trunk?
Hi, they are simply a solioid so there is not a power wire and earth so either way will do for the bench test, they do work oppisite however so one will be energized to open and the other will be energized to close.
Hi Frank,
If you connect a voltmeter or test lamp across the two solenoid wires in the trunk, there should be power when the right fuel tank is selected with the ignition on. That’s with the switch in the out position.
regards,
John Hudson
85 XJ6 SIII
Thanks.
I cleaned and Tested the valve it works fine. I haven’t gotten to test the wires yet. Been working on flushing the Fuel lines. The car has been sitting a while. I think the bigger problem was all the orange s*** that came out of the right side tank.
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Whatever the colour, Frank - anything but fuel in the tank is unwelcome…
With power applied to the valve it shoul blow through from the ‘right’ tank valve connection…
Frank
xj6 85 Sov Europe 9UK/NZ)
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There are 3 solenoids that control the fuel flow to and from each tank.
ALL the valves are open to the right tank WITHOUT power. (I think I remember the right tank is open without power?) The default setting for the valve with 3 ports is to the right tank. The right return valve is OPEN without power and the LEFT return valve is CLOSED without power.
When power is applied to ALL the valves they change state (3 port valve pulls fuel from left tank and left return is OPEN, right return is CLOSED)
If this is backward, then the left tank is the default ‘no-power’ tank.
Do not install the return valves on the wrong sides. The return fuel will not flow correctly.
The fuel changeover switch also switches the level senders to the gauge.
bob
03 Fuel System.pdf (2.1 MB)
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To expand and correct, Bob; WITHOUT power; dash switch ‘in’ - the LEFT tank is selected…
Apart from that you are functionally correct. The changeover switch controls two separate electric circuits with separate switch connections; the valve power - and the tank unit via the fuel gauge. Power ‘on/off’ controls two different fuel circuits; tank to pump (changeover switch) - and rail (pressure regulator) to tanks (via return valves). Crux here is that fuel should only return to the selected tank.
The two electrics and the two fuel circuits are independent of each other…
Frank
xj6 85 Sov Europe (UK/NZ)
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Thanks for clarifying. I thought it was the right tank but that’s why I put the disclaimer.
“If this is backward, then the left tank is the default ‘no-power’ tank.”
It has been over 20 years since I regularly worked on these old cars. I forget all that I used to know??
bob