Equalizing tanks - the FAQ

[dr_bgd@thibodaux.com (Dr. Bart Denys)]

Jag-lovers,

Equalizing tanks is not an uncommon occurrance and can be a frustrating
experience. Here's my scope. Maybe Nick can put it up on the tech-list.

Components:

	1.Fuel switchover valve. This 3-way valve is located in the trunk, to
the rear of the spare tire. It is bolted to the trunk floor and has 3
hoses. The left hose goes to the left tank, the right hose to the right
tank, and the central hose to the fuel pump. The solenoid has 2 wires
with bullet connectors that attach to the wire harness in the rear of
the trunk, very close to the remote antenna motor (XJ6-III). Activation
of the solenoid selects either the right or left tank.A normal
functioning valve does not allow fuel to run between tanks.
	2.Fuel return valves. The pressurized fuel returns from the fuel rail
to the rear of the car. The line splits in a T with one arm going to
each tank. In each wheel well there is a fuel return valve.To get to the
valve, remove the rear wheel. Covered with undercoating you will find a
cover either attached to the body with two philips screws or with an
additional bolt (later models). Pry off the undercoating from the screws
and remove. You will now see the valve, attached with two screws to the
body. A large black arrow indicates flow direction. The left and right
valves or mirror images and NOT interchangable. The solenoid wiring goes
into the tank cover and CANNOT be detached from the valve.  Remove the 4
screws from the tank cover and you will find the two bullet
connectors.The valve has two functions. A ball type valve inside
prohibits fuel to flow from the tank towards the return line.When the
solenoid is not activated, fuel can run from the return line into the
tank. When activated, the solenoid prohibits fuel from being returned to
that tank.

Function:

When selecting the right tank, the fuel switchover valve will allow the
fuel pump to access that tank. The RIGHT fuel return valve is not
activated while the LEFT return valve is. This directs returning fuel to
the right tank only.

Where does it go wrong ?

A defect in EACH of the three valves will allow equalization.
	1. Fuel swichover valve. When the valve does not seal well, fuel will
run from te fullest to the lowest tank, usually at a relatively fast
rate (equalization of a full tank in a few hours)
	2. Non return valves. If the INTERNAL BALL VALVE doesn't seal, than
fuel can run from that tank to the other when the car is not running.
Remember, these are one way valves when not activated.So a broken left
sided valve will leak and there is no passive valve on te other side to
prohibit fuel from entering that tank. If the SOLENOID is broken, then
pressurized fuel will be returned to BOTH tanks, again allowing for
equalization.

Trouble shooting.

1. Testing the switchover valve.
When both tanks are empty, fill the left tank half full. Wait overnight
and check. If both tanks equalized, refill the left tank 1/2 to 3/4 and
put a clamp on the fuel hose from the left tank to the swichover valve.
Wait overnight. If no equalization occurred, than the switchover valve
is a culprit. Now the non return valves can be tested indirectly.
2. Testing the RIGHT non return valve.
After completing 1., the left tank is 1/2 - 3/4 full and the right tank
is empty. Remove the clamp from the LEFT fuel hose at the switchover
valve and put it on the RIGHT hose. Select the LEFT tank and drive,
drive, drive. If there is an increasing level in the RIGHT tank then
that non return valve is defective. In some cars, you can actually hear
the solenoids click.
3. testing the LEFT non return valve.
Reverse of 2.

Please note that sofar this is a "white collar", non grease approach to
have a preliminary idea as to where the problem may be. Now were playing
mechanic.

1. Disconnect the bullet connectors of the valve and attach a volt
meter. Push the tank select button and make sure that there is a 12V
reading. Otherwise troubleshoot electrical first. Remove the switchover
valve. Blow through either end. Air should only come out the fuel pump
end. If there is a little leak, you can try to clean the valve with carb
cleaner, although in my experience, this is mostly a temporary solution.
Apply 12V to the solenoid and check operation by blowing through each
end. My advice: if there is the SLIGHTEST leak, call Hal Rogers and get
a new valve for $48.50.
2. Disconnect the bullet connectors of the non return valve and apply a
voltmeter. When selecting the RIGHT tank, the LEFT valve should read
12V. If not, chek electricals first. Repeat for the right valve. If no
electrical problem, remove the non return valves as outlined above. Blow
AGAINST the direction of the black arrow. There should be NO leak. Now
blow in the other end (in the direction of the arrow) and activate the
solenoid by applying 12V. Again there should be an air tight seal. If
not, same advice and another $48.50.When testing these solenoids, DON'T
rely on a clicking noise. Most newer valves are completely quiet. Test
by blowing through the valve and applying 12V.

Alright, you can now again play with the tank select button and enjoy
seeing the fuel meter indicating different levels. Of course, the above
assumes that there is no problem with the tank sender, the fuel meter,
or the electrical system.

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Follow-Ups:

• Re: Equalizing tanks - the FAQ
• From: Randy Wilson <randy@taylor.infi.net>

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