[xj] Fuel Changeover Switch

My wife tells me that (on her 89 SIII) occasionally the fuel seems to
travel from one tank to the other. Example: both tanks will be half
full, then suddenly one tank is full and the other nearly empty. Since
this only has been occuring sporadically I haven’t done anything about
it. Yesterday she notcied that theee car stumbled and nearly stalled,
untill she switched tanks.

My question: could it possibly be anything else but the change over
switch? I think not but I could always use other opinions.

-MDF

Well, I have recently been plagued by fuel faults, mainly caused by crud
in one tank. However, the valves have also been playing up.

The way the three valves work is like this.

Changeover valve in boot. Unenergised is directs the flow from the lh
tank to the fuel pump. Energised it directs flow from the rh tank.

Lh return valve (in lh rear wheelarch under a cover). Unenergised it
allows return flow to the lh tank. Energised it shuts flow off.

Rh return valve (in rh rear wheelarch). Unenergised it shuts return
flow off. Energised it allows return flow to the rh tank.

All three valves are wired in parallel. When the selector switch is in,
the valves ar unenergised. Selector switch out puts 12V to the valves.
The return valves in particular are prone to failure, but are not too
expensive (25UKP each). However, if your fault is intermittent, I would
suspect the connections to the wheelarch return valves. The wires run
to a plastic cover plate in the rear of the wheelarch. Inside that they
join to the loom using those daft Lucas connectors. They are prone to
corrosion. So find the wires (you may have to take the metal cover off
the valve), and pull them out gently. They will come out of the cover
plate, and bring with them the hokey connectors. Pull the bullets out
of them, and clean everything up, or splice in decent connectors.

If that doesn’t sort it, tell us exactly what tank fills from which, and
what position the switch is in when it does this. Armed with that we
should be able to figure out what needs replacing.

Craig> -----Original Message-----

From: owner-xj@jag-lovers.org
[mailto:owner-xj@jag-lovers.org]On Behalf
Of Mr. Michael D. Fatsi
Sent: 23 March 1999 15:14
To: XJ Lovers
Subject: [xj] Fuel Changeover Switch

My wife tells me that (on her 89 SIII) occasionally the fuel seems to
travel from one tank to the other. Example: both tanks will be half
full, then suddenly one tank is full and the other nearly empty. Since
this only has been occuring sporadically I haven’t done anything about
it. Yesterday she notcied that theee car stumbled and nearly stalled,
untill she switched tanks.

My question: could it possibly be anything else but the change over
switch? I think not but I could always use other opinions.

-MDF

Craig Sawyers wrote:

Well, I have recently been plagued by fuel faults, mainly caused by crud
in one tank. However, the valves have also been playing up.

The way the three valves work is like this.

Changeover valve in boot. Unenergised is directs the flow from the lh
tank to the fuel pump. Energised it directs flow from the rh tank.

Lh return valve (in lh rear wheelarch under a cover). Unenergised it
allows return flow to the lh tank. Energised it shuts flow off.

Rh return valve (in rh rear wheelarch). Unenergised it shuts return
flow off. Energised it allows return flow to the rh tank.

All three valves are wired in parallel. When the selector switch is in,
the valves ar unenergised. Selector switch out puts 12V to the valves.
The return valves in particular are prone to failure, but are not too
expensive (25UKP each). However, if your fault is intermittent, I would
suspect the connections to the wheelarch return valves. The wires run
to a plastic cover plate in the rear of the wheelarch. Inside that they
join to the loom using those daft Lucas connectors. They are prone to
corrosion. So find the wires (you may have to take the metal cover off
the valve), and pull them out gently. They will come out of the cover
plate, and bring with them the hokey connectors. Pull the bullets out
of them, and clean everything up, or splice in decent connectors.

If that doesn’t sort it, tell us exactly what tank fills from which, and
what position the switch is in when it does this. Armed with that we
should be able to figure out what needs replacing.

Craig

-----Original Message-----
From: owner-xj@jag-lovers.org
[mailto:owner-xj@jag-lovers.org]On Behalf
Of Mr. Michael D. Fatsi
Sent: 23 March 1999 15:14
To: XJ Lovers
Subject: [xj] Fuel Changeover Switch

My wife tells me that (on her 89 SIII) occasionally the fuel seems to
travel from one tank to the other. Example: both tanks will be half
full, then suddenly one tank is full and the other nearly empty. Since
this only has been occuring sporadically I haven’t done anything about
it. Yesterday she notcied that theee car stumbled and nearly stalled,
untill she switched tanks.

My question: could it possibly be anything else but the change over
switch? I think not but I could always use other opinions.

-MDF

OK I think that I have figured out what is happening. With the right
hand fuel tank full, and the switch set to draw fuel from the right tank
the fuel manages to travel to the left tank.

I went to the gas station with two half full tanks. I filled the right
tank to the top and left the left side tank alone. When I started the
car I immediately saw the gauge(which was reading the right side tank)
drop from full to half full. When I switched over to the laft tank it
was full, so the fuel travelled from one side to the other.

Does this mean that my left side return valve is bad?

One other symptom exists as well. When I open the right side fuel cap
there is a very noticable sound of pressure being released, but I think
this allways happened and might be normal.

Thanks for any input!

-MDF

OK I think that I have figured out what is happening. With the right
hand fuel tank full, and the switch set to draw fuel from the
right tank
the fuel manages to travel to the left tank.

I went to the gas station with two half full tanks. I filled the right
tank to the top and left the left side tank alone. When I started the
car I immediately saw the gauge(which was reading the right side tank)
drop from full to half full. When I switched over to the laft tank it
was full, so the fuel travelled from one side to the other.

Does this mean that my left side return valve is bad?

That is exactly what is happening. It may be those Lucas connectors,
but the lh valve seems more prone to failure than the rh one for some
reason. Since it isn’t crazy expensive, I’d replace it anyway. You can
tell where the return flow is going by opening the caps, and using a
long screwdriver to open the flap. If you peer in you will see a tube.
This is the return fuel feed. There should be only fuel returning to
the selected tank, so you can confirm very easily that fuel is going to
the lh tank when the rh one is selected.

One other symptom exists as well. When I open the right side fuel cap
there is a very noticable sound of pressure being released,
but I think
this allways happened and might be normal.

This doesn’t happen on UK cars of '84 vintage, because there is no
vapour recovery carbon canister. I believe that on US cars, a
contaminated canister can cause this build up of tank pressure, but I
have no direct experience here.

Good luck

Craig

I seem to remember lately reading something from a Jaguar bulletin which
said that drawing fuel from the left tank first will reduce the
liklihood of these problems.

Regards Peter Smith

This is one of those ‘‘Stop me before I do something really
stupid’’ posts. The fuel switch on my 80 SIII is badly disfigured
cosmetically. It works fine, but I have decided to change it,
knowingly violating the if it ain/t broke rule. The problem is
access. I can find nothing in the archieve or in Haynes that
suggests how to get to the innards. The switch is in the center
panel just above the radio. There are four screws underneath the
panel and two above. One would assume that by removing these six
screws, one could drop down the entire panel thereby gaining
access. Because this appears to be too easy, I am asking for
verification.

Bruce Hugo–
Bruce Hugo
St. Helens, OR, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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Bruce: you are doing it the hard way. In the early Series III, as in the
Series II, the switch panels on either side of the radio are simply held in
place by four pegs. Gently lever the panel out. Done! Much, MUCH easier than
in the late Series III.
Gregory

: This is one of those ‘‘Stop me before I do something really
: stupid’’ posts. The fuel switch on my 80 SIII is badly disfigured
: cosmetically. It works fine, but I have decided to change it,
: knowingly violating the if it ain/t broke rule. The problem is
: access. I can find nothing in the archieve or in Haynes that
: suggests how to get to the innards. The switch is in the center
: panel just above the radio. There are four screws underneath the
: panel and two above.Subject: [xj] Fuel Changeover Switch

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Hi Guys,
I am replacing my fuel changeover switch. Ordered a new
unit from Coventry West. I removed the switch assembly initially
and it appeared a very small spring was broken, preventing changing
to right tank.
The new unit is a complete assembly that fits into wood
dash panel, but how do I remove the unit? Is it necessary to remove
the whole wood panel to insert the new switch assembly?
Thanks for any advice
Jay–
Jay West 1985 XJ6 1999 XJ8L
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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With some small hands and strong fingers you can avoid removing the panel.
Pull out the trip computer (it wriggles out from the front) and reach in to
wriggle the changeover switch out…after locating the little friction
tabs and squeezing them inwards with your small, strong fingers with
virtually no room to work.

Me? I always end up removing the panel :slight_smile:

The panel is held in by two hidden screws. If you remove the trim panel that
surrounds the radio you’ll see the two screws.

Pull off the climate control knobs and then remove the notched nuts that are
on the control shafts, then gently wriggle the panel away. Be mindful of the
fibre optic cords at the temp control slider. Now you can remove the two
screws and release the wood panel by gently wriggling down and then out.

Lots of wriggling required on Jags :slight_smile:

If you get stuck, shout back

Cheers
Doug Dwyer
Longview Washington USA
1995 XJRFrom: “Jag Jay” jwest87671@aol.com

    I am replacing my fuel changeover switch. Ordered a new

unit from Coventry West. I removed the switch assembly initially
and it appeared a very small spring was broken, preventing changing
to right tank.
The new unit is a complete assembly that fits into wood
dash panel, but how do I remove the unit? Is it necessary to remove
the whole wood panel to insert the new switch assembly?

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: http://www.jag-lovers.org/lists/search.html

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In reply to a message from Doug Dwyer sent Fri 28 Aug 2009:

Thanks Doug! I will give it a try. Hopefully I will not be up
until morning!
Jay–
Jay West 1985 XJ6 1999 XJ8L
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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In reply to a message from Jag Jay sent Fri 28 Aug 2009:

Hey Doug!
Thank you so much for your instructions. Took me about 15
minutes to get the changeover switch in. Works perfectly! ‘’ Mary
Queen of Scots’’ now has both tanks operating and the fuel guage
even works again!
Regards!
Jay–
Jay West 1985 XJ6 1999 XJ8L
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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Good job! That’s fast. It takes me 15 minutes to decide which screwdriver I
like best that day. After that I have to go find my coffee, and then…
:slight_smile:

Cheers
Doug Dwyer
Longview Washington USA
1995 XJRFrom: “Jag Jay” jwest87671@aol.com

Thank you so much for your instructions. Took me about 15
minutes to get the changeover switch in. Works perfectly! ‘’ Mary
Queen of Scots’’ now has both tanks operating and the fuel guage
even works again!

===================================================
The archives and FAQ will answer many queries on the XJ series…
FAQs: http://www.jag-lovers.org/xjlovers/xjfaq/index.html
Archives: http://www.jag-lovers.org/lists/search.html

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