Fuel Tank Return Fuel Mystery

I purchased a 1986 XJ6 a while back. Saw it in an adjoining town just sitting there with a for sale sign on it. Contacted the owner and it was cheaply priced. I bought it as it only had 75,000 miles on the odometer. On the way home I filled both gas tanks because it didn’t have enough gas to drive home. ON the way home I noticed a got a few waves. Did not fully realize why, until I got home and noticed I was trailing gasoline as far as I could see. Did a little reading and figured it was the return solenoids that were responsible. So ordered them. I got one installed on the left drivers side. But then got busy and never got the right one installed until yesterday. Took the cover off and noticed that the solenoid was there and not hooked to any wires!!! Looked for the wires and could not see them ANYWHERE!!! Thus the dilemma!! Where were the wires routed? Can anyone tell me? Surely it did not come from the factory this way or did it??
I could sure use some help from any of you. I guess I could splice onto the wires going to the left solenoid in order to perhaps fix the problem. But will not be original of course. Sure has my curiosity up of why no wires? Did someone remove them and if so why? Can’t see where they might have even come from. The '86 & '87 were wired the same weren’t they? Both return solenoids were wired together isn’t that correct? Please help if you can ~~~
Lee Noga
There is evidence that someone perhaps had the right fuel tank out. I see in the top hole access hole what looks like the wire covering that was normally suppose to be attached to the bottom of the tank. I tried pulling on it but it could not budge it. I was wondering about dropping the tank to see if this is the wire bundle. How much trouble is it to drop the tank? I see one bolt near the top of the tank but cannot figure out what else holds the tank in place. How does one remove the tank? I have the maintenance manual but see no reference to accomplish this task.

Yes, 86 and 87 are the same

I recall, a bit vaguely, that the wires run aft and into a small panel directly in front of the gas tank. From there I suspect they run upwards and join other looms in the boot.

Someone will come along with a better memory


Good to hear from you again Doug. Been a while. I have the shroud
around the gas tank off and looking up & aft of where the
solenoid is, and see nothing. I have a '87 and could compare with
that one but hate to tear it all apart.

Wired together indeed, Lee - all powered or all unpowered…

Have you tried to trace the wires from the connected ‘left’ valve - the other wires may be at the ‘same’ place, opposite side…? And tracing back from the changeover valve, may reveal something…? Any removable panels in the return valve area that may hide something?

Like Doug; I suspect the connections are from the boot area - and removing some panels may reveal something?

That the car left the factory without the connections, and went undetected for years in between, is inconceivable. The return system cannot function without both return valves being electrically powered - some PO machination? To be remedied any which way.

With the valves otherwise functioning as they should (listen at the filler lid), running only on the ‘left’ tank should be perfectly safe - while you are musing. In ‘left’; all valves are unpowered…

xj6 85 Sov Europe (UK/NZ)

Thanks Frank for the message. And yes a real mystery as stated. I
have removed both side panels over the fuel tanks and it told me
nothing. The wire for the one on the left goes up and towards the
front of the auto to be lost. Nothing on the right side. Nothing!!
When looking at the changover valve on the right side it looks like
it has been there forever. And as stated the auto only has 75,000
miles on it. Thus it seems unreal that it would have come from the
factory this way, everything seems to point to this.
I have another mystery with a '42 Packard of mine. It is a business
sedan and they did not make many of them. I had it all
re-upholstered and painted. There was a problem with the left rear
vent window which turned in the wrong way. I did finally find
another cranking mechanism for it but no one makes a vent rubber to
replace the incorrect one. Yes it seems weird that Packard of all
autos would send an auto like this out of it’s assembly line but in
1942 there were very few autos sold because of the war. Attention
was elsewhere and I really think this is the way it came from the
factory. Who would notice the rear window cranking the wrong way for
perhaps a very long time as it was perhaps rarely opened??
Regarding the Jag, what would happen if the right valve was never
hooked up? If the changeover switch was always on the left side
wouldn’t the auto operate okay? Maybe I still don’t know exactly
how this complicated fuel system works.


with a carbed SII car I don’t have any experience with return valves, but your description got me confused anyhow. In all Jaguar series I-III XJ the tanks are completely hidden in the rear wings behind some serious body steel:

You can’t possibly have removed these. Removal of the hardura covers - or whatever was used on late SIII cars won’t reveal much

So I guess that’s why their removal didn’t tell you much.

From the parts catalogue I’d assume the fuel return valve is somewhere underbody and forward of the rear wheels with the solenoid on the right side. IIRC there even was a thread on the valve quite recently. From the parts catalogue it appears though that there is only one solenoid (pt. # 8 in the pic)

As for the wire - I guess one should be sufficient to trigger the valve - I seriously doubt all original owners have been doing on just one tank, even though it would be possible if you were always starting to run on the tank that the fuel return line directed at it. Imagine though the handover talk “And, please, Mr. Doe, never forget to always run the right hand tank empty first, because Mr. Egan, in an attempt to cut costs, decided to omit the wire for the return valve!”

My guess would be it got lost in the heat of action, probably when the tank was worked upon.

Good luck


75 XJ6L 4.2 auto (UK spec)

The whole circuit is powered for the right tank, so with the left tank selected the changeover is passing fuel from the left, the lefthand return is normally open and the righthand normally closed. You could tap off the wire from anywhere on the other two, but I don’t yet know where the wire should be coming from - but I will, this week, as I need to connect my replacement left return valve properly.


David please don’t take offense because I confess I am pretty dumb about
this circuit. But I do know that the solenoid I was going to replace on
the right side is closed with no voltage! Unclear what you are saying.

No problem, Lee: the solenoid for the right tank is normally (with no voltage) closed. As was yours.
The solenoid on the left side is normally open. There is a third solenoid where the fuel pump is, and it selects the feed source. The left tank with no voltage.

All three solenoids operate on the same circuit so if the wire has gone missing altogether you can source power at the other solenoids. Also, I assume that there is a junction somewhere where they split to the three solenoids.
I can try to take pictures of where the wiring gets to the solenoids if you want.

Regarding your question; if the changeover switch was always on ‚left‘, you always need to return fuel to ‚left‘ and must live with half the fuel capacity as well as bad fuel or rust in the right tank. I wouldn’t advise the usual bodge because I‘m positive you‘ll fix it sooner than later. It isn’t all that complicated, always think: three valves, one switch, on or off, return flow to source tank always; and disregard the rest. For now! Jochen has the right drawings but somewhere the whole plumbing is shown.
Good luck.

The long wire, could that be it? Quite sure. The short one is the fuel sender. The long one routed along the tank seam at the bottom with small Steel clips. Check the valve with a battery before you put it all back together. The return flow has no pressure but vise grips (or a plug) are helpful when you remove it for testing so there is less spillage.

Oh, also: tank removal was a real pain and much use if nothing leaks. You should however drain and flush the water from the tanks - Drive tanks until empty and open the drain plugs. Be prepared for gas, rust and water; have a new seal ready. Of course you can do them separately.

'What seal are you talking about since I am thinking of dropping the

The rubber seal for the drain plug. You can find the pert number online. Why would you like to drop the tank?

Look at Jochen’s parts catalogue posts for some possible clarifications, Lee…

Part #8 shows the right hand return valve (?), with two wires, going through a cover, #7, to ‘somewhere’. Is this also the case for your installed ‘left’ valve - or are the layout different 'left and ‘right’? The point is if the set-up is ‘sided’ - different between LHD and RHD, however unlikely?

Has your(!) ‘right’ (and ‘left’) valve two wire connectors and a corresponding cover? If so; have you looked behind that ‘right’ cover…? The wires may be there, but not threaded through by a sloppy worker? :slight_smile:

The wiring diagrams shows a single wire going from the changeover switch, supposedly feeding both return valves and the changeover valve. However; the changeover valve also has two wires, one pos and the other a ground wire. - the same likely applies to the return valves? You say ‘one wire’ on the ‘left’ goes to the front - is there only one wire…?

In any case; a pos wire circuit going to each valve is implied, which are joined ‘somewhere’ - and a separate conjoined ground circuit, or valves are individually grounded…?

And to be sure; does the installed ‘left’ valve ‘click’ when power is applied…? Ie, is the valve actually closed with ‘right’ selected…?

All this does not offer an easy solution - but can you clarify my questions…?

xj6 85 Sov Europe (UK/NZ)

Of course it does! What you say is look behind the cover on the drawings I posted, else follow my instructions.
Short of taking apart the whole car over a wire, take power from one of the other two valves. I assume though that the four-wire connector can be accessed via the light assembly and the wiring runs down and forward. The grounding points are on the famous wiring guide (S-51?), but a new one should be easy to make as power, not ground is switched.


Okay as I suspected someone previous had removed the tank and did not replace it properly. The wiring harness was caught above the tank and was not visible and obviously not connected to the return valve etc. Dropped the tank and found the harness and will hook back up. Wondering however if there is any way to check out the return valve without removing it? The hoses are almost hard as a rock and if I remove I will perhaps have to change out all of the hoses which is no fun. I believe the fuel return is to the bottom of the tank not the top is that correct? Seems like there is no good way to check out the valve without removing it and I hate to do that if it is working. If I put the car in reverse and turn on the key the fuel pump will run I believe. Since the engine is not turning will the fuel then be completely returned to the tank? Would this be a good way to check it. If the valve does not open what will happen??


There is an excellent write-up by Doug Dwyer in the Jag-Lover Frequently Asked Questions (FAQ) page that should answer all of your questions.

Here’s the link: http://www.jag-lovers.org/xjlovers/xjfaq/index.html

Look under the “Fuel System”.

While you are there you should check out the wide range of helpful FAQs. Many of the common issues with these cars have nice write-ups that are as pertinent now as they were when they were written years ago. I use the FAQs and Jag-lovers archives regularly when researching solutions to my Jaguar mysteries.


Correct, there was a relative thread recently.

Yes, but only for a couple of seconds.
Either disconnect the fuel pump relay and short the fuel pump pins (30 and 87- the ones at the center of the plug), either power the pump directly from the battery /power supply.


If the valve does not open, and assuming that the other return valve is also closed, the pump might buid excessive pressure, not a good thing, but you will hear the pump forcing and slowing down…
You should immediately shut it off in case this happens. .

One way; select ‘left’, start the engine, then clamp the ‘left’ fuel hose between tank and changeover valve - the engine should die as fuel in the rails is depleted. Repeat for ‘right’ selection, clamping the ‘right’ fuel hose same result.

This positively confirms that fuel is passing the changeover valve correctly. If the engine runs on with hoses clamped as described; the valve is not closing properly - allowing feed from both tanks.

An alternative, instead of running the engine; remove air filter and prop open the AFM flap. The pump should now run with the ign ‘on’ - and the result of hose clamping, as described, can be observed by listening at the filler lid for fuel return. No fuel return, no fuel through the changeover valve.

This test requires that return valves function is first confirmed…

With reverse selected; the pump will run as long as the key is held to ‘crank’ - but this is impractical for testing fuel feed/return. Shorting fuel relay base white to white/green will indeed run the pump with ign ‘on’ as Aristides says…

xj6 85 Sov Europe (UK/NZ)

Thanks Frank. I am going to try your AFM flap idea. You can hear the fuel return even though the fuel return is at the bottom of the tank is that correct? Lee

Where or did I get the idea that the fuel return is at the tank neck ? And if so, visible with the cap open and the fuel pump in action.

And. or the fuel return is governed by the fuel pressure regulator. Up front in the engine bay. Start there to track the line back to a split and thence to the tanks.