[xj] Fuel Tank Switching Problems

I have a 82 XJ6 and recently noticed that when I switch over to the left
tank it decides to dump all the fuel to the right tank. Is this a
problem with the fuel return valves and if so, which one.

Thanks,
Kirk Babcock
Oklahoma City, OK.

OK, Three valves.

  1. Changeover valve in boot. Tank selected with no voltage, lh.
  2. LH return valve in lh wheelarch. Normally open with no voltage to
    return fuel to lh tank
  3. RH return valve in rh wheelarch. Normally closed with no voltage.
    When rh tank is selected, this opens (and the lh one closes).

So if, when you select lh, and it pumps to the rh, the rh return valve
is stuck open. Check by running the engine, opening the tank caps,
pushing the flap open with a screwdriver and looking in. You can see
the return flow just below the flap.

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

From: owner-xj@jag-lovers.org
[mailto:owner-xj@jag-lovers.org]On Behalf
Of Babcock, Kirk
Sent: 28 June 1999 14:22
To: Jaguar Lovers XJ list
Subject: [xj] Fuel Tank Switching Problems

I have a 82 XJ6 and recently noticed that when I switch over
to the left
tank it decides to dump all the fuel to the right tank. Is this a
problem with the fuel return valves and if so, which one.

Thanks,
Kirk Babcock
Oklahoma City, OK.

Hi Kirk,

I have the same problem and have never tried to fix it. I found that if I
didn’t mess with the switch , the fuel would pull from both tanks at the
same time…but if I push a tank switch it messes it all up and does the
same thing. I’ll be interested to find out what causes this also. Thanks

Tom Drakos

“Babcock, Kirk” wrote:> I have a 82 XJ6 and recently noticed that when I switch over to the left

tank it decides to dump all the fuel to the right tank. Is this a
problem with the fuel return valves and if so, which one.

Thanks,
Kirk Babcock
Oklahoma City, OK.

I have a 1985 xj6 I started the car fuel began pouring pumping out what seems to be a overflow on the right tank so apparently a valve pumped all the fuel to the right tank and tank left tank ran dry the car quit running and motor does not turn over do you know how to fix this?

Yes. Fuel should come from and return to the selected tank.
Let somebody crank the car in ‚d‘ so the pump runs but not the starter.
Select the left tank. Button depressed. What do you see?
Return to right only: the switch has failed.
Return to both: the RH return is stuck open
Select the right tank. Report what happens. Is the right tank overflowing already?

**
Two different issues, Quin; engine not turning over is unrelated to fuel overflow - and vice versa.

Initial step; note changeover switch position that causes overflow - then select the other position. You can then usually run the car without overflow while investigating the problem at some leisure…

And/or address the non-cranking - which may be a discharge battery…

David covered the fuel overflow, but to test fuel issues at leisure; remove air filter and prop the AFM flap open. The pump should now run whenever the ignition is turned ‘on’…

It’s very important to listen at the tanks with the filler lids open - you should hear fuel returning as David specifies. However; if a tank is empty; pump will not deliver fuel from that tank - which will confuse the issue…

Be aware that fuel delivery; tank/pump/fuel rail, and fuel return; fuel rail/return valve/ tank are two separate circuits. The first is controlled by the changeover valve (‘from’ which tank -the latter by the two return valves (‘to’ which tank)…

The overflow is usually caused by fuel being taken from one tank, but returned to both (failed return valve) - gradually transferring fuel from one tank to the other. However, the ‘delivery’ may fail; fuel taken from the non-selected tank (changeover valve problem), but returned to the selected tank.

And fault combinations, though seldom encountered, can be utterly bewildering. As return is either ‘correct’ or ‘incorrect’ you must check that first, and rectify as required before proceeding - to avoid utter confusion…

As David says; check and report back…

Frank
xj6 85 Sov Europe (UK/NZ)
**

It was degrees today so I did not do much today but the car turned over fine today the right tank is completely overflowing all the way out the cap the left tank is empty now I will add fuel to the left tank tomorrow and switch to that tank and see if it will run

Is this the faulty part?

There’s three valves, this is one.
Check and report back. A gallon should be enough, you could siphon it from the overflowing tank.
How the engine turns over doesn’t matter. You don’t need that; fix the tanks first (not too hard).
Nice, clean boot area!

Quin,
That is the fuel changeover valve. When you select the left or right tank that valve is supposed to draw fuel from only the tank selected. Sometimes due to age, fuel tank debris, or lack of use the solenoid valve won’t work properly and fuel is drawn from both tanks, or the wrong tank.

Attached is a picture of the left fuel return valve circled in red. It is located at the rear of the left rear wheel well. There is another one located in the same location at the rear of the right rear wheel well. The way the fuel system is supposed to work is you select the left or right fuel tank using the fuel selector switch on the dash. When the left tank is selected fuel should only be drawn from the left tank and excess fuel not needed by the engine is returned only to the left tank. When the right tank is selected fuel should only be drawn from the right tank and only returned to the right fuel tank.
These two way solenoid valves can fail and get stuck in one position, the other position, or somewhere is between. This can make trouble shooting a bit of a challenge, but not impossible.
Follow the steps already suggested to see if fuel is being properly returned to the tank selected and only the tank selected. You can see this by looking in the fuel tank cap opening with a flash light and observing the fuel returning. If the two return valves work properly then your problem is probably the changeover valve in your picture.
I have experienced a few fuel transfer issues in my Series III XJ12 and two XJ6s over the past 19 years but knowing how the system is supposed to work properly has helped me troubleshoot quickly, purchase the correct replacement part, and get it working properly again.
BTW, I am a strong believer in installing aftermarket fuel filters (circled in red in the attached picture) between the fuel tanks and the changeover valve (circled in yellow in the second attached picture) to protect it from debris that accumulates at the bottom of the fuel tanks.


Paul

Paul…EXCELLENT explanation on how the tanks should work! A+!

Richard

Can I omit all these valves and still draw and return fuel to both tanks ?

No. What I had done after the changeover valve failed was that I substituted it with a ‚T‘. But it’s easier and better to just fix it, believe me. And I‘m cheap. :slightly_smiling_face:
Did you do the testing?

Quin,
I agree with David. You can not simply remove these valves and return fuel properly to the selected tanks. There will.always be problems.

Over the past 19 years I have watched as people posted about fuel tank switching problems and the many things that they tried to jury rig modifications that never worked properly. You will find these posts in the archives.

I think that if you spend the time sorting out what is wrong with your car (we can help with that) and fixing it properly you will be better off in the long run.

Paul

Subbing in a “T” fitting for the changeover valve will work, to a point. I have such a “fitting”. Knock on wood, unused, not needed, my car’s valving works as intended…

If one has a tot of fuel aboard and parks side hill on a steep slope, the “high” tank’s fuel will flow to the low tank. If there is no room there, it will overflow. On to the street., High hazard… Just a spark and…

Fixable, aye.

!. Avoid that park situation.

  1. Add “one way” valves, one for each tank.

Two means more work in addition tot he “T” plumb. So, why not fix or replace the bad valve???
The easy way r the hard way…

Carl

**
Yes, Quin - but as others have pointed out it is not really a good move…

With the ‘T’ replacing the changeover valve; fuel is drawn from both tanks. Fuel, returned correctly by properly working return valves - will migrate freely between the tanks. And tank levels will sort of equalise on flat ground…

With ‘T’ installed; omitting the return valves will return fuel to both tanks - again equalising, if required, via the ‘T’…

You can not(!) keep the changeover valve and omit the return valves - it will cause fuel ‘transfer’ between tanks. And eventual overflow will ensue - unless you pay attention and switch tanks as one fills up…

Changing a faulty return valve is easy. Just remember that the return valves are ‘sided’ - so make sure you get the correct one…:slight_smile:

As an aside; changing the changeover valve is also straight forward, but require clamping the fuel hoses before disconnecting - or you’ll have flood of petrol…

Frank
xj6 85 Sov Europe (UK/NZ)
**

The system operates as follows: there is just one circuit. With the right tank selected all valves have power. With the left tank selected the right hand valve is nc, the left hand no, and the changeover valve draws from the left tank to the pump.
For emergency fixes you can use the T instead of the changeover valve and it will be fine. But ever since I had done that I wanted the system to work as intended again. The coolness factor of the switch, parking at an angle, the ability to have some reserve, etc.

Ok so it was warmer outside today I was able to test the fuel tanks when the left tank button is depressed I see nothing and the car runs fine when the right tank is selected fuel begins overflowing out of the right tank until the left tank is empty and then the car runs out of gas in the left tank and the car stopped running

If it is a return valve where is it

It is the changeover valve you pictured earlier. First use a test light and see if it has power. If yes (with right selected, ignition on) it should be ~$80.

Good luck
David

Quin,
Your car should not draw fuel from the left tank when the right tank is selected. So it sounds like you have a failed changeover valve. This is the valve in the spare tire area that you sent us a picture of. The Jaguar part number for that valve is CBC4269 and they are available on eBay and through most Jaguar parts suppliers in the USA. I have no idea where in the world you live. If you need help finding this part just reply letting us know what country you live in.

What is the history of this car? Have you owned it a long time and this problem just showed up? Or did you just buy this car and you are trying to get it running? Fuel delivery problems seem to happen in cars that have sat undriven for a while. The valves do better when they are used regularly.

It is difficult to see the fuel returning into the tanks, but since you did not see fuel returning to the left tank when that tank was selected, it is likely that you may need to remove and replace the left fuel return valve as well.

When you change fuel tanks by using the fuel selector switch on the dash do you clearly see the needle moving to show the approximate amount of fuel in each tank?

Paul