Car: 1986 XJ6 Series III. 130,000 miles.
Present problem1: The dual fuel tank system switch has ceased to click between the two. Seems jammed. Have been advised this is a major repair problem and that it is mechanical, not electrical.
Question: could this simply be a faulty electrical switch on the dash? If so, how do I test for which problem it may be? If I am misunderstanding the system, please explain. Any fix suggestions are welcome.

 

The changeover system can be a little frustrating but in THIS case, where the switch simply doesn't seem to be clicking, I'd just replce the switch and see what happens. You can dig deeper if needed but any tests depend on having a working switch, so....

Cheers
DD

 

You can also just go into the boot, where the changeover switch is, and test with a test light or voltage meter at the switch...
When left is selected, there should be no voltage at the changeover switch...
When right is selected, there should be voltage at the changeover switch....

This applies to the changeover switches in the wheel wells also..

So if you hit the dash switch, and either of the issues above doesn't happen, I'd swap out the switch....

Of course I have a couple of used ones, and I think a new one or two in the shop...So if it turns out to be the switch, I'll be glad to get one to you...

Cheers!
David Boger
Everyday XJ

 

I have the same issue, I have bought a new fuel switch but getting in to the dash to replace it is puzzling me, does anyone know the best way to get in to replace the switch? Any help would be great I am a new user and new to jaguars

Thanks

Mike

 

First, pull of the A/C control knobs. Behind them, you'll find some nuts that have slots in them.. They need to be removed. You can usually do that with a screwdriver pushing in the slots counter clockwise... Some folks have went as far as taking a socket and grinding the edges until only some small knobs are left that fit the slots.. I have a tool made by Mac that does the job nicely...
Next pull the radio surround faceplate out slightly...
Behind the radio surround faceplate there are two screws that hold the trip computer surround in place.. Take those out, and the entire surround will slide forward.
That allows access to all of the switches, and the trip computer...

One thing to note, when you are pushing the switch through the front of the surround, it's easy to get the veneer caught on the switch, messing up the faceplate... So take that part kind of easy...

David
EverydayXJ.com

 

Can somebody explain to me how this system is supposed to work? I just got an '82 XJ6 and I don't really understand it. Can you run out of gas from the one tank if you forgot to switch over? Are these switch over valves and switches prone to failure?

 

There is a changover valve (in the trunk) and two return valves (one in each rear wheel well).

The changeover valve dictates which tank fuel is drawn from. The return valves ensure that any unused fuel is returned to the same tank it was drawn from.

Operating the switch applies (or removes) voltage from all 3 valves simultaneously. The return vales oriented opposite of each other. Application of voltage closes one and opens the other. Removing voltages does just the opposite.

As I recall selecting the left tank = "no voltage" (the valves "at rest", so to speak). Selecting the right tank applies voltage and activates the 3 valves.

Yes you can run one tank totally dry. I wouldn't recommend it :-)

The system is fairly reliable but with age and mileage issues do crop up. Long periods of non-use often creates more problems than frequent use.

Cheers
DD

 

Thanks for the info!

So suppose I don't want to mess with a second fuel tank, and from now on I just want to use one tank. How do I know which one is being used right now? Any way to test or know?

The buyer I bought it from used it frequently but did not seem knowledgeable, so I'm guessing the other tank (the one that's not selected now) has not been used in 10+ years (before she got it) and for now, I'd rather not use it.

 

How do I remove the fuel tanks from my XJ6L? There appears to be fuel seeping out the left tail light. Any help would be appreciated.

J Walls

 

I'll try to answer a few of the questions posted above...

First, to replace the switch, here is a detailed article explaining how to do it:
Fuel Switch Replacement

A brief explanation of how the system works..

When the switch is pressed in, to select the left tank..
No voltage is applied to any of the switches.
The changeover on the left side is open, the changeover on the right is closed, and the changeover in the boot is open to the left.

With the switch out, the right side is selected...
Voltage is applied to all of the switches.
The changeover on the left closes, the changeover on the right opens, and the changeover in the boot opens to the right.

If the tank appears to be leaking as high as the taillight, there is a seal behind the taillight, that seals the sending unit inside the tank. There is a chance the problem is with that gasket, or the retaining ring.
The easiest thing to do at that point is to remove the taillight, and see if it looks like fuel is leaking from that gasket...

Cheers
David
Everyday XJ

 

Thank you David. My xj is new to me, however I have had Jag's a number of years back 120, 140's. Loved them. This is a little different. It has a 300 hp chev 350 with th350 trans. Nice conversion. I love it. Very smooth and with the original exhaust very quiet. Cannot tell the difference in noise anyway. I too am having trouble with the fuel switch. I went to the boot and found that it had been modified as well. No solenoid's just 2 fuel pumps, albeit, they are new. I have a switch on order. Will let you know how it work's out. FYI I also have a Jeep Grand Wagoner with Benze 4.7 L roller rockers overhead cam's etc. Nice smooth also a great ride. I am retired and spend most of my time restoring older cars. Sorry about being wordy. It is nice to talk to people with the same interest's

Thank's again.
Jack

 

If not molested

Fuel switch out (white band visible around body of switch) = right tank
Fuel switch in (no white band visible) = left tank.

Re confirming which tank is being used. e.g. With fuel switch in/depressed it should be the left tank. You can confirm by looking under the flap in the filler neck with the car running, you should see return fuel (assuming the car is FI). Make sure you touch the car before you open the fuel flap just to be sure no static. Left tank is probably the one to use on a working system if you elect to only use one as that works with no voltages applied. Sounds like you dont have that choice atm due to previous owners habits.

Can also just confirm simply by topping one tank only up (the one you appear to have selected given the above) to confirm via the gauge if working.

 

I add the following:


1. Yes, if the selected tank goes dry, the engine will quit!! learned that in the middle of a busy intersection on the way to church one morning. A quick analysis and a punch the switch and the engine ran and all was well. A surprise, as my 85 Ford F150 4x4 had two tanks and a selector. But, if one went dry, it just continued to run on the other with no human intervention!!!


2. Memory work. Right in, left out is the tank switch function. There is a little white line, barely visible on the side of the switch to indicate in/out???


Why, the switch isn't a left right orientated rocker escapes me?


Carl

 

Jack...

Does your 350 conversion have a carb or is it fuel injected?
If it's a carb, is there a chance the fuel return lines have been eliminated?

In that case, the switch would only change power to the selected fuel pump (?)...

There was a similar two pump setup in some of the early Series 2 XJ6s for a brief period..

Cheers
David

 

This topic would have to be a candidate for the "How to" sticky surely. This thread is an indication that its a general recurring issue and an area thats easy to get confused in at first (1700 views already)

Just for info, here are some links I found useful:

Fuel Tank Switchover Checklist, Series III XJ6

Fuel Switch Replacement

XJS and XJ6 Fuel Tanks

 

David,
The chevy 350 has a quadrajet 4 barrel. I suspect the fuel return lines are no longer there. I am still figuring out the bit's and pieces so to speak. Am in the middle of restoring a 1969 chevy camaro. Installing a new 350 with turbo 400. In the middle of the process I am working on the jag. Hav a new fuel switch on order as well as a brake lite switch. I have noticed the wiring is somewhat under gauge. Hence it tends to break.

You have been a big help and have save me a lot of time and research. My next project will be the removal of the tail light. I will keep you up to date.

Thank you again.

jack

 

No worries Jack, Glad we all can help..

So with the carb, the return fuel lines won't be used... So you can ignore the comments about looking for return fuel to determine which tank is being used. All of the solenoids should have been eliminated too, though they may still be in place.
Sounds like the PO used the switch to activate the fuel pumps... However it's odd because generally the switch doesn't throw any power when the left tank is selected.
What I'd do is just use a test light to see exactly what has power -where, when you get the switch installed...
An odd duck for sure, and a PO modification for sure that you'll just have to sort your way through...

Cheers
David

 

Many thanks for the advice. I purchased a fuel tank switch and got very good detailed instructions for installation in the dash from David Boger at EverydayXJ. He is exceptionally helpful.



Also, many thanks for this Forum and the help in keeping these old beauties on the road.


Bob Morris

 

I see people talking about switch position for a specific side, mine cannot be the only one with a letter R visible when switch is out??? The arrows arent so visible though!

 

Pic didnt attach first on previous post for some reason..