I have a 1984 XJ6. The issue I am having is when I select the right fuel tank all the fuel from the left tank transfers to the right tank.

I did all the electrical checks to the three switching valves. The power was there and I did have sticking valves.

I replaced all the valves with new valves. Did all the electrical checks and they check out OK.
The left tank normally open valve closed and the right tank normally closed valve opened. In the trunk switching valved worked correctly. Normally open from left tank and normally closed to right tank.
I performed these test with the fuel lines disconnected and physically blew into the valves. Worked as they should.

I hook up the fuel lines and reassembled everything.
Left tank worked great switched to right tank and the problem still exists. Left tank fills up the right tank and pours out the right filler cap.
Went back to check voltage and everything worked as manual states.

I replaced the dash switch with a new switch even though all electrical systems were working right.
Installed new switch and problem still exists.

Went back into the trunk to the switching valve and removed the left fuel line isolated the left tank from the right and started the car problem still exists.
This told me that the switching valve was doing its job and not sucking fuel from the left tank when the right tank was chosen at the switching valve.

Then I went to the wheel house valves and checked for voltage and the left valve was electrically closed and the right was electrically open.

I then physically clamped off the left tank by means of pinching the rubber gas line between the valve and the tank and only then did my problem corrected itself.
I then un-did the clamp and problem came back.

I then pulled the electrical wire off the fuel pump without turning off the key so the power remained to the left valve.
I pulled off the rubber gas hose between the valve and the fuel tank to make sure the valve was closed and it was, like it should be.
Turned the pump back on and switched tanks from right to left and fuel came out left valve like it was returning to the left tank. Switched to right tank, fuel stopped at left valve, valved closed.
So now I know left valve was working.
I now put a rubber hose on the tank side of valve and put it into a gas can eliminating cars fuel tank. The fuel tanks were replaced 5 years ago with new ones.

Turn on pump and the right tank started to over flow. with fuel being drawn from the gas can.

I think this tells me that the ball check in the valve leaks fuel back past the left valve. Its a syphon effect caused from the fuel returning from the engine to the right tank.

I have physically blew with my mouth into this valve. One way toward the tank the valve is open and when electric is applied it closes.
The other direction from the tank back the ball valve will close. If I blow the ball open, I can blow softly and the ball will not close because it is not spring loaded.

I am at wits end and do not know where to look for a solution to this problem.

Do you have any suggestions? Is there something I should possibly change?

Thanks for your time

 

Is there any chance the fuel return lines have been accidentally swapped?
If not...maybe add a 92 liter center tank? ;-)

 

Fuel line are not swap. I have this car 25 years and did a complete restoration on her 20 years ago. Everything was working well. Both tanks would switch and drain with no issues.
When the right tank first over flowed I checked the return valves and the left was stuck open when it should have been closed. I replaced these valves 20 years ago and only put 16,000 mi in that time. Sitting does not agree with these cars so I decided to change the three valves with new. And the issue still remains. I just looked into the tank to see if the return line was off and everything looks like new. The tanks are only 5 years old. I would wonder if the tank return is high in the tank how can the fuel be sucked from tank. Even so the check valve in the return valve should hold back the fuel from going in the opposite direction also the valve is electrically shut. Thanks for your imput.

 

wow, I'm impressed at your troubleshooting skill but I have no clue what could be causing this.

mine is a 1984 too, but I've never replaced any of the three valves or had the issue, although I did replace the right / passenger side tank around 1995. I've owned the car since 1989, most reliable car I've ever owned.

my questions: did this start all of a sudden, or after you replaced the tanks? Are the tanks the aftermarket kind made in Canada?

I don't know why something rings a bell with the tank itself causing the problem.

 

This problem started all of a sudden. I had a injector like that started to leak so I changed that. Took her for a ride and came back noticing my paint by the right tank cap was yellowing. Pond further investing I popped the cap and the tank was full to top and fuel ran down top of car and also out overflow beneath car. This is a common issue when these valves go bad. Knowing this I check the valves and the left valve was stuck open. So I did not mess with them I replaced all three. And the issue stills exist.
I do not know were the tanks were manufacture I did purchased then off the internet from Jaguar. I know I paid more that the ones that are listed today.
I will search the internet for tank issues.
If there is a tank I do not understand why it tool this long to surface.
Thanks for a possible new lead.

 

oh, so you replaced BOTH tanks? what do you mean "purchased from Jaguar"?

could it possibly be a stuck Sender Float inside the tank in question?

 

If, as you say, the lines haven't been swapped by mistake, the quick and dirty fix would be to swap them now....

Also there has nothing been changed on the electrical side? Maybe some swapped leads to a relay?

 

I purchased these from the a internet site that strictly deal in Jaguar parts like Jagbits, Welsh, etc.
I would hope these dealers are only purchasing quality stuff. If they do have an issue, I would hope they would contact the purchaser of such items. It is good business practice.

Sender Floats would only read fuel level sending the information to the dash gage. In my case both sending are relatively new and are work as they should.

 

ok, then the obvious is that one of the valves is not closing when it should. What else can it be?

as you stated: "I then physically clamped off the left tank by means of pinching the rubber gas line between the valve and the tank and only then did my problem corrected itself. I then un-did the clamp and problem came back".

 

I do not see any way that the fuel lines could be swap. They are hard line to each valve changing to a rubber line on either side of valve.

The valve it self has two black leads and the car has one black and one white with black stripe. I did think the same so I reversed the wires and valve worked the same.

The valve themselves should not be swap. One is a normal open valve (left) and one is a normal closed valve (right). They correspond to the trunk switching valve. If they were switched I would have created the same issue I am having, only it would be happing to both tanks.

 

I know it does not make any sense, but The valve itself is closing electrically.
I proved this by putting a hose from the valve into a bucket, to physically see what happen. Left tank chosen fuel flowed, switched to right fuel stopped, valve functioning. Put hose into bucket of fuel and fuel was drawn back to valve and right tank overflowed. There is also a check ball in valve on tank side to (I assume) prevent this from happing. I think is a syphon of 38 psi of fuel returning to the right tank drawing the fuel backwards into the left valve. The ball valve in the valve itself is not spring loaded so it could very well leak. And the seat in the valve itself could be directional.

I did read on a forum a fellow had the same issue and he never got an answer.

I did order in-line check valves which I will get today and I am hopping they are spring loaded. I am thinking I will place them between the valve and the tank.

 

Yukscn,
This is THE most frustrating aspect of these cars! Far beyond lucas or motor issues. I have found that the return valves will leak when new, like you said the ball valve doesn't seem to have a preload spring.
The first thing that comes to my mind here... the valves can be put back in turned around backwards, I'm hoping that's your problem. I've done practically the same thing you've been through here, all NEW parts, running great for 2 years. I let the car sit for a few months for a starter problem, got her running again and guess what ...fuel all over the side of the car.

Do contact RogerMabry on the forum though, he's changed all the valves out for a multi valve used in diesel trucks with good results, I may end up doing the same. Another lister has simply T'd the tanks together with no valves, also seems to be working ok (don't park on the side of a hill for long periods though).

 

Also, I can't really see how the tank itself could cause this problem, and fuel additive def won't help the situation. Do check those pesky vapor lines at the top of the filler neck for cracking and the back glass area for perforation. Both lead to water in the tanks.

 

When I think about the tanks I think that the tank when full should have 90% of its volume is gas and the other 10% is air. The return fuel return line should be returning fuel into this 10% air area. As others state open fuel cap push down flap and you can see fuel being discharged into tank. And I do see this happing. So If this is how the tanks are supposed to work fuel should never be able to go bleed back though re-turn line! Unless the internal tank return tube has developed a small pin hole somewhere in the 90% fuel volunm area allowing this syphon effect i described to draw fuel out of the left tank. I pulled fuel tank sending unit and everything looks like new although a pin hole could have developed and even with a pin hole the return tube could act normal demonstrating what I see when I look into fuel cap.

I did look at vapor lines and they are a part of this 10% air volume of the tank.
I feel if these were or something was obstructed the system would draw a vacuum and start collapsing things or starve the engine of fuel. Usually if anything goes wrong in this area it causes fuel vapor smell inside of car.

 

The valves are not backwards. I did think the same so I went back and removed them retested to make sure the new ones worked (again). I doubled and tripled checked things. And I agree when these cars set who knows what to expect
next.
I will look to see if I can find the article you talk about. Any information is appreciated.
Jaguar should have taken a idea from the Sunbeam Tiger. It had two tanks one in each fender well with a 1-1/2" steel tube joining them in the trunk and one filler cap. One tank filled the other and only one fuel line to carb.

 

Up date:
I installed a John's Cars (www.johncars.com) Tank Tee Kit for $23.00. Problem solved. This kit joins both tanks and when the fuel gage reads empty both tanks are empty. At pump you fill both tanks as normal and fuel will seek its own level. The fuel tank switch on dash will read either tank and they should read the same.

I did the kit a bit different John's TEE went in place of the switching valve in trunk and I installed two Airtex CV8000 check valves under each fender. In the process I did discovered the harness plug on the dash switch may have been over heated at some point in time. I removed the harness plug cover and cleaned and squeezed the blade conectors fighting them up for a snugger fit. Could have this been my issue all a long! Don't know at this point in time. Even though my valves were working maybe they were not getting the voltage the needed and were fluttering. If you any type of issue with this circuit first check harness plug for a good connection.

 

Glad you got your problem resolved. I have taken out the Jaguar switching valves from two S1 over the years. I use a Pollak valve that comes in three port or six port variations depending on whether you need return lines or not.

It is easily installed and costs less than $100 USD.. replaces all the Jag tank stuff... it instantly switches from the stock the Jag dash switch.. I use pre tank filters and in my current V8 version with fuel injection I have a post valve filter of the proper type. The one shown is for a carb unit with no return line... I currently have Spectra tanks for a S3 with the S3 filler caps as I needed return lines for the FI upgrade.. will have to take upgraded photos someday.

It all fits in the spare tire well with lots of room to spare...I tried to include a wiring diagram but it will not accept .ppt files and their .pdf file showing how it all works is included..

Just a modern day upgrade to fix all the old Jaguar tank switching and over filling problems.

 

Can you elaborate a bit on this?

Cheers
DD

 

Airtex check valve

 

I had not heard of this mod by John's Cars, but then I thought he had stopped making mods for XJ-6.

Sounds interesting and will check it out.