My 1990 XJ12 is giving me grief because the switchover does not work correctly. It seems to either not switch or partially switch over the return. Furthemore, the fuel gauge is now always reading full so I never know when I'm going to run out of gas. It could be 120 miles, or it could be 20 miles. Now I'm thinking that I should T the hoses together and just be done with it. Anyone done this before? Is there a guide?

Thanks

 

Its been done. I've seen it described with pics in at least one thread. Not aware of a specific guide. Usual concern is siphoning between tanks if parking on an incline so one side of the car is higher than the other, which may cause an overflow. Backflow valves can prevent this, however (if am doing the mental gymnastics right) unless you fix the basic return issue you would still have a problem as the tanks would not self level.

My recollection from long ago is that hills aren't a big issue in Dallas and environs so you may get away with a simple T , if you dont feel like working on the problem.

 

Thanks, a T is the way I was thinking. I will do some testing first to see if I can fix it before I decide to rip it all out

 

Yes, I'm the one that provided the write-up. As long as one return line is working it will even out no problem. Never had a "hill overflow problem." Just dont park on a steep hill with the car tilted left to right (front to back is fine). The most important part of the install is to remove the spare tire, have the car outside on concrete facing uphill because you will spill some gasoline so you want it to have a safe path to flow down.
Jeff

 

Jeff, do you have a link to the writeup? Thanks

 

Before you do anything else you should verify that the change solenoid in the trunk is functioning properly, as well as the return solenoids in the outer rear wheel weeks (to the rear of the car behind a circular metal panel). Given the symptoms I would run a bottle of Techron (or two!) through the fuel system. While the dash switch may indeed be faulty, sticking solenoids are far more common.
The problem you describe is common to cars not used frequently. These cars suffer significantly from lack of use.

 

Looking for links. Here is an article by Doug Dwyer:
https://www.jag-lovers.org/xjlovers/...changeover.htm

 

Here is what I wrote in Sept 2020:
Replace the changeover valve in the boot with a 1/2" brass barb Tee. It looks like a capital T with push on barbs on all three sides. Then replace the return valves in the rear wheelwells with 3/8" barb connectors which are just a straight pipe with barbed fittings on both ends. In each case carefully tape off the electrical connections for the valves and just leave them there. Technically you only need to do one of the return valves but I did both. That is the short answer.

In reality it’s a bit more complicated because gas will go all over in the boot unless you drain the tanks first. Lots of posts here on the forum about replacing the boot fuel lines. Since you are going to be doing the messy part this is an ideal time to replace all the rubber fuel lines in the boot. I did not drain the tanks. Following advice on the forum I made a bunch of wooden 1/2" pointed dowels to use as plugs and I parked heading uphill and put big pans under the boot vents so any gas that spilled went out the vents and into the pans. With planning ahead I spilled very little gas. Be sure to do it outside (to reduce fire hazard) and not around grass (gasoline will kill your lawn).

When you are done fill up with gas and try the switchover dash switch and you can choose whichever gas gauge is the most accurate.

Jeff

 

Jeff,

Thanks, I plan on testing it once we get through this unusual Texas weather. If I can fix it, i'd rather have it functioning as designed

 

Re-engineering the fuel tank system instead of attempting (much more easily done) to clear the solenoids from sticking makes no sense at all. Just a suggestion from one who has owned more than 20 of these cars….

 

Understandable. And it isn't all that hard to do.

Bypassing the system in an option. I bypassed my changeover system once and, in fairness, had no issues. A short time later I was able to easily repair the fault by replacing one of the return valves.

The system is just one switch, a changeover valve, and two return valves. Not that complicated.

Cheers
DD

 

Fill up FAST. (greta gets angry)

 

I'm not going to comment on Greta but I sure like the twin fill-up method.

 

Minimizes the risk of the drooping hose marring your trunk paintwork when reaching across!

 

So I pulled the car around the back and inspected the gas tank lids to see if I could see fuel returning. My observation:

I shone a light into both tanks and could not see either returning fuel down the filler neck. What am I mission?
The drivers side tank gave a giant sucking sound when i opened the cap

What am I missing when I look down the throat of the filler?

 

There is a little metal flap at the top of the fuel filler neck. You need to push that out of the way with a pencil when you look down in there. When you are looking down in the fuel filler neck of the side that is getting the return (with the engine running) you will see a flow of fuel that looks like a weak drinking fountain.

The "woosh" when you open the cap is caused by a malfunctioning valve located under the right front fender. It is plastic with a rubber line on both ends.

 

Yep. I had a long screwdriver opening the flap and shoved my zippo (joke) as far down to look inside. I couldn't see a thing. I'll take another look tomorrow.