I've been working to get my 1980 XJ6 4.2 running more the 21 seconds after a long sit.
You all have helped a lot with my injector problems and the problem has worked its way to the tanks/switch/pump area.
https://www.jaguarforums.com/forum/x...oltage-224648/

I had been trying to clean both tanks but decided to focus on the right tank and leave the left empty till I got her running.

There was a small leak in the right side drain plug and by the time I got around to removing it (3 months) there was 1/2 gallon left where there was the better part of 5 gallons to start with.
Fixed the leak and added more gas. but she still only runs about 21 seconds. After it dies, there is no fuel on the outlet side of the pump. so my problem is in the fuel supply suction side.
I pulled the supply hose from the tank select switch and blew air into the tank.
Odd there was bubbling coming from the left tank that was empty!
So I pulled the left tank drain plug and my 2.5 gallon can was full and more still in the tank.
My question is ... Is this tank switching valve suppose to close completely? Can I clean it, or is it better to get a new one?
Thanks
Bobmo

 

The switch over and return valves are a constant problem. Start by cleaning the electrical connections to the three valves; that is the quickest and easiest fix. If it is still not working correctly you might consider plumbing the two tanks together with a 1/2" brass barbed tee fitting available at the hardware store. This will immediately eliminate all the switches and valves. Then after you get the car running well you can go back and work on the valve issues.

I spent a ton of time this summer trying to get my valves working properly. Took each of them out and checked them three times. Everything worked as it is supposed to but I was still getting gas moving from one tank to the other. So, yes, I think that some changeover valves leak when they are supposed to be closing off one side. I finnaly got it to work correctly by replacing parts until it worked right but boy was it frustrating and time consuming. BTW, plumbing the two tanks together lets you fill from either side but with a 1/2" fitting the fuel level takes about 5 minutes to equalize.

Jeff

 

Thanks Jeff.
But.. I drained the tanks, and connected the right tank to the pump with 2 prefilters in line.
Then I decided to see what was happening to the pump as I started it and ran.
There is 12V at the pump when I hold the key in the start position. as soon as I let go of the key the voltage drops to zero, and the engine runs until there is not enough pressure to open the injectors.

So anybody out there an electrical whiz??
I have checked the start and pump relays and diode pack so I'm thinking its somewhere in one of the other side relays or sensor thats turning off pump voltage when I release the key?

Bobmo

 

I am sure the wiring diagrams show all the components that need checked. If it was me I'd supply a known reliable 12v to the pump and see if that fixes it. Be vigilant to disconnect it when you are sure the problem is fixed. The worst problems are the ones that have two or three things wrong at the same time. I always try to jury-rig things to get it running then go back through hooking things up correctly until I get it all back together and running correctly.

Jeff

 

Take a look here. There are awesome step by step debug guides for fuel, both the plumbing and electrics

XJ FAQ

It walks you through how to determine why thinks ain’t right

Randy

 

Take a look at this trouble-shooting procedure.
Dave
https://www.jagexp.com/article/xj6-s...eshooting.html

 

No sensor involved

Offhand it sounds as though the pump circuit is not getting voltage from the Air Flow Meter

The pump circuit has two branches: starting and running

For starting the pumps gets voltage (via diode pack and pump relay) from the starter relay

For running the circuit gets voltage (via diode pack and pump relay) from the Air Flow Meter

Remove the ducting from the front of the Air Flow Meter. Reach inside the AFM and you'll feel a spring loaded flap. Turn the key 'on' and push the flap. The pump should run.

Post back if it doesn't

Cheers
DD

 

FYI, a lot of the guides on the Jag Experience site are the same as those found of the Jag-lover FAQ page mentioned a couple postings back. I wrote a lot of those 18-20 years ago

Cheers
DD

 

Thanks all!
Great resources that I will book mark!
Doug Your the MAN. Thanks for documenting all your work!
I'll let you know what happens later
Bobmo

 

I have a couple questions about linking the tanks--

To link the two tanks does the brass barbed T fitting just replace the fuel changeover valve in the trunk? Can you leave the two return valves in place or do they also need to be bypassed? If you don't bypass the return valves, will it still work if the return valves aren't working properly? (I believe mine are, but just curious) Are there any disadvantages to having the two tanks permanently linked?

I assume with them linked, after the two tanks equalize, if you push the switch that would normally change tanks, it would just change which fuel sending unit the gauge will be reading and that they should both read about the same.

 

Regarding the guage, yes all the switch does is select which tank it's reading from. Pick the one that is most accurate. As long as one fuel return valve is open it will work fine. One of the fuel return valves is normally open and the other is normally closed. You can see if they are working by opening the fuel filler cap, using a pencil to hold open the flap and then use a pencil flashlight to look down in there. With the engine running it will look like a drinking fountain stream if fuel is returning.

One of my SIII's has a perfectly functioning stock system and the other one has the tanks plumbed together. Plusses and minuses for each. If plumbed together dont park on a left to right hill with a full tank. But how often does that situation come up?

Yes, just replace the changeover valve in the boot with the tee fitting. I replaced my fuel hoses at the same time. The whole deal cost maybe $10.

Jeff

 

Thanks, Jeff! I just replaced the fuel lines last month so now that I know that disturbing old hoses won't cause a problem I'll go pick up a T fitting and see how it works.

 

Doug,
I had a small chance to trouble shoot some of the Jags Fuel ills.
The AFM flap doesnt make anything happen.
I pulled the connector and with the Key on
I got battery voltage +/- 11.2vdc, on the first and last pins and on the center pin ( 4th from either end) all other were 0 VDC.
I checked the end connections on the AFM with an Ohm meter, thinking that if the switch was working I should have continuity when I work the flap.
I got nuttin. which by most account would indicate a new AFM is needed.
Can I pry the cover off and dig around or is it permanently glued in position.?
Thanks
Bobmo

 

I'm not sure of the pin locations but the wires involved are brown/slate and pink/blue

With the key 'on' you should have 12v at the brown/slate wire. With the flap activated, you should also have 12v at the pink/blue, indicating the internal switch has closed.

Yes, the plastic cover can be carefully cut off and then re-glued into place. I can't remember whit the internal switch looks like but it should be obvious on sight. It might be repairable. Some guys just modify the switch so it is permanently closed. This works, but there's a safety concern in that the pump will operate whenever the key is 'on'

Cheers
DD