Nov 1977 XJ6. Left hand fuel tank is cutting out when 3/4 full, whats needed to fix this?

 

What do you mean it's cutting out?
Fuel is no longer flowing from it?

 

Thanks jordanmc. Symptoms are, when running on the left side full tank, as the fuel gauge gets down to about 2/3 full, the engine appears to starve for fuel as though the tank is empty, and I switch to the right side tank.

 

That is strange. If it were me I would take the trunk apart so that you can see the pump and fuel switching valve (that's how my 79 is setup) I would clamp off the hoses from each tank that enter the "t" of the switch valve. Pull the fuel line from that tank and shove a smaller tube in it so you can lengthen the line and run it into a empty fuel container. loosen the clamp and see if the fuel flows out of the tank. Could be that the tank is rusted out and debris is clogging the lines.

 

The car was built in Nov 1977 and has "in tank" fuel pumps, accessed from the wheel arch, the senders are got at behind the rear light fittings but I have no idea where the switching valve is located. I wonder if the sender has gone belly up.

 

AHA, so a late S2 carby car,

I would do the same driving test with the tank filler flap released, just in case its a vacuaming of the tank issue, but I doubt it, but we have to start at the beginning.

The fact it appeasrs to get to a certain level before playing up, heads me firstly in that direction.

Then the fact you change tanks and all is OK, has me thinking the in tank pump is getting lazy, or maybe the sock intake filter is sooooo clogged its starving itself of fuel.

Everything else I can think of quickly would affect both pumps.

 

I wonder if the sender in the left tank could be faulty and thinks the tank is empty, where is the switching valve located, maybe it needs testing too.

 

+1 . . . AHA indeed . . . Gosh, he's good . . . Gandolf is a ***** compared to our Grant . . . The Wizard of Oz!!!

But where were you, mate, all of 35 years ago, when Chris and I nearly went beserk with just such an issue in the beautiful gold Daimler VanDen Plas. Yes, it was a SeriesII also, but EFI V12 . . . went into "fuel starvation" mode just as our OP [GeoffBrown] describes, but would always come good within minutes of resulting roadside sit or tank changeover. More prone during night-time 1000Km run back to grandparents for Christmas, with boot crammed and kids sleepy. Checked fuel delivery time and time again . . . opted to put up with cough, splutter, change tank, all throughout the night . . . but Santa was not amused!

Found culprit just as described. Popped the fuel tank cap to a mighty inrush of air . . . blimey, it nearly pulled me, Donner & Blitzen all into the tank too. Problem resolved at Grandma's . . . not the fuel delivery side at all, but the return or venting side. Now I know there will be critical differences on a carby car, Six vs Double Six etc, but these venting problems and resulting vacuuming on the late SeriesII should not be under-estimated. I believe that Jaguar introduced a change for NA that left the modified fuel cap sitting proud of the surrounding bodywork . . . perhaps Grant can tell us if this was related . . . alas, I have no idea.

Best wishes Geoff . . . coaxing the Mighty Wizard from his lair may have just pointed you to far less pain that we endured until correctly finding our fix.

Cheers,

Ken

 

OK. got the dreaded lurgies, and feel worse than last weeks leftovers, so if the following makes no senes, just wait till it passes and I can think straight.

Ken is on the track, but waaaaay toooo many cylinders, and the system he had issues with, is fixed by drilling a 1/64" inch hole.

The S2 6cyl Carby cars did not have a fuel return system, that was left to the utter confusion of the V12 cars.

The later cars, yours, has in tank pumps, and the switch on the dash simply changes supply to the selected tank, which fires up the pump AND the sender unit. Simple.

Venting on the intank pump tanks is NOT as critical as the external pump systems, but as the fuel leaves the tank, air must still enter to prevent a vacuam.

BUT, since the pump is imersed in fuel, ya still got more than 1/2 tank apparently??, the thing will keep pumping, it is that clever.

You switch tanks and the beast is alive, but what happens when you switch back, in say, 10 minutes??

My thoughts are the pump is simply tired, as said before.

If the tank unit dies, the gauge dies, thats all.

One thing to "look at", is the one way valve in EACH hose where it exits the tank. This is to prevent the fuel from the one tank simply filling the other tank, instead of the carbies. This situation you have is NOT normally one of their tricks, but still worth a look.

 

To Grant And Ken, Many thanks to you both, I will be out checking your vacuum theory and if needed other suspected possibilities as necessary. Cheers Geoff Brown.(the Gong)

 

Hey Geoff . . . Grant is the Wizard . . . and take heed of his set out of the V12 issues as not applicable to yours. Another of my senior moments that have my kids rolling their eyes! However, after following his advice to check your pumps for "tiredness" . . . could you nip over to Adelaide and check Grant out also.

He sounds terrible with that lurgy . . . so we wish him a speedy recovery. GET WELL, MATE!


Ken

 

Or:


The guage lies. The tank is empty!


Carl