OK, so I stripped down my SIII Lump to determine where the far side tank is leaking. I found two pinholes in the bottom which based on what I can see inside are surely caused by rust. The problem is that I have no bloody clue what kind of higgerypokery the original owner got up to when he linked the two tanks together. It's a ridiculous mess at this point. There is only one feed line left, that comes from the near side. The only return line goes to the far side. This would explain why the far side tank had 5 gallons in it when I've never filled it, but it doesn't explain the disaster of plumbing that is my boot/undercarriage.

Does anyone have photos of a stock fuel system (or can anyone provide them) with labels for what is what? The boot is my primary point of confusion. There are two nipples that enter the boot at the spare tyre well and in my case, both are connected to a tee which is connected to the fuel filter so I assume both are feed lines? I have no clue.
I'm going to bodge-patch the rust holes in the tank to get my kitty back on the road but I'd really like to sort the hackery of a fuel system out so I can just delete the far-side tank and not have to spend the money to replace it (the only feasible long-term solution I can figure). Any help is GREATLY appreciated!

 

With so much missing, I am not sure where to start. If you fix and replace the near tank
and use a T to connect it to the far side. The tanks will balance. The one return would suffice. The third leg of the T would thence go to the fuel pump and on to the fuel pressure regulator and thence to the injectors. No switchover gear involved. Actually one fuel level sensor would suffice as it should read both tanks via one sensor.

While it would probably work that has an inherent flaw. No side hill parking with full or near full tanks! The right side fuel would rush to the low side. if not enough room, it would overflow. Not good.

Were it my car, I would seek to get the valving to restore it to where it was when it left Browns lane!!

Carl

 

The stock photos are from a '84 S3 that I scrapped.

Six port valve is Pollak that I use - get rid of the old Jag junk....

 

I am assuming you are still running the XK engine with its original fuel injection system.

The feeds from each tank come out the inside face of the tank, pass across the bottom of the silencers, and into the spare wheel well. I think they secure to each tank with an olive screwed into the tank, but the other ends just use rubber-type petrol pipe. Feed pipes are of steel, about 1/2 across, and each pipe is then connected into a changeover valve that switches each tank to feed the fuel pump. My car had the fuel filter in the engine compartment, but later cars had it in the trunk near the pump. The return pipes don't enter the trunk, they come back along the underside of the car, into a T-piece, then there is a pipe to each tank with a valve to close or open the return feed. Each valve works the opposite to the other, so they are handed. One opens on voltage feed, the other closes. The changeover switch on the dash controls all three valves, and the feed from the fuel gauge transmitter in each tank.

Sounds simple, don't it (not !!)

Modern cars eliminate the fuel return with the pump controlled electronically to send the right volume of petrol depending on engine demand. In the 70s things were more simple !!

 

Thanks all! Roger, those photos help. Mine is indeed a hack-job, as I suspected. The two feeds are just teed. I still don't know what the whole loop-around-whooptie-doo is with the fuel filter. That little block that splits off into two spots out of the boot well?

Fraser, thanks for the tips. It all helps even though I'm not on the XK anymore. It's been lumped. Prior to my ownership, of course. The only thing that remains of the XK is a valve that was left in the jack bag covered in the kind of slag that can only indicate a very tragic end to the old XK mill.

For the time being, I went the cheap route and used steel epoxy to patch the two pinholes in the tank. No more dripping petrol and my car goes! The sill panel was just caked in petrol sodden road grit, so I suspect that's what caused the holes to begin with, the grit got wet and rusted it from the outside. The tank is quite solid except for those two little holes. I flushed it with copious amounts of sacrificial (stale) petrol and it all came through clean. As near as I can see, the tank itself is fairly clean inside as well. In any case, this should get me through until I can find a way to delete that tank or even go drastic and just put a fuel cell in the boot.

Still, if anyone has more detail on the plumbing in the boot, post filter, it would be very useful!

 

If the car no longer has the original XK engine with its L-Jetronic fuel injection system, then all bets are off. Is the 'lump' fuel injected, and how does that operate ? Carbed engines normally need low-pressure pumps, and there is no fuel return needed.

Whatever; you cannot really keep the original layout, apart from the two feeds to a changeover valve. From then on, it depends on what the fuel system is for the engine.

 

Yes!!

Carb'd engine takes you down one path and FI takes a different path. although some carb'd engines do utilize a return line.

My lump uses the Jaguar delivery line and return lines and vent lines as they were installed on Brownslane.

But, a cross over is needed in the engne bay as the LT1 fuel rail has intake and return on the driver side. LHD car. The LT! fuel rail has it's regulator right there as well on the rail.

So far so good. didn't need to reinvent the system.

Carl
.

 

Aye, I did leave that little detail off, didn't I?
Mine's a really fun one in that everything still runs the same. I have a throttle body injected engine (think a two bbl carb with the top lopped off and two injectors grafted in, if your not familiar). The feed is on the near, return on the far side just like stock, uses the same pump as the pressure reg is on the injection body itself... it's a dream as far as tracing back changes because not much needed to be changed. The problem is that I don't know what it should have been to begin with, so I've no metric to go from.
In any case, she is running good for the moment. No leaks from that tank and no petrol odor inside the cabin anymore (at least I finally know what was causing that).

 

Please note that I am describing something I worked on 25 years ago, so it may not all be right, but hopefully Doug Dwyer will correct it !

Based on what you say, I would return it to stock if possible, to maintain the fuel return lines you say are needed for the EFI on your "lump".

So if you haven't got it, you need: -

- Original fuel pipes and olives from tanks into the trunk.
- new (or used) electric changeover valve.
- new original (or recommended substitute) fuel pump
- pump pressure relief valve ( this is not the one in the engine compartment, but limits the pump pressure into the fuel line, by allowing blow-off back to the inlet side of the pump). The other one on the fuel rail maintains fuel pressure at absolute levels based on inlet manifold vacuum
- two fuel return valves (LH & RH, they are not the same, even if they look it !!)
- fuel line to fit as necessary.
- fuel line clamps

 

So here's a fun little bit of additional information. The car is leaking again. Same tank, new hole. The obvious permanent solution at this point is to replace the tank, which is my plan. However, here's the curious bit... both times that it's started leaking, it's done so the day after filling up with non-ethanol petrol. Does that make any sense to anyone?