Whilst in the process of removing the original tanks from my 1975 series 2 to replace with series 3 I noticed what looks like return lines below the filler necks. Down below next to the feeder to the external pump there are blank plugs. They can’t be vent pipes because they don’t vent anywhere.
Until I can get at least one of the tanks out to to blow some air through the line is anyone au fait with the internals of some carbed series 2 tanks that had blanked off returns fitted?
This would make things so much easier. I’ll just use my original tanks for the injection and flog off the series 3 tanks. I’ll just have to get bigger pipes to the pump.
It’s a bit complicated, Don; at some stage one would expect a ‘75’ tanks to have venting spigots only - no return spigots.
However, tanks would be prepared for both the US closed ventilation system - and the ‘European’ plain open air venting. In the former case; the vent spigot (tank ‘neck’) would be connected to the fuel separators in the C pillars - and from there to the charcoal canister. However, the fuel separators would then be connected to a ‘bottom’ of the tank spigot - to return liquid fuel back to the tank. For European markets, with open air ventilation, this return would be unnecessary - and may well be blanked off.
It is of course very important that tank venting is not blocked whatever the market. Whether the ‘75’ was prepared for future fuel injection returns is an open question. The Series 3 tanks certainly were - but when carbs were fitted the fuel return from EFI may or may not be blocked at the tanks in either tank version…
However, it is uncertain to what extent Jaguar went in in actually connecting, with hoses, the various tank spigots - and blocked use elsewhere…
With carbs; your main concern is that the tanks are vented - all other spigots or connections may be blocked. Just make sure you know which is which…
So the plot thickens. The only ‘venting’ that I can find is the little holes in the filler necks connected to hoses going off somewhere.
The blanked off spigot(s) next to the pump feeds have little threaded brass plugs. In the parts book with numbers C.36681 they are listed as ‘PLUG RETRNPP’. In my haste to avoid pulling the tanks I took this to mean they are blanking plugs for unused returns.
But does this mean they are returns for the separators and not for injection? But can I use them for EFI returns?
I am in Australia. My flag is for solidarity with Ukraine.
Exactly like all early non-US/ North American XJ6’s, that is just like mine, #2J50041DN.
The hoses from the fuel filler necks go down inside the rear wings to a connection with a hole in the rear wing and into the atmosphere.
The LH one was blocked by a metal object inside the tube when I bought the car in April 2007 which created vacuum engine n the tank, I had to drive with the lid open until I fixed it. It required opening both the boot (trunk) trim and the lower wing, reniving the rear bumper and exhaust muffler/damper etc.
This must mean in series 3 and other tanks there are two returns. One for injection and one for separators. So many variations . In a series 3 XJ12 tank I have there is just the pump feed at the bottom. The FI return appears to be at the top but in some diagrams this is labelled as ‘venting’.
Anyone know where to get 9/16x24 UNS male plug to plug the lower front return port in the series 3 tanks? I’m sort of in this same tank replacement mode as we speak.
Bill
Thanks for that, I did have a squiz but still I am not sure of which spigot to use for the fuel reg return to use. Apart from the fuel feed there is one bottom and one top spigot. Car has a previously carbied lump, now out after a rebuild and with injection.
On ROW S3 models without recovery the caps are vented, there’s a tiny hole in the filler neck and a hose goes into the C pillar. I believe they too have the loop in the C pillar to aid in recovering as much as possible.
On early SI the vent is in the cap itself and designed to open when a bit of pressure differential has developed. It’s easier for air to go in than out, so there is little smell.
Thanks for all the super helpful replies and advice.
I think I have read just about every topic relating to tanks and returns both here and on other forums and I am now back to square one.
The spigots on my series 2 are indeed for feed and returns but both are only 6mm so are not suitable for FI, only carbs.
I have a left hand series 3 XJ12 tank which I can use but the series 3 RH tank is different again. I might have to just bite the proverbial bullet and buy new tanks but at $1200 a pop I’m losing interest.
As I have already bought a 6 port Pollak valve it would be a waste to give up now.
Biggest problem atm is getting the mufflers off to get the tanks out
Don…
The only tanks that I remember seeing the two spigots side by side was on a 75 XJ12 that I had. It seems like the 75 XJ6 used a tank similar to the earlier carbed cars, but somewhere along that time the XJ6 also had another variation of tank that had internal pumps, with a large cutout inside the fender well to access the pump… Seems like that may have been 75-76 XJ6…
Jaguar did a lot of experimentation with fuel pump and fuel return placement during that time it seems…
For what it’s worth mentioning, the 75 XJ12 was fuel injected… So if your tanks did indeed come from an XJ12, chances are it was set up for the fuel returns on an injected set up…
Cheers,
David shop.EverydayXJ.com
Thanks David, the issue is the size of both the pump inlet and return lines in the original tanks, both being 6mm. I can’t imagine that size plumbing working well in a FI V12. For the Sniper EFI to work the ID must be 10mm and 8mm respectively. So Ive read anyway.
The XJ12 tank I have sitting on the bench has 8mm for both but would probably work but I only have one.
Admittedly I’m not familiar with the Sniper EFI… I assume you’re going with an “other than Jaguar” engine? If so, you might reach out to Andrew at Jaguar Specialties to see what he recommends…
There is also a forum here called Lumps, that may have some answers…
Cheers…
Yes thanks for the link I will have a look. Helpful as always.
I have posted about stuff in ‘Lumps’ before but in this case I was trying to keep it as simple and generically Jaguar as possible, eg the the functional aspect of Jag tanks and plumbing in both carb and injected cars.
Now I’ve learned both series 3 XJ12 and 4.2 tanks will work for me.
At this stage neither the Sniper nor I care about up front as long as it’s going to work at the back.
Bear in mind that actual petrol consumption is in the same ball park whether carbed or injected, Don…
However, carb bowls is sort of reservoir for sudden increase in petrol consumption - fuel is delivered into the air flow/manifold by atmospheric pressure. With EFI; fuel rail pressure must be kept constant, at some 36 psi. Fuel volume, reservoir, in the fuel rail is small - so with with restriction to the pump by a small hose; the rail pressure may drop and cause fuel starvation.
Hence EFIs, and certainly with the original set-up likely needs larger hoses to feed the fuel rails. I’m not familiar with your ‘Sniper’ set-up; it may work with the smaller hose, like with a single point injection - and 6 mm may be adequate. But I would not bet the farm on it…
As an aside; with EFI the fuel pump is always running at full capacity - the pump return is just the bleed-off to maintain constant rail pressure.
As for vent and return hoses; tank venting spigots must invariably be above full tank fuel levels - no ‘ifs’ or ‘buts’. Likewise; the fuel pump return must be high, above fuel level, otherwise the ‘back pressure’ on the fuel pressure regulator will incur variations in the fuel pressure depending on fuel level in the tanks…
The return from fuel separators, when used, is at the bottom of the tanks - pressure variations here are immaterial. And if the closed vent system is used, venting to open air, there is no need for fuel separator vent hoses…
I suspect that during transition periods the tanks were fitted with spigots to accommodate both carb and EFI - and for all markets. Unused spigots were just plugged - and one of the blocked spigots may be a larger pump feed…?
But two spigots above fuel level is required for EFI - tank venting and pump return…
Thanks Frank, the 6mm feed is from the tank to the pump, maybe 30cm then goes 10mm to the engine with 8mm return to 6mm inside the tank so as you say both likely to interfere with both fuel delivery, and I suspect the regulator.
It is indeed a throttle body injection but as you suggest I wont be betting the farm on those smaller hoses, regardless how short they are being adequate.
. In a series 3 XJ12 tank I have there is just the pump feed at the bottom. The FI return appears to be at the top but in some diagrams this is labelled as ‘venting’.
