Lee,
This was covered in another very recent fuel tank thread. The fuel return pipe enters the tank at the lower forward corner and inside the tank is a pipe that channels the fuel to the filler neck area. You can watch the fuel return to the selected tank with the fuel pump running if you open the fuel filler cap, push open the flap and look inside with a flashlight. Fuel should only return to the selected tank. This is one of the first steps of evaluating fuel tank changeover issues and is discussed regularly on this list
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Paul’s posts explain the lot, Lee - the ‘riser’ pipe within the tank exits at the filler neck area above petrol level of a full tank.
The reason for this arrangement is to avoid back pressure on the pressure regulator relating to tank fuel level - which would vary fuel rail pressure. Return could indeed have been at the filler neck, with the same result - but the way chosen was to simplify the external plumbing…?
There are various ways of running the fuel pump without starting the engine, and any will do. I prefer the ‘AFM flap’ method as it also verifies the function of the reed switch in the AFM and the diode pack - and the pump is easily shut off if something goes wrong…
Actually, you can also observe the fuel gauge with ‘left’ and ‘right’ selected in turn. While running the pump there should be no change in either tank’s fuel level. As the gauge is rather crude and slow reacting - several minutes of running is likely required for valid test…
This is a picture through the filler neck (click on the link). The return pipe runs up inside the tank. You can observe the fuel return flow as the pump runs by pushing down the little flap.
I wouldn’t observe the gauges, just observe the return. Also, if you verified proper return you would see a changeover valve malfunction over time, no need to clamp hoses and causing the pump to run hot.
David
Wow so many great answers. I should have no trouble in getting this girl working properly with all this great advise. Great Forum!! Thanks so much. Will let you know when all is well. Am going to drain the left tank also. The right tank stuff that came out looked terrible!! Sloshed it out with gasoline and hope good enough.
chances are not just the fuel has become stale, gummed up or whatever, but that the tanks are also less than pristine from inside. It seems to have become a common opinion on this forum that cheap one way fuel filters before the fuel pumps (for SI and II with two) are good insurance against future malfunction of the pump due to rust flakes pulled in. Paul has posted instructive pics of his SIII setup on various occasions.
FRANK sorry to bother again but when troubleshooting fuel tank
switchover etc, one suggestion is to hold open the AFM flap. I look
in the engine compartment and see a canister lid which is held on by
two clips. But that doesn’t allow you to just pull it out of the way
etc. Where is the filter located? The next round compartment is
connected with a hose with two clamps. I suspect these clamps have
to be removed to be able to get to the AFB flap is that correct?
Where precisely is that flap located? Are there any pictures of
where it is located on this website? Not sure what is the best way
to search for something like that. The only manual I have is a Haynes manual and it
doesn’t cover this area or if it does, it looks entirely different
etc. Was there a Jag repair manual issued that I do not have and
could purchase?
Lee
Lee,
Attached is a picture of an AFM that I removed from one of my parts cars. The flap is circled in red. You have to remove the air cleaner assembly in order to access it.
Attached is a picture of two of the Jaguar documents that are essential to my work on our XJ6s, the Parts Catalogue and Series III Service Manual. Other important documents are green and white owners manuals and the S57 Electrical Guide. I purchased my hard copies on eBay.
