This pipe slots into a feeder pipe in the bracket half way up the side of the tank - which runs down to the bottom of the tank. (Marked 2)
When the tank goes under 1/4 full, this joint is no longer submerged and air can be drawn in through the buggered O-Ring. I'm gonna hit the nearest dealer to get the exact part required, diesel resistant and all, as it'll only cost a few pence and be the exact fit.
While I was under there, I stuck the multimeter across the pump terminals and discovered that the pump itself is good. Fires up correctly, but I think it might be worn to it's servicable limit, as if you look carefully at the above picture you can see metal shavings in the bottom of the tank right under where the pump entrance is positioned.
I'll replace both parts
If you've got a diesel and there's air in the line I suggest you change that O-ring and see what happens. The car is now starting a lot better from just having disturbed the pump and reseated the o-ring.
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