SU Fuel Pump (electronic) - air bleed pipes?

(Timothy M Fox) #1

Hello friends,

I have purchased a new electronic SU Fuel Pump to replace the old pump which rather spectacularly failed on my 3.4L MKII. A boot full of fuel and no fire was the miracle. There are some minor physical differences on the black cast section of the pump to my original. As can be seen in the photo it has two pipes which look as though they ought to have rubber pipes fitted to them. What purpose do they serve and do I need to fit rubber pipes to them as the pump is in the boot away from dirt and grime?

Cheers and best wishes,

(Robin O'Connor) #2

No pipes that I am aware of, I think they are equalisation ports.

(Timothy M Fox) #3

Thanks Robin. It’s odd that they are just open to atmosphere?


(Ian) #4

Looking at the fitting at the one by the diaphragm , looks like it is made for a rubber hose to fit on , would it be safety measure in case the diaphragm split’s , a outlet for the fuel , rather then have it traveling inside the pump to the electrics !

(Timothy M Fox) #5

Not sure, Ian? I think it equalises the air pressure in the chamber. The diaphragm on the old pump split and that was a disaster, well potentially!:wink: Perhaps it might be designed to carry away fuel to a safe place outside the car if the diaphragm splits, rather than in the boot, as you say? The air can travel from the pipe closest to the inlet / outlet to the one on the end but not in reverse which I don’t understand. My SU dealer gave me an answer that didn’t sound quite right.

(Ian) #6

That would make sense !

(XJCStu) #7

Had the same question on the other forum. perhaps this will help:

(Rob Reilly) #8

On earlier models like my Mark V and XK120 with the pump mounted under the car on the chassis, there is a hole in the body that points down, so if the diaphragm leaks the fuel will drip on the ground. My XJ12 S2 has 4 of these spouts with hoses on them running out the bottom of the spare tire tray. I would put a hose on it and run it outside the boot.

(Timothy M Fox) #9

Thank you very much for the link. I now understand their function.