Tearing my hair out with a fuel pump problem.

[yaverland]

Took my partner out in my 1961 MK2 3.4 and she commented on the tick from the fuel pump in the boot to which I confidently replied "its normal and is pumping the fuel from the tank to the engine" mmm no comment on the wonderful sound from the exhaust and the engine. When I got home I noticed that my brand new SU pump AZX 1308 does seem to be ticking more often than normal in fact with the engine not running the pump ticks about once a second. I disconnected the pump outlet and connected a pressure tester and it reads 3.5 psi but the pump continues to tick so the problem seems to be on the input side so any ideas would be appreciated - Alan

[piman]

Hello Yaverland,

when the pump internal pressure equals the diaphragm spring pressure it stops pumping. If there is a leak on the inlet or outlet then the prssure drops and the pump starts to pump again. By putting a pressure gauge on the outlet with no leaks (i presume) then there must be a small leak in the suction which is or should be the one way suction inlet valve, possibly due to dirt. this lets the pressure drop as fuel returns down the suction line.
While not correct the amount seems to be very slight and it's your choice to accept things as they are or look at the possibility of dirty fuel?

Alec

[J44EAG]

I fully agree with Alec.

I once saw a similar issue in 1972 on a brand new Triumph 2000 albeit with a manual engine lift pump. The car had covered just 42 miles after ex-works delivery and spluttered to a halt with fuel starvation. The inlet poppet valve was not closing properly. The fix carried out by a garage en route to our destination was to swap out an old pump from a wrecker they had around the back of the garage. That installed, off we went again. The pump was later replaced under warranty but my Father always kept that old second-hand pump and a half inch spanner in the boot after that.

Sometimes even new parts are defective. Just one of those things.

Mike K

[yaverland]

Thanks for the replies,

I got out the old original pump which was not working at all, found the points were very badly pitted and corroded but after a bit of grinding and sanding fitted it temporarily and guess what it stops ticking once the carb float chambers are full (and the ticking of the old pump is much quieter). So it looks like a pump issue. Its an interesting thought though about dirty fuel as my car is an early model there doesn't appear to be much in the way of fuel filters. - Alan