Thread: Lift pump issues, help needed!

Originally Posted by PaulMac

Hi all, I have recently replaced a lift pump on a 300Tdi in a defender.
I'll try and explain the issue I'm having as best as possible.

I had some issues with the car slowing losing power until it eventually came to a stop. I would turn the car off leave it for 15 minutes and it would drive for another 15 minutes then the same deal again. Initial investigation found a hole in the air line running from the pressure side of the turbo to the injector pump. After replacing this it the seemed to be fine for a week or so before the problem arose again.

So next step was the lift pump, I read a lot of guys had similar issues.

After installation the self priming lever would not pump fuel to bleed through the bleed bolt at the top of the fuel filter. I naively didn't think much of it and just kept driving her until at happened again a few tanks later, now the issue has only happened when the tank is at ¼ or lower (greater pressure loss).

I am re-visiting the lift pump for some investigative work. Now what I have discovered is that when the lift pump is coupled up to the fuel lines without being installed to the block it pumps fine, however when installed I get nothing.

Conclusion is that when installed the mechanical actuation arm that sits on the cam is constantly in the up position, there isn't a great deal of stroke on the actuation arm and if it sits only slightly up from its seated position it is useless.

So my questions to the experts is do some models of lift pumps require a spacer, do I have a dodgy pump or is there something nasty happening with the internal cam arrangement?

Sorry about the long spiel, thanks in advance.

You need to rotate the engine crankshaft so that the heel of the cam and not the lobe is facing the lift pump. Only then can you get the full stroke using the manual lever. While the pump is off it is easy to feel in the opening to determine the position of the lobe.

In this position it is also easier to fit the pump to the block.

Thanks john,
So in saying that if you were in need of priming the fuel system would you then need to crank the engine to a position that was on the lower portion of the cam lobe for it to work?

I had some issuses with my 300 TDI Defender.( similar story to yours )
You may find it is a blockage in a fuel line or most likely at the fuel tank
My problem was a bit of rubbish in the tank blocking the pick up pipe.
If there is a suction restriction the primer lever on the lift pump will not return correctly as the pump diaphram is not returning due to the blockage or restriction
A quick solution is to remove the Nylon pipe and fitting of the side of the tank and blow back into the tank.
The same can be done with the fuel line from the lift pump and back to the tank.
I found the lift pump is nothing special and have added a electric (petrol) car type fuel pump just near the tank and a better sediment trap.
This allows bleeding of the injector pump and filter just by turning on the igintion.
The better sedimenter makes life easier for the main fuel filter and lift pump.

There is a updated gasket for lift pumps ERR7339 and is a green gasket. This was brought in because the lift pump was overstroking and failing. this gasket is thicker and should be fitted to stop lift pump failing in the future but I would go with Ron there is a blockage

Thanks for the advice; I will check for blockages tomorrow.
However I coupled the lift pump to the fuel lines but not bolted to the block, and the primer worked fine, telling me that the fuel side of the pump is clear and un-obscured.