Thread: Lift Pumps 300tdi

On Sunday i had a call from a mate that was replacing a lift pump and needed me to check mine to see which was inlet and which was the outlet. As it is just a simple looking cam driven mechanical pump i cant see any reason why a small low pressure electric pump cant be used in its place ? Another cause for concern i have read somewhere is the fuel lines in/ out of the pump are hard plastic and tend to go brittle and crack and then leak so replacing these with rubber hose is a good start. Tuff RR also just fitted a Delphi filter ( much like a cav) in place of the original, it has a glass bowl and filters are heaps cheaper then OE.

Hi Simon & all,

Haven't been visiting here for a while but I think I can contribute something to this discussion.

The reason you can get away without the lift pump on the 300tdi is not just because it has a high pressure fuel injection pump but because of what else is in that injection pump. The Bosch VE distributor injection pumps all have a low pressure rotary vane pump built into the front of the pump body. This has two purposes: a) to keep the high pressure cylinder positively fed with pressurised fuel free of vapour bubbles and b) to operate the timing mechanism. [The vane pump increases the pressure inside the pump body as rpm increase. This increase in internal pressure works on a piston which rotates the timing ring, advancing the beginning of injection as rpm increase.]

From the horse's mouth (Robert Bosch Technical Instruction): "Normally in the case of passenger cars and light commercial vehicles... the vane-type supply pump in the injection pump is powerful enough to draw fuel from the fuel tank..." but "[where] the difference in height between fuel tank and injection pump is excessive and/or the fuel line between the tank and the pump is too long, a pre-supply pump ["lift pump"] must be installed."

My guess is that LR considered it a border-line case and fitted a lift pump to ensure the injection pump gets a good feed of "pressurised fuel free of vapour bubbles" in all situations, including Defender 130s going up very steep slopes with very cold thick diesel in the middle of a Scottish winter...

This reminds me, I'll have to get back onto making up that lift pump bypass hose set I've been 'gunna' do for ages. I'd also be interested in hearing if any lift-pump-removed vehicles have suffered fuel starvation. Hope this helps.

I'll buy and pay most of that...

however...

if you run out of fuel and try using the vane pump to prime things very very bad things will happen that cost lots and lots of $$$, particulalry if you do it frequently or have bad fuel/filters.

My suggestion is get one of those inline "ticker" fuel pumps and place it inline between the fuel sedimentor (first filter after the tank) and the main lift pump, or bypass the mechanical lift pump entirely.

The best things about these pumps are they are a dime a dozen, generic, have check valves in em so they assist in keeping your fuel in the lines, allow fuel to be pulled through them relatively easily and will prime most fuel systems in about 30 seconds.

There is a relief system in the vane pump in the injector pump housing that will allow you to push fuel past the vane pump to fill the injector housing and flow fuel past it back into the tank.

In a DIRE emergancy if you kill your lift pump and for some reason need to reprime the injector pump try this...

uncouple the return line from the injectors that goes back to the tank... make sure the filler neck is sealed tight ( a peice of inner tube works wonders here) crack all the bleed nuts you can find. Apply gentle (5-6psi max) air pressure to the return line that goes to the tank and as the fuel begins to trickle out of each bleed nut tighten it up. Restore the return line after allowing the tank to vent then try to fire it up.

Hi Dave,

Very good point you make that, if you remove the lift pump, you also remove your priming lever! (Never thought of that, ooops!). I like your idea of the electric 'ticker' backup. What should one of these set you back and where would you suggest looking? Repco?, Supercheap?, wreckers (what models)?

I've never had a need to use the priming lever even when replacing fuel tank, changing fuel filter or replacing lift pump.

Every time it has started straight away. I wouldn't be concerned in loosing it.

get one from super cheap or anywhere else... simply cut the fuel line between the sedimentor and the existing lift pump and install it somewhere in there.

make up a short bypass pipe with some clamps so if the main lift pump clags you can simply slice the lines and install...

Just some clarification please.

If the lift pump fails (usually because of a ruptured diaphragm?) then will the injector pump pull fuel through sufficiently to keep going at reduced speed or do you stop completely?
And if you install a by-pass "ticker" pump, where do you place the pump and connect it to an appropriate (amps?) power supply.

Thanks

One thing to watch is if the pump is leaking internally then diesel will fill the sump and could cause some serious problems - at the least thinning down the oil, the worst igniting. This was a problem on early fords/ holdens etc that had mechanical pumps and were dual fuel and the pumps kept pumping, fixed by installing a small electric pump.