Electric fuel pumps on Mechanically injected Diesels

[Maggot4x4]

I have read somewhere that fitting an external electric fuel pump to the fuel line of a mechanically injected diesel can show performance improvements.

Has anyone tried this and is it true or an urban myth?

[abaddonxi]

A few people on the forum have put electric fuel pumps in line on 300tdi engines and fitted a blanking plate over the hole where the lift pump was.

I think this can only be classed as a performance enhancement if your lift pump is stuffed.

Lift pumps aren't the most reliable part of a 300tdi.:D

A few people have also bypassed the lift pump altogether. From what I've read this can possibly lead to fuel starvation at full stick on steep uphills.

The lift pump is there, as I understand it to push the fuel from the tank through the fuel filter, and for the uphills. As it was explained to me, you put the filter on the downhill side of a pump or fuel tank and having the filter in the engine bay means you can't rely on gravity from the fuel tank.

Hmm, to answer my own question. I guess it would be a good idea to shift the fuel filter to the tank if you're going to remove the lift pump.

If you're looking for performance improvement you put it on a dyno and tweak the fuel injection pump.

Ha, sorry, my answer should have been, no idea.

Cheers
Simon.

[JDNSW]

I have read somewhere that fitting an external electric fuel pump to the fuel line of a mechanically injected diesel can show performance improvements.

Has anyone tried this and is it true or an urban myth?

It would be true only if the existing fuel pump was not working properly due to either a fault with the pump or some other problem with the fuel system which the electric pump was able to mask. If operating correectly the fuel lift pump has no impact on performance - it only becomes a factor if it cannot dleiver enough fuel, and no vehicle would be designed like that, although it could happen as the pump ages, although most mechanical lift pumps last well and have plenty of excess capacity.

John

[justinc]

Howdy Ash,

Once the diesel reaches the injector pump in ADEQUATE volume/ pressure then the injector pump is where the real work begins. So, unless the volume and consequently delivery pressure is below spec, then no, it wouldn't make any difference.
I have actually had a 300Tdi running well with a can of diesel on the defender roofrack gravity feeding into the injector pump inlet, I didn't drive it on the road though, so I would only guess that gravity alone would possibly not be enough volume/ pressure to be adequate for pulling up hill under boost, but I must try it one of these days...
I will also add that bleeding the system is very easy with an electric pump, especially on our Isuzu's :mad:as the Tdi will almost bleed itself:)

JC

[abaddonxi]

Howdy Ash,

Once the diesel reaches the injector pump in ADEQUATE volume/ pressure then the injector pump is where the real work begins. So, unless the volume and consequently delivery pressure is below spec, then no, it wouldn't make any difference.
I have actually had a 300Tdi running well with a can of diesel on the defender roofrack gravity feeding into the injector pump inlet, I didn't drive it on the road though, so I would only guess that gravity alone would possibly not be enough volume/ pressure to be adequate for pulling up hill under boost, but I must try it one of these days...
I will also add that bleeding the system is very easy with an electric pump, especially on our Isuzu's :mad:as the Tdi will almost bleed itself:)

JC

I'd say, whatever you do, don't try to prime a 300tdi with the priming lever on the lift pump. That's usually the time that the diaphragm in the lift pump decides to let go and all of your troubles are compounded. A 300tdi will prime itself without outside interference. If it doesn't prime itself I've found that there is some other problem, like having a stuffed lift pump.;)

Cheers
Simon

[rick130]

I'd say, whatever you do, don't try to prime a 300tdi with the priming lever on the lift pump. That's usually the time that the diaphragm in the lift pump decides to let go and all of your troubles are compounded. A 300tdi will prime itself without outside interference. If it doesn't prime itself I've found that there is some other problem, like having a stuffed lift pump.;)

Cheers
Simon

the only problem I have with this often quoted procedure is that a Bosch VE pump isn't cheap (here's me telling Si this :angel:) and they rely on the diesel flowing through them for cooling and lubrication

I reckon a few sacrificed lift pumps are worth an injector pump ;) (and I've only ever changed one lift pump in 220,000km and it was still pumping ok, just weeping a little)

[mcrover]

It is an urban myth on a 300TDI.

You need volume mainly and just enough pressure to push it up to the filter, through the filter and into the injector pump and thats it.

The only advantage to having an electric pump is for priming and if you have just changed the filter then the best solution is to fill the filter first and then fit it and then there is no need to worry about the tiny bit of air that passes through the system.

There are few times you would need to remove injector lines, injectors or completely empty the injector pump and associated lines so they should remain full and air free and if you did have to muck with all these bits, you would have to have checked the condition of your lift pump first and maybe renewed it so a manual pump wouldnt be a problem.

[Bigbjorn]

Diesel engine lift pumps normally supply much more fuel than the injection pump needs to supply the injectors. This is why diesel engines have a return line from the injection pump back to the fuel tank. Other than for priming the system after filter changes etc, there is no point in having an extra fuel pump on the system.