bosch fuel supply question

[d-jimbo]

ive got a bosch pump which has been losing prime and leaking a bit of diesel. i cant see where this is coming from but i know it is the pump cos i can hear air escaping when i prime it. i'm going to be replacing the seals which can be got at without taking the pump off (havent got time to do them all at the min). however, i fitted an electric fuel pump to prime it for me in the meantime (wired up to glowplug relay). i'm going to be fitting a fuel pressure gauge and thinking of wiring up the electric fuel pump differently so that it is on all the time. my questions are as follows:

1)what should the internal pump pressure be? (wil 5psi be ok)

2)where are the usual places for an injection pump to be leaking from?

[d-jimbo]

when i say internal pump pressure i mean pump inlet pressure. i think i'm just gonna wire the pump up to a switch inside the car and run it for priming until i get the seals replaced and then try running it whilst driving to see if it makes any difference.

[Dan!]

The pump has no pressure at the inlet as the pump sucks the fuel in, so essentially its a vacuum at the inlet. Only once inside the pump is there positive pressure

[d-jimbo]

ah, so no pump in the tank then... do u reckon what i'm gonna do will be ok?

[Dan!]

From what I understand, applying any pressure to the inlet of the pump will totally mess up the stock advance system, which will result in poor running. Some people have made low pressure pumps work, but its not the sort of thing you can just stick onto a stock pump and expect to work normally.

[d-jimbo]

it is only a low pressure one. i stuck it on to just prime the pump with but since doing so, the power seems to die off at around 3.5krpm. the only thing different with the pump switched off is a slight added resistance to the fuel inlet. this led me to think that the pump cant get enough fuel. its not quite a stock pump, it running more fuel and more lda travel. the pump is only 5psi so i'm hoping it wont really affect the timing?

[mark_airey]

You also need to consider if the little lift pump your using can flow as much fuel as the VE otherwise you will restrict the pump and make it worse!

Best idea would be to feed a swirl pot in the engine bay using a lift pump and let the injector pump suck from that

[Ruan]

Remember, a Bosch VE sucks WAY more than it needs due to the advance mechanism and the fact it uses the excess diesel for cooling and lubrication... Hence if you shove pressure at the pump inlet you'll mess with the advance curve... 99% of lift pumps don't supply anywhere NEAR the fuel flow required, you need sorta drag car spec lift pumps to get it working properly.

With regards to the leak, leakoff pipes from the injectors, hand primer...

[Poodle]

I hadn't realised the leak-off pipes could allow air ingress in a way that would empty the whole system..! Something else to replace. :roll:

[d-jimbo]

ok, thanks for the info. i've replaced the fuel lines with some fancy clear ones. when i turn the engine off bubbles come out of the pump fuel return. i guess this could mean its the leak off lines? i'm gonna be replacing them with clear jobbies too.

[d-jimbo]

ok, so i replaced the leakoff lines with clear ones and it doesnt seem to be these leaking. i think that its the fuel return banjo. would i be best off just replacing it?

[Poodle]

Sure it's not the crush washers around the banjo..?

[zx_volcane]

ok, so i replaced the leakoff lines with clear ones and it doesnt seem to be these leaking. i think that its the fuel return banjo. would i be best off just replacing it?

where you getting all this clear line from?

[d-jimbo]

yeah i think it could well be the crush washers. the clear line is an ebay find.

[Poodle]

Can get a genuine seal kit for these for £13+vat, may as well for that money.

[d-jimbo]

yeah, ive got one now. it looks like thats the next thing to do, i was just trying to make sure it wasnt anything else before i start pulling it apart.