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possu · Joined: 29 Dec 2003 Posts: 7

Is it always running when car is running, couse mine is always on and its stop only when i turn power off, can somebody explain me how the fuel pump work normaly.
Thank you

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

It's a pump which displaces fluid by "squeezing" the fluid ahead of a series of rollers as the motor in the pump rotates.

If you mean electrically, how does it work in the car's circuit, try this on. (This is an over-simplification, but I think it's accurate enough for a general overview...)

Turn the key and the relay is energized. It passes electricity to the pump for a few seconds, supposedly enough time for the engine to turn over. Once the motor is running, the relay gets "feedback" from the ignition system letting the car know it is running. As long as the relay gets this feedback, the fuel pump gets electricity. If the engine dies for whatever reason, the relay does not get any feedback and it turns off energy to the pump.
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'79 Eurospec 931

possu · Joined: 29 Dec 2003 Posts: 7

So fuelpump is always on when the car is running? Some cars fuel pump stop when there is enought pressure in system and give more fuel only then when the system needs that.

Lizard · Posted: Fri Jan 30, 2004 9:18 am Post subject:

CMXXXI answer is perfect,

to clear it up though, "whenever the relay is recieving a signal meaning that the car is being supplied with spark, the relays bridge is close passing electrical to the fuel pump, so to answer your question with the greatest simplisity YES
the fuel pump is alway on, although when the pump hits a certain pressure it will turn itself off
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3 928s,

Smoothie · Posted: Fri Jan 30, 2004 9:18 am Post subject:

Don't some earlier models have a switch at the fuel distributor or fuel metering plate that affects power to the pump? I just have a vague recollection of it - not real sure.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

possu · Joined: 29 Dec 2003 Posts: 7

Ok thanks! So i dont have to worry that fuelpump is keeping noice all the time i dont undrestan why the fuelpump relay is so complicated( idont know is that right word) if it has only one job keep fuelpump on when motor is running and stop is when motor is stopped.
Difficult things to me to underestand maybe im just stupid : )

Lizard · Posted: Fri Jan 30, 2004 9:37 am Post subject:

I know what you are speaking of smootie but lets try not to confuse it too much and iirc it was on the 1979 that had that but I could be wrong

as per the comment of the complexity, it needs to be that way, if you are in an accident the engine will stop running if the engine dies, if it was wired in so that it is on with the ign then if you were in an accident and the key was left on your fuel would be pumped out onto the road
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3 928s,

Joes924Racer · Posted: Fri Jan 30, 2004 11:03 am Post subject:

Why does it make alot of noise. The cis (fuel injection system)
needs to be pressurized before itll work. So the fuel pump
turns on.

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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.