Possible to syphon fuel out?

[spannerrash]

Hi all again.
Sorry to bring this back up again but I just have a couple of questions if anyone can help me out.

Does the fuel pump run constantly when the engine is running?

Does the fuel pump modulate its output at all during periods of low fuel demand?

I realise this is a return (excess fuel) to tank system but it just seems wasteful if the car is running at low load for an extended period of time for the pump to be running at full pelt constantly.

Obviously I could be missing something really fundamental.

Thanks Frank

[MikkiJayne]

Yes, it runs constantly with no clever control strategy. The pressure regulator on the fuel rail adjusts the pressure by bleeding off whatever fuel it doesn't need. Pretty much everything pre-FSI works like this. I would expect the pump load to be fairly constant since its pushing against a constant load of 4 bar. The regulator will adjust flow between the rail or the return.

The C5 RS6 is the only port-injection engine I know of with a PWM-controlled fuel pump. It uses the stock C5 in-tank pump as a lift pump and then has a high-performance pump in-line on the way to the engine.

FSI engines seem to use this PWM method pretty much across the board as far as I know.

[spannerrash]

Thanks once again MJ, much appreciated.