Audi S5 V8 4.2l (CAUA): fuel return line

[Silv3r]

Hello,

Is it possible that the S5 with V8 (2008-2011) has no fuel return line to the fuel tank?

It looks like there are three lines from the fuel pump/tank only:

1. Fuel line
2. Breather line
3. Vaccum line

Wysłane z mojego SM-G950F przy użyciu Tapatalka

[b7_Andy]

That is correct, Audi doesn’t not use a return fuel system in the B8 S5, it uses a high pressure fuel system where instead of the low pressure fuel pump running at constant 12V supplying the engine with constant fuel, it is controlled by a fuel controller above the tank and runs at varying voltages to send only the exact amount of fuel needed to the fuel rail... the fuel is then pressurized again at the fuel rail by the two high pressure fuel pumps before it is injected directly into the cylinders (not the manifold). I believe there is also some sort of pressure regulation in the filter for the low pressure fuel pump (at least it’s like that in the B7 direct inject systems). And I think in the S5 the fuel filter is located in the fuel tank.

[Silv3r]

Thanks!
Ok so... if I deactivate the fuel pump in a tank (by fuse) and put the main supply line to a can with a chemistry (injectors cleaner), do the hight pressure pumps suck the cleaner?

Wysłane z mojego SM-G950F przy użyciu Tapatalka

[b7_Andy]

Thanks!
Ok so... if I deactivate the fuel pump in a tank (by fuse) and put the main supply line to a can with a chemistry (injectors cleaner), do the hight pressure pumps suck the cleaner?

Wysłane z mojego SM-G950F przy użyciu Tapatalka

I don’t know how well that would work. The car definitely wouldn’t run like that and with no signal from the low pressure fuel pump it would probably just keep the injectors closed and I don’t think the high pressure pumps would move any fuel.

[Silv3r]

Any1 else with the answer?

The question is:

If the mentioned two HPFP are able to pump/suck the cleaner from the can or the cleaner have to be applied under some pressure to the HPFP?

I want to give a chance for Tec-2000 before replace the injectors :)

[dymx]

This is like ancient, but searching up on my fuel filter/pump issues. The injectors can be cleaned by a shop for about $8-12 per injector. I did this for mine and I would highly recommend it. I did it after purchasing the car second hand, and 2 of the injectors were clogged.