Car: Audi S5 2008

I have a problem in my car where sometimes my car will be hard to start after driven for a while. Normally if I floor it close to where I stop the car, it's harder to start. When I took off the inlet air hose, I could smell petrol (after being shut off overnight).

The car doesn't have a problem starting when cold, so I'm suspecting that the fuel is slowly leaking into the cylinder. The car is a direct injection engine, so fuel does not enter the intake ports.

My question is, when the fuel system is shut off under high pressure and the car is hard to start afterwards, does this usually mean fuel is leaking into cylinder via the nozzle of the injector, or around the seals of the injector?


1 Answer 1


I fear you may have jumped several steps at once here. It is likely that a failed or faulty coolant temperature sensor is causing your hot-start issue.

As regards the fuel system, this will retain pressure for some time after the vehicle is stopped but the pressure in the fuel lines typically remains fairly constant as it's set by the fuel pump and governed by the fuel pressure regulator. If anything, the fuel pressure at full throttle could be seen to be lower because the demands from the fuel rail and injectors would be greater.

  • 1
    Funny you say that, as I've noticed the radiator fan running really loud lately (albeit middle of summer), for extended times. Could you please explain how temperature sensor causes that to happen?
    – tgun926
    Commented Jan 5, 2017 at 12:35

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