Audi Rs6 c6 Cranking issue

[AreckiRS6]

Hi All,

Has anyone experienced a cranking problem on their RS6 V10 ?? When my car reaches operational temperature and left for a while i cant start it properly. Sometimes takes me 3 times to start the engine and it happens from time to time. Noticed that also sometimes after starting its going straight away to 3000 revs and dropping down. Once stared i can switch on and off without a problem. Fuel related issue ?

Appreciate for any hints
Eric

[Jim Haseltine]

Does it start ok from cold and just plays up when warm?
Can't comment on the RS6 but on previous FI vehicles I've known this happen on cold starts if the fuel line pressure isn't retained when the engine stops. With one I could leave it for a short while like up to a couple of hours and it'd start ok but any longer (like overnight) and it'd take ages to fire up. The RS doesn't have a pressure accumulator as far as I'm aware but the filter has a pressure regulator which might also have a non-return function.
But (and this is something of a guess) if it's warm starts where you have the problem the high revs you get sometimes sort of suggests to me that you might have leaking injectors.
In both cases though I'd expect the either the pre or post pump pressure sensors to complain.

[welwynnick]

This sort of thing sounds like fuel vapourisation due to the high ambient temperature under bonnet. This is usually avoided with the pressure regulator that retains pressure after shut down, but if the regulator leaks, the pressure may drop and the fuel may "air-lock". I'm not so familiar with HP fuel systems, and part of the answer may be about where the problem is - in the LP or HP part of the system.

One of the work arounds with a hot start may be to turn the ignition on and off a few times before cranking. The LPFP will probably switch on for a second or so each time and charge the system. If that works I would change the LP fuel pressure regulator. If it doesn't, I would look at the HP system as Jim describes.

Nick

[AreckiRS6]

Jim, Welwynnick

Thanks for your answers.
Jim yes this just happens to me from time to time when i turn the car off on operational temperature and trying to start it after approx half an hour. It does crank as it should but it feels like its not getting enough fuel. No problem when starting on cold and once started i can switch off and on without a problem. Tried to scan for faults but my diagnostic tool is not reading anything. Think i will get VCDS.