Lean running & occasional misfires

5.2 V10 40v Naturally Aspirated - 429bhp
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barryrs
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Joined: Fri Jan 20, 2012 1:26 pm

Lean running & occasional misfires

Post by barryrs » Tue Aug 19, 2014 3:16 pm

Just a quick note to let anyone suffering from the above faults what my fix was as there's so little info out there on the S6.

I had faults come up for lean running and occasional misfires on pretty much every cylinder on both banks and set about tracing the problem.

A bit of searching around lead me to believe that it was a vacuum related and this can be checked fairly easily buy trying to remove the oil filler cap or dip stick with the engine running.

Example here - https://www.youtube.com/watch?v=cLSEgGtMatk

Knowing that the crankcase pressure was too high i began to look for the culprit with the following 2 options being the best bet after checking everything on top of the engine.

1. vent pipe with check valve - 07L 103 217 B circa £40
2. oil separator incorporating two-stage regulator - 079 103 464 D circa £135

The vent pipe is a bit of a nightmare as the entire inlet manifold has to come off to access it so i decided to try the oil separator first and thankfully this was the problem.

Upon removal (which is fiddly but not too difficult if you whip the throttle bodies off) we discovered that the spring operated piston over the cyclones was jammed in and you could blow back into the separator from the oil return pipe.

A swap over and reassembly has the car running smooth again and no faults being thrown up.
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