Misfire.

[richyb66]

Ok, not strictly D2 but as it's on my 40V S6 it's close enough for cash.

I've noticed some rough running lately on start-up which is more noticeable when I select Drive. As the car runs on lpg, it only runs on petrol fow maybe a couple of minutes before it switches to lpg and then it runs as smooth as anything.

Last week, as it was still running on petrol, it felt as flat as a fart and the check engine light came on and was flashing. Suspecting it had gone into limp home mode, I switched off, re-started and at almost immediately switched to lpg and ran fine.

Yesterday I used VCDS to get the fault codes and got:

16690 Cyl. 6 burn misfires recognized
16691 Cyl. 7 burn misfires recognized.

which I've now cleared and it's been ok so far. However when driving on lpg, if I switch to petrol, it's still missing slightly and when I switch back to lpg it's fine again.

Based on the symptoms I'm thinking it's fuel injection related. First off I'll probably swap the fuel filter because I'm not sure when it was last done but I'm not sure what to look at next. I can check the resistance of the injectors (if I can get to them) which might indicate a problem and the fact that it runs fine on lpg is steering me away from coil packs or ignition related issues but I don't understand how it can flag a fault code for a fuel induced misfire. Also, is a misfire on two cylinders an indication of something else?