[Dustydogs]

Hi All,
First time post but calling out to any wizards looking for a trouble shooting challenge! sorry for the essay.

My car is suffering from a constant cylinder 6 misfire after replacing the valve cover & gasket, new index 12 injectors and ngk sparks plugs gapped at 0.22.
At each attempt, idle is really rough and running very rich, cyl 6 spark plug is usually wet and most others are black, moreso on bank 2. There's a good amount of white smoke out the right pipe.
I get no codes until I hold the revs above 3k for awhile then I'll usually get a misfire code on 6cyl, sometimes on 5cyl as well. HPFP code has shown but only on first start before fuel is properly primed, then it doesn't show again.

So far my attempts to fix have been:

- Re-installing the old injectors, no change
- Double checked Injector couplers & seals, they insert quite easily but don't move when retained.
- Swapping coils, nothing - consistent cylinder 6 misfire code
- Swapping injectors around - same ( I know seals should be replaced every time they're removed but they're still good on the new set at least and it should at least idle correctly if this was the issue)
- Re-installing the old Valve cover with new gasket, no change
- Swapping 10k old Bosch spark plugs with new NGK's, no change
- Checked vacuum pressure and all is good
- Checked all wiring and sure I haven't missed anything, grounds are cleaned and good.

The car was running well except for the occasional super knock code at WOT which led me to change the index 10 injectors for the index 12 in the first place. There was also a slight oil weep around the rear of the old valve cover so I changed the whole cover and gasket as preventative measure.

The car is an 07 e90 auto with 140k miles (220k kms) on MHD 1+ 7.1 tune. Has VRSF charge pipe & FMIC, stock down pipes, replaced stock turbo's with same but upgraded to silicon inlets (while I was in there) and all other maintenance is done including HPFP a while ago. It's been well maintained and not driven too hard. mostly.

Battery is a little flat, I'm about to change but not sure that's the cause.

I'm leaning towards swapping out the 4-6cyl pre-cat 02 sensor but before I go swapping out more parts, thought I'd check with you guys for thoughts before I do.

[Dustydogs]

Forgot to add, intake valves were blasted 12 months ago.

[zomski101]

Did you code the injectors?

[Dustydogs]

Yes - forgot to mention that, thanks

[BM3Rrrr]

Sounds like one or more leaking injectors, you said cyl 6 plug is wet most of the time. Wet with fuel or oil?

[Dustydogs]

Wet with fuel but the problem is I've tried 3 different injectors in cyl 6. 1 of the old index 10's, and 2 different index 12's which were swapped about into other cylinders and didn't wet the plugs any more. It's only cylinder 6 that is wet with fuel.

[Dustydogs]

Just to close this out - it was the injectors as suggested. I'd assumed because I put the original set back in and it still ran rough that the problem was elsewhere but it must've just had too much unburnt fuel through the system.

[Soden82]

Good to hear you figured it out. I have persistent cylinder 6 misfires. Putting new index 12 injectors in either tomorrow or next Sunday. Hoping this solves the issue as I did all of your above maintenance prior