SFD732

Thank everyone for the replies


Car ran great under load or at idle prior to it misfiring on the 1 bank. The only issue ever was a bad hot start maybe 3 times but not when whatever is going on now happened.

car has had in the last 5k

oil strainer
pcv/oil separator
hpfp on bank with misfires

Just checked turbo, fins look good, no scoring, spins freely

going to disconnect front O2

Then plugs
Then try switching cam sensors?
prob can check cam positions via vcds. Will have to find procedure

MP4.2+6.0

Not sure cam sensor would be productive. Been a long time since I looked at carefully, but even in D3 era (W12 for me) those were cross checked in a self test mode along with crank sensor. In relaxed drives (low loads steady speed IIRC) warmed up, ECU would periodically run a check behind the scenes of the cam and crank sensors. In turn it is what spits out a CEL eventually if something goes wrong. Had two failures of exhaust cam sensors in D3 W12--exhaust would cook them---where I delved into it more. And then likewise, it's a direct code pointing at a specific sensor. For yours if you get to point of thinking of checking them, maybe first review the 4.0T SSP (Self Study Program) document for theory of operation.

A8L_New_England

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Just spitballin'. What sensor or system might be good to look at, which hasn't been mentioned and would cause misfires on one whole bank?
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SFD732

It doesn’t make much sense. I would assume the root issue is a sensor but why no codes.

would driving the car 2 miles home with let’s say a stuck injector cause too much fuel to get forced through the other injectors cause a lean condition on 1 cylinder and rich on the others? Possibly compounded by trying to diagnose and letting motor run for periods of time while running diagnostics?

I really need to pull plugs and have a look at them, that should tell me if there is a lean/rich condition and let me drop a scope into the cylinders. Though there are not really any bad noises while running so I assume no valves into pistons or broken plugs

I don’t have the logs but I swear it was only 2 cylinders showing misfiring initially (car has been sitting since early November)

Also I work 24 hours tomorrow and then leave for a hockey tournament in Boston Thursday evening so there might not be any progress with this until next week.

kelisko

I'd say not. I had similar misfires on my 3.2 V6 and it turned out that all three "new" plugs on the same bank were killed.

You should.

Check out my video below to see what happened to my spark plugs.

A8L_New_England

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Not remotely the same situation. You removed your cats and repeatedly over-revved your engine with "new" plugs... This guy just went for a short ride to the grocery store with old plugs.
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You likely had under-torqued the plugs upon installation, and they failed due to inadequate heat transfer and detonation.
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That said, it would certainly be worth looking at / swapping his plugs, as they may yield some clues.
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MP4.2+6.0

Faulty sensor that READS the purported misfires--a knock sensor itself... Corner fluke case as another, wiring harness issue on way to coil packs on that side. That kind of fluke might follow prior work that damaged it somehow. More likely perhaps, even w oil separator/PCV work done already, maybe a mechanics mistake breaking or connecting something leading to a vacuum leak on that side. Dealer did my S8 one in recent months and I have never done any work in that V area, so not sure hands on how things actually bolt and connect up. So, a variety of things.

Pre cat O2 on that side/bank is still probably lowest hanging fruit while we debate how many arm chair mechanics does it take to guess the issue. Especially clearly having lost one on my 2015 S8 pe-60K miles. Did them all just to be done w/ it (pre and post O2 connectors are mixed among banks in a non intuitive way because of hot V set up and near 180 degree turn header/downpipe takes right after turbos--almost have to see it do understand why). So once you do pre and post on one bank, just parts cost basically to do other bank (B1S1 is grouped with B2S2, and B2S1 is with B1S2 for where connector plug ends are physically). More surgical is to just do one pre cat on the B1S1 side throwing the code since pre cat failure is the more common. One side is very easy where grouped connectors are high up in plain sight near ABS unit IIRC, other side is major bitch with connectors down above inner halfshaft CV joint on passenger side in a quasi blind and tight reach underneath. I forget which side of engine compartment has the B1S1 connector end point--easy to look under engine trim cover to se turbo area and trace the O2 cord. I didn't touch coils or plugs or anything fuel or air on mine. 100% fixed it. Now at 35K on current plugs and I will do them along with air filters at next oil change in a few months as a "major" service.

SFD732

turbo looks good. Replaced plugs on problem side today. Fault codes went to only cylinders 3 and 4. I am ordering coil packs and replacing plugs and all coil packs on both banks. Unless someone thinks I should go a different direction

MP4.2+6.0

Still O2...

Three of your four plugs in picture look like they may be running rich actually. Only second one down has the classic best look--dry, light tan. Of course misfire is usually associated with lean run, not rich. But if O2 is sending a faulty read out to ECU more generally, who knows. Enough signs in here for me to change it given modest cost if you get Bosch OES (non-dealer)--a few coil packs worth.

SFD732

I will do coil packs and o2 sensors. It is def running rich, can smell it while running