mgrover, it sounds like you're talking about the adaptive fuel trims in SDD, yes? If so, can you post a picture of your table? This is the best diagnostic tool for fueling faults on these.

The post-cat sensors on these do also control fueling, in the adaptive fuel trim display this is called sub-feedback trim.

Unfortunately I don't have ssd but just a bog standard bt adapter. Am tempted to just purchase a gap idd tool though

The iidtool is fantastic, but I don't think it will show the adaptive trim tables, I've only ever seen that on SDD.

It looks like you took care of all the 'normal' stuff already, the adaptive trims will tell you exactly where it's going lean. Standard fuel trims that you see on a display don't tell the whole story on these.

The only thing I see missing on your list of common issues for lean codes is spark plugs. When they 'wear' down, you get incomplete combustion, which will shift trims lean, and sub-feedback rich under load.

What brand MAFS did you install? I've had issues with all but Denso.

Hi rover guy just going to hijack for a minute as you seem to know your stuff.

As you can see I went through a similar process and now in a fairly good place - from running both banks lean 15-20% changing the maf, both precat sensors and all damaged gaskets and pipes on a smoke test I actually now have it running rich at around 5 percent on each bank occasionally spoking as high as 10% - I didn’t do the post cat sensors could these cause this? I am not overly worried at those numbers unless I’m told otherwise but if it’s could be a fix I’d do them, I didn’t realise they controlled the trims too. Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

Dan, don't worry about spikes when you're looking at live data, your trims should move around as you drive, it's a balance between short, long and sub-feedback trims. If you're only looking at one, you're not getting the full picture.

This is why the adaptive trim table is so important.

Dan, post cat sensors just check the efficiency of the cats, they have no effect on fuel trims..  Pete

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Haylands, that really isn't true for these engine management systems (page 11 has a better description than I'll make) but was correct for earlier systems.

I haven't read through that document in years now, but I remember something in it being worded very deceptively, so don't follow it's process to the t. This relates only to the Denso EMS setup of the 4.4/4.2, but does also apply to the Denso 5.0 up to 2013/14.

**Edit: can only images be uploaded here?
Screenshot of document attached.

May be worth getting some downstream ones then as I’ve done upstream Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

Probably won't be the DS sensors at fault, since they're regular O2 sensors, it would normally throw a sensor fault before a fueling fault.

Do you know what brand MAFS you put on?

Everything is denso - it’s just running slightly rich most of the time as I say its only a couple of percent maybe that’s just ages as it drives great with no faults - maybe I’m looking into it too much just wondered if changing those two would get it bang on Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

roverguy7 wrote:

Probably won't be the DS sensors at fault, since they're regular O2 sensors, it would normally throw a sensor fault before a fueling fault.

Do you know what brand MAFS you put on?

ive got crap maf replacement tbh given a denso is like 80 quid

I'm in the US, but can usually find the Denso sensor for cheaper than that, Denso PN 197-6020 is what to look for. There's also a chance that the rest of the work might have taken care of the initial issue, and a cheap MAFS is at fault now (again, slightly shooting in the dark here without an adaptive trim table) But, if you still have the original MAFS, might be worth tossing it back on and seeing what happens?

Dan, if you're not getting any faults or drivability issues, let it be. These systems are always adjusting, and seeing the numbers fluctuate is not a problem. These things do tend to run richer than I'd like to see, but it's a non-EGR system with not the best design when it comes to keeping charge air temps reasonable, so extra fuel is necessary to a point.

The new maf has only been on two weeks max. Realistically I need a definitive way to reset the adaptations. So tempted to drop cash on the iid tool

i checked my idle ltft and short term, at worst it was 6% which seems pretty good. i just need to find the issue in the rest of the rev range.

bit of an update. my trims at idle are actually decent, they used to be really crap, but my trims are 2.5k-3k are like 20%

Get a maf why don’t you message rob at duckworths on here and get a price with the forum discount Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF