Update

So got wrapped at work for a few days so finally test drove the car on a few trips and the following are results:
1. Misfire is not present with engine warming up. When engine temperature is mid scale / normal. The misfires are now:
- 000768 random multiple cylinder misfire detected P0300-008
- 000769 Cylinder 1 P0301-008 Misfire detected.
- 000774 Cylinder 6 P0306-008 Misfire detected.
- 000777 Cylinder 9 P0309-008nMisfire detected.
I also have the MIL back on and the New fault;
004229 - Mixture regulation bank 4, range 1. P1085-004 Lean limit exceeded. MIL on.

I checked VCDS Readyness and the secondary air has not passed.. can this be connected?
this seems odd as replaced both vacuum valves and blower a year ago and this was ok... I’ll have to remove wheel liner and check all pipes intact etc...

Based on the above I’m thinking a possible fuelling issue or vacuum leak (?) or possible dreaded inlet manifold flaps issue. Thinking about looking into fuel trims to hopefully shed some light...

Really odd as the engine has no misfires, running smooth when warming up.....

Any thoughts or guidance would be greatly appreciated.

Thanks

Bank 4?, it's not W12, you only have 2 banks on V10. But it does sound like not enough fuel, possibly cylinder 6 or 9 not getting enough fuel so (check, swap, replace those 2 injectors). Or maybe not enough fuel in general ( fuel fiter, pump)

I noticed that 'bank 4' too. I wonder if, from an electronic point of view, its treating it as two V5s, or a V4 and V6? It probably has two ECUs like most of the larger FSI engines so that could be where it comes from. Bank 4 in theory could be 7,8,9 or just 8,9 depending on how it's arranged.

I would go with injector too. I did read on another forum that a member on Pistonheads bought a S8 V10 with a misfire and it turned out to be a faulty injector

post #4

https://audisrs.com/v10-misfire-t63354.html

Thanks guys for your suggestions. The v10 has 2x ECU’s and 4 banks.

I’m hoping to figure out how to read the fuel trim on VCDS hopefully understanding this will point the way to diagnosing the issue - it’s really frustrating when considering I did the carbon clean only weeks ago, the car then passed its MOT just fine then deteriorated ....

I think the miltek system contributed greatly to the three points on my licence - the noise of great and makes it hard to have your thoughts elsewhere😊
My only regret-ish is that it does drone a bit at motorway speed 1000rpm-1200rpm...

Hi guys,

Update - connected VCDS and monitored fuel trim so bank 4 (cyl9 and cyl10) is measuring way out with long term fuel trim up to 25 fluctuating between 23 and 25... I believe this should be below 10 as on the other banks...

I did clamp off vacuum pipes and doused a whole can of carb spray around the inlet manifold, breather and various vac pipes - no change in fuel trim readings.

Interestingly I pilled dipstick and change in readings as expected. Couldn’t even remove the oil filler cap - hadn’t realised the vacuum was so extreme at idle...

With the other 3x banks fine the problem looks localised so I’m guessing not a vacuum leak as that would likely affect more banks since this engine although two throttle bodies has a common inlet manifold chamber.

Figuring this means a mixture problem so either an ignition / injection / compression problem on 9 and 10.

Anyone have deeper understanding of VCDS as I’m sure there must be other parameters that will help focus on the actual fault?

Thanks guys for any ideas.... time for a cuppa.

Trim should be within max 12.5% (really within 3-4%) and somewhat equal on all banks, looks like cylinder 9 has a problem, injector most likely. You could swap it around with another cylinder to confirm.

Thanks Ainarssems,
I’m dreading taking off the inlet manifold again... so just want to diagnose as best I can before taking things off again.
In thinking about the high vacuum I’m getting at idle where I cannot even remove the oil cover - any chance you can check your oil cap and let me know if it is easy to remove at idle?

I’m considering that I may have a defective PCV/Crankcase breather-oil separator valve. This would actually make some sense as it is located at the back of the engine near bank-4.

Thanks,

To check this better I am considering the propane test, adding propane to the inlet manifold to richen the mixture. If the fuel trim is driven rich on bank 4 then this should more conclusively point to an injector issue (surely). If not and bank 4 still reports a lean fuel trim then it should be that defective 02 sensor.. any thoughts?

Thanks,