Cold start

[c3nturi0n]

Hi all,

And hope you are keeping nice and safe.

Here is what i noticed the other day on cold start. I did check VCDS for any obvious issues and nothing evident was flagged in the system.
https://www.youtube.com/watch?v=M3vZsmC ... e=youtu.be

Has anyone experienced anything similar or have suggestions what it could be related to?


Rgds


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[cammmy]

I haven't seen it from outside but mine stumbles a little shortly after startup. It smooths out pretty quickly.

Looks and sounds like a misfire, though it could be any number of things causing it. Are we able to get readings from the o2 sensors with VCDS? A misfire would show up as a lean spike, since so much air is making it through to the exhaust. That would be relying on the sensors being heated units, and allowing the car to sit with the ignition on but not started for a bit, as o2 sensors don't work when cold.

[c3nturi0n]

interesting observations. Thanks Cammy.

It’s also worth knowing that if i was to delete errors under the OBD menu (albeit none were present) the car would run significantly better. That usually last couple days and then it’s back to this slight ‘misfire’ like phenomenon.

Here is something i also picked up in VCDS.

Note my car is on Stage II with non-res exhaust fitted to it so some of the items in red below may as well be considered ‘normal’ .




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[cammmy]

Hmmm, is there a way for you to get more info on that o2 failed or incomplete?

I have a secondary decat and the same software, I'll try remember to take a reading as I need to reset the service due reminder anyway

[c3nturi0n]

Cheers.

I’m not that versed with VCDS bit if there is a way to pull additional data i can certainly take a look at it later?

Thx again!


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[c3nturi0n]

Morning gents... has anyone had a chance to look into this for me?

Any assistance would be greatly appreciated.

Thx


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[IanH755]

It looks like a misfire in the video (small puff of smoke + hesitation) so you could check VCDS groups 15-19 for the misfire counters (only 3 cylinders per group so all 4 groups needed) when the engine is running a cold start. If the misfire is intermittent enough it won't put the EML on as it has to pass a threshold of "total number of misfires vs time" before it will put the EML on.

Best case it confirms if it is/isn't a misfire which helps with further fault finding.

[cammmy]

I had a look at mine yesterday and didn't see any of those errors you pictured.

[c3nturi0n]

It looks like a misfire in the video (small puff of smoke + hesitation) so you could check VCDS groups 15-19 for the misfire counters (only 3 cylinders per group so all 4 groups needed) when the engine is running a cold start. If the misfire is intermittent enough it won't put the EML on as it has to pass a threshold of "total number of misfires vs time" before it will put the EML on.

Best case it confirms if it is/isn't a misfire which helps with further fault finding.

cheers Ian.

Re where to run the log/graph, would that be under OBD menu or Engine I/II?

[IanH755]

In Engine 1 click on "Meas. Blocks -08" (IGNORE THE RED ARROW)-



Which displays a screen like this, where you type in the group number OR use Up/Down selections to view each "group" (so use Up to select "15" to see cylinders 1-3 misfire) -



As there is only 3 groups per page and 3 cylinders per group you can only view 9 cylinders at one time so it'll take 2 cold starts to view all 10 cylinders.

EDIT - One thing I can't remember for sure - I know group 15 is definitely Cylinder 1-3 Misfire but, even though VCDS says "Group 15-19" is the misfire section but that is for a "Standardised" ECU. You may end up having to click though ALL the groups to find all four "misfire" pages as the group numbers are not "set in stone" for some unknown reason and from what I've seen the RS6 ECU's have things scattered about, so you might end up with Group 15, 27, 66 and 92 for example. I've no idea why it's been made so difficult!

Found a YT video of someone doing Misfire detection on a 4.2 A6 (same procedure) - see how their Misfire groups aren't 15-19 like VCDS says it is!

https://www.youtube.com/watch?v=2fyUyXgJMtY

[c3nturi0n]

Cheers Ian - much appreciated.

I did go through the instructions and for me those values sit at 207-209. According to VCDS they all show 0 value (see below).

What’s interesting is that while misfire like symptoms are more prominent at cold start, when it warms up it does get better (albeit i feel that the car ever so slightly shakes and it isn’t quite right).

I also went all the way from 209 to 254 and there are some other properties / values captured under the ‘Count’ menu. Those do indeed have non zero values (but worth noting that neither value changed while the car was running to indicate a misfire for instance).




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[IanH755]

That looks very different to the screen I had (mine was group 15 to start with) - Here is a still from my "broken engine" video on YT

[c3nturi0n]

Thanks.

Interesting to note that on a fairly dated version of VCDS i have (12.12) there are no fields labelled Misfire. I also checked Engine ii and it pretty much mimics options that are available under Engine i.

I’ll give it a go one more time tomorrow to see if anything obvious comes up.

Ps. Any other avenues worth exploring at this stage?


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[IanH755]

Interesting to note that on a fairly dated version of VCDS i have (12.12) there are no fields labelled Misfire.

Ah, mine is 18.9.1 which may explain the difference.

[c3nturi0n]

Not much luck with VCDS re misfire.


Any other avenues i could explore?


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