2.0 TFSI strange misfire at low rpm when cold

[turdzi]

Hi there.

Maby somebody here has experiaced something similar.My 2011 B8 2.0 TFSI 211 developed strange misfire / fuel cut under 2000 rpm when engine is cold. I own the car from new I has tune on it and I has around 75kkm on the clock.
I have changed spark plugs and recently coils without any affect.It is really strange , for me it seems more like fuel has been cut off on all four cylinders for second or to.After engine get some temperature it runs perfectly.
It's often take place after night.VAG doesn't show any codes , no check engine.
Any ideas ?

[jorte014]

Had that exact problem, only happened when cold, around 2000-3000 rpm the engine had a hard seize, turned out to be the SPULEN under drive pulleys that were installed. Removing them and going back to stock fixed it for me.

[van462]

May want to have the battery checked. The combination of cold and night (headlights running), plus heated seats, front defroster, rear window defroster may be causing a voltage drop. Just a guess but low voltage can do strange things.

[chawaba]

Mine is having the same exact problem after I had the K04 stage 2 turbo upgrade for B8.5. Sent APR an email of my problem and still waiting for a response.

[S4'ed]

Carbon build-up on intake valves?

[turdzi]

Had that exact problem, only happened when cold, around 2000-3000 rpm the engine had a hard seize, turned out to be the SPULEN under drive pulleys that were installed. Removing them and going back to stock fixed it for me.

I'm not sure what do you men by aftermarket spulen under pulleys ? However apart from sports cat , IC and tune everything is stock on the car so no aftermarket addons/parts apart from tune can be blamed.On the other hand I flushed ECU at 10 kkm at least 3 years ago so if it wasn't bug in the tune I would come much earlier ?

[Mike@PureMS]

Carbon build-up on intake valves?

Most common symptom we see is cold start misfires when there's a carbon buildup problem. Would be my first place to look as well.

[jorte014]

I'm not sure what do you men by aftermarket spulen under pulleys ? However apart from sports cat , IC and tune everything is stock on the car so no aftermarket addons/parts apart from tune can be blamed.On the other hand I flushed ECU at 10 kkm at least 3 years ago so if it wasn't bug in the tune I would come much earlier ?

This is what I meant: http://www.uspmotorsports.com/Audi--...y-Kit-SSP.html

That's for a VW, however the ones for our cars look similar.

[turdzi]

I see but I don't know how pulleys can affect ignition ?

[turdzi]

Most common symptom we see is cold start misfires when there's a carbon buildup problem. Would be my first place to look as well.

Well that's not exactly what I wanted to hear :)
I know that carbon buildup can be a problem in N/A engines even after 30 kkm but I thought that on turbo engines it takes at least 100kkm before it becomes to be a problem.
I think I will start with that what its cheapest ant easiest though give battery new life ;)

[jorte014]

I see but I don't know how pulleys can affect ignition ?

It weakens and wears out the alternator messing with the electrical system. I've had 2 other cars where i've swapped out the pulleys and the problems were almost the same. That's why I kind of had an intuition on where to start diagnosing. That being said, this is my first Euro car and the most sophisticated out of all the cars i've owned (turbocharged, direct injection, complex ECU etc). You said you don't have the pulleys, so it might have been a problem just isolated to my situation. If I had to take a guess, I agree with the other post that said it's the battery, if that doesn't fix it, try the alternator.

[turdzi]

Thanx I will certainly start from doing just that.I let you know.

[bluetori]

It's carbon buildup exact same thing happened to my wife's on old q7, ran rough after sitting no check engine light even after replacing the timing chain and all components (with warranty thank god) it still had the same symptoms because it still had carbon buildup. I can almost guarantee that is what it is, does it only doing it in gear if an automatic? Power seem to surge when it's cold?

[chawaba]

It's carbon buildup exact same thing happened to my wife's on old q7, ran rough after sitting no check engine light even after replacing the timing chain and all components (with warranty thank god) it still had the same symptoms because it still had carbon buildup. I can almost guarantee that is what it is, does it only doing it in gear if an automatic? Power seem to surge when it's cold?

Car stumbles then backfires under load from a stand still mostly during the first half hour of driving the car. Had the car dynoed last month and dyno sheet showed some sort of surging at the higher rpm range. Had no problems on stage 2, only after the stage 2 B8.5 K04 install. Kinda confused now if it may be carbon build up.
[IMG][/IMG]

[turdzi]

Ok battery is charged and it didn't help.
Meanwhile I was wondering about suggestion that carbon buildup can be to blame.I have elementary knowledge about engines and how that work and I really struggle to buy it that reduced airflow in the head and intake can give misfire which deals like ignition or fuel cut.
Anyone can explain why ?

[van462]

Here is my best guess at it. On a cold motor at low RPM the cylinders fill with air only by the pressure difference created by the cylinder traveling down to draw in air. The throttle plate is mostly closed closed to create a higher vacuum. You are trading air volume for air speed in order to overcome the mass the air has to get it moving. The carbon built up on the valve stem can lead to a reduced opening size and less air flow. The air not only has a smaller pathway to flow thru its no longer smooth and creates turbulence. This will also decrease the speed of the air entering the cylinder. On a direct injection motor the fuel is sprayed into the cylinder. lower air speed results in poor air/fuel mixing. On a really cold motor the cylinder wall temp being lower may cause additional fuel puddling due to condensation. The ECU is in cold loop mode and using baseline maps. Usually a little rich to start with. Less air and the effect is an even richer mix. If you go too rich misfire or poor flame propagation occurs. One engine speed increases air velocity increases. You now have more air (mass) with velocity. Also turbo pressure is now available to fill the cylinders.

[turdzi]

Well it makes sense :)

[turdzi]

I kept troubleshooting and I've changed PCV since I had it at home. I'm runing out of options ant it looks like you guys might be right about carbon buildup :(

[Deacon_cs]

Hey, did you manage to solve the problem? I have the same issue..