Cold start misfires!

TYb

Registered User
Best case I can see an adjudicator recommending a 50/50 split. From what you’ve said above there was no way of your dealer knowing of the damage when they prep’d the car for sale.

You could argue it’s a manufacturing defect but that’s pretty much impossible to prove.

If there is chance I would reject the car, remove the parts you have added and start again.
 

Damo S

Registered User
They might have known had they gone rummaging about through the misfire logs. However, the whole point of a warranty is that it covers failures that occur during that period (pre-existing or not). Given that symptoms began more or less as soon as I bought the car I don't see how that makes me half liable (50/50 split).

But, I do see how this will be a very grey area given the nature of the problem (foreign object invasion rather than component failure).
You might be right and that may well be all I get, but I will push for more as I think its very clear that the problem already existed and was not caused by me so I feel I have no liability at all.
 

TYb

Registered User
They might have known had they gone rummaging about through the misfire logs. However, the whole point of a warranty is that it covers failures that occur during that period (pre-existing or not). Given that symptoms began more or less as soon as I bought the car I don't see how that makes me half liable (50/50 split).

But, I do see how this will be a very grey area given the nature of the problem (foreign object invasion rather than component failure).
You might be right and that may well be all I get, but I will push for more as I think its very clear that the problem already existed and was not caused by me so I feel I have no liability at all.

I’m not saying you are liable at all, It’s just not clear the dealer is as well, for your sake I hope it’s receitifed fully at no cost to you, I just know how tricky this could be.
 

CoffeeAndJam

Registered User
Turns out I’m not having very good luck with my car. It’s back in the shop for another major repair after buying a new engine...

I have to shell out $2800 for a new turbo (installed) because the wastegate actuator is intermittently malfunctioning, putting my car into limp mode and giving me a P00AF code.

Of course Audi doesn’t sell the part separately, and the aftermarket part installed would cost me $1500, so I might as well spend a bit more for a whole new turbo.
 

AlS3BE

Registered User
Turns out I’m not having very good luck with my car. It’s back in the shop for another major repair after buying a new engine...

I have to shell out $2800 for a new turbo (installed) because the wastegate actuator is intermittently malfunctioning, putting my car into limp mode and giving me a P00AF code.

Of course Audi doesn’t sell the part separately, and the aftermarket part installed would cost me $1500, so I might as well spend a bit more for a whole new turbo.

That’s very unlucky mate.
Cars unfortunately are just money pits. Hope you get it all sorted soon.
 

CoffeeAndJam

Registered User
Oh man thats terrible. sorry to hear that :(

Yeah, not easy to justify after spending almost $8k on an engine.

Bit of an update to anyone following this thread: New turbo was installed. I picked up the car today. No more wastegate actuator code being thrown now, so that’s solved.

So far did two cold start tests where the car sat for over 2-3 hours in 30F weather, and cylinder 4 is misfiring more now after the new turbo.

First cold start had 35 misfires in cylinder 4. Second had 21 in cylinder 4. Most yet since I’ve gotten this engine. No CEL’s or codes have been thrown for misfires just yet which is good (except when my wastegate actuator failed and threw my car into limp mode).

I’m just about to give up trying to figure out what’s causing the misfires in cylinder 4 on cold starts. Maybe it’s normal to have a few that don’t cause a CEL.

To recap what’s been done:

- Replaced all coil packs
- Audi applied “software update” to fix cold start misfires (didn’t fix it)
- Replaced all injectors
- Bought like-new used engine (10k miles on it) once borescope revealed damage in cylinders that were misfiring
- replaced all spark plugs (part of 40k mile Audi Care service)
- installed new turbo due to faulty wastegate actuator

Still no fix for the cylinder 4 cold start misfires. Don’t know what to do next without blindly throwing more money and parts at it.

Could it be the intake manifold since it’s one of the only things that hasn’t been replaced yet?
 

Damo S

Registered User
Id like to say that it sounds electronic but I know from my own problems that the ECU is very good at fudging the engine "run" with only a low percentage of revolutions recording misfires even then there is physical damage to the camshaft.

what I dont know is whether there are specific sensors to detect cylinder specific misfires. There must be something for it to be able to register although I dont believe there are knock sensors per cylinder. Misfires as I understand at are not just instances of pre-ingition, it is "when the ecu detects an unusual cycle for a complete revolution of a particular cylinder" to roughly quote the master technician when chatting about my car. I wish I understood more about exactly what that means, and how such events are detected / calculated. This knowledge may shed some light on a way forward for you.
 

ZipZap01

Registered User
Misfires are detected with the crank position sensor. This sensor generates a pulse every few degrees of rotation.

When a cylinder fires, the engine should suddenly accelerate its rotation as it is accelerated by the combustion. The rotation will then slow down over the next 180 degrees as the next cylinder compresses.

The ECU looks for the sudden acceleration of rotation over 30-60 degrees after a cylinder fires. The rate of acceleration is compared to a reference based on what the expected engine load is. If a cylinder shows anomalous low acceleration it is recorded as a misfire.
 

CoffeeAndJam

Registered User
Misfires are detected with the crank position sensor. This sensor generates a pulse every few degrees of rotation.

When a cylinder fires, the engine should suddenly accelerate its rotation as it is accelerated by the combustion. The rotation will then slow down over the next 180 degrees as the next cylinder compresses.

The ECU looks for the sudden acceleration of rotation over 30-60 degrees after a cylinder fires. The rate of acceleration is compared to a reference based on what the expected engine load is. If a cylinder shows anomalous low acceleration it is recorded as a misfire.

Interesting and good to know. Not sure how I can use that info to help diagnose the issue I’m having, though. Everyone seems to be stumped, both at Audi and the specialist techs. They both seem to think everything is fine as long as no codes appear.

My fear is something slowly happening over time. I have nothing to back that up, however. Just quirky misfiring in cylinder 4.
 

CoffeeAndJam

Registered User
Update:

New turbo didn’t fix the P00AF wastegate actuator error. Car went into limp mode on my way home from work and when I scanned it, there’s a pending P00AF code.

I’m stumped as to what would cause it. Faulty ECM? It’s a brand new turbo...
 

ZipZap01

Registered User
P00AF means that the ECU is seeing the wrong boost level compared to what it has requested/is expecting.

Usually means a boost leak/vacuum leak (e.g. cracked manifold, intercooler, loose intake pipe, etc.), but could also be a faulty wastegate actuator, faulty wiring/connection to the wastegate actuator, incorrect mapping of the ECU (particularly if turbo has been changed from stock)
 
I'm having a similar issue and changed almost everything except the cylinder head.

Weird thing, I get the misfires mainly on #4 only after 6000+k rpm. The car detects misfire, then hides that cylinder and the car sounds like a Subaru. Turn off/on cat goes back to like nothings wrong etc.

I tried turning down boost, changed injectors (DI & PI), sparkplugs, gaps, coilpacks, intake manifolds, etc. All the same.

Considering this to be same situation, could maybe suspect it's in the head and I should swap. The current head is slightly ported and polished on the intake side too with upgraded springs and retainers and OEM valves.

Been chasing this issue for awhile without much luck. Others I have talked to, are having same issues too.

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AlS3BE

Registered User
I'm having a similar issue and changed almost everything except the cylinder head.

Weird thing, I get the misfires mainly on #4 only after 6000+k rpm. The car detects misfire, then hides that cylinder and the car sounds like a Subaru. Turn off/on cat goes back to like nothings wrong etc.

I tried turning down boost, changed injectors (DI & PI), sparkplugs, gaps, coilpacks, intake manifolds, etc. All the same.

Considering this to be same situation, could maybe suspect it's in the head and I should swap. The current head is slightly ported and polished on the intake side too with upgraded springs and retainers and OEM valves.

Been chasing this issue for awhile without much luck. Others I have talked to, are having same issues too.

Sent from my Pixel 3 XL using Tapatalk

Is there any reason for the uprated valve springs ?
Are you running aggressive cams?
Not sure on turbo cars but when I used to mess around with NA cars uprated springs were only necessary on high revving aggressive cams otherwise it can cause things like misfires and many other things.
Another thing to look at as yours is tuned is the fuelling. On a dyno it can be ok as you are progressively mapping the ecu and gradually adjusting the fuelling. When you kick down the car suddenly needs extra fuel and possibly the fuel pump isn’t managing to maintain pressure or getting up to pressure quick enough.
Last thing I can think of is the knock sensor detecting knock and pulling timing/fuelling etc.
 

matthew999

Registered User
I completely understand. I don’t see it as being negative! I don’t want another melted engine, either. The shop that’s helping me is one of the best in the state, and I guess I’m trusting them with their recommendations and course of action. They want me to monitor it as they don’t think there’s any problem with the car right now and think the misfires are within operating spec, or it would be throwing a code or trigging a CEL (which it hasn’t since the engine was installed last month).

I don’t have VCDS. Wish I did. I’m using OBD Fusion on my iPhone, connected to a Kiwi Bluetooth/WiFi OBDII reader. Not sure what you mean by turning management light... sorry. No light comes on anywhere, if that helps!
Sorry to resurrect an old thread. I wanted to ask if you had to enable any custom pids to use obd fusion to get live sessions for missfire count per cylinder. Any tips would be great. Thanks

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Is there any reason for the uprated valve springs ?
Are you running aggressive cams?
Not sure on turbo cars but when I used to mess around with NA cars uprated springs were only necessary on high revving aggressive cams otherwise it can cause things like misfires and many other things.
Another thing to look at as yours is tuned is the fuelling. On a dyno it can be ok as you are progressively mapping the ecu and gradually adjusting the fuelling. When you kick down the car suddenly needs extra fuel and possibly the fuel pump isn’t managing to maintain pressure or getting up to pressure quick enough.
Last thing I can think of is the knock sensor detecting knock and pulling timing/fuelling etc.
So figured out the issue. There is the side egr valve on the side of the head on the back under the hpfp. That was not sealing correctly and leaking air causing the misfires on higher rpm ranges. I would either replace (about 150ish bucks) if you remove it and can blow on the plastic piece and air comes out.

Other option is blocking it off with a PR plate and then coding the SAI pump out.

Part# in description
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