Audi misfire from low compression

Sadel Owner/Technician Ohio Posted   Latest  
Demonstration
Driveability
2014 Audi A6 Premium 2.0L (CAED) (0AW)
P0301 — Cylinder 1 Misfire Detected
Runs Rough
Check Engine Ligh On

This Audi came to me from another shop, they asked me to look at it for misfire and rough running. They had already done plugs and coils, and they said they had seen “smoke” coming out of the intake manifold from one of the hose ports when opened , at some point during their testing. That portion had me puzzled , and my mind kinda jumped to an intake valve issue. But after testing and poking around, I found the loss of compression to be going into the crankcase, and for there to be definite mechanical issue with it. And I realized the “smoke” was most likely what was compressed and sent into the crankcase and being seen come out of the breather hose port , since its big easy hose on intake to get off. Along with finding the root cause, I also got lucky to have taken a step back and slowing down and taken a careful look at the engine again and avoiding a second mistake of another bad piston. Needless to say, after all was replaced and repaired it all worked out ok. If watch it, I hope it helps in some way or another, and thanks in advance.

youtube​.​com/watch?v=C60mQ2…

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Timothy Owner/Technician
Wisconsin
Timothy
 

I'd have just sold him the engine! Any thoughts as to why the pistons failed? I'm not aware of this being a pattern failure on this engine. I've looked at a bunch of burned pistons, and they always start to fail from combustion heat from the top down, not from the bottom up. The heat weakens the piston at it's weakest point, and causes the whole side of the piston to soften from the compression…

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Paul Mechanic
Illinois
Paul
 

I give you a ton of credit for your dedication and perseverance, very impressive. I think I would only go that far if it was my own. If I couldn't identify the cause of failure, I wouldn't be comfortable repairing it and having to stand behind it. I, too, would sell customer a unit that has some sort of warranty, wether new, used. I did do one though this summer that chain snapped- 2013 Malibu…

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Sadel Owner/Technician
Ohio
Sadel
 

Thank you Paul, and yes I actually don't mind “opening up ” engines at times, engines along with electrical diag stuff is my passions, but yes I also do it when it makes sense to do so as well (business wise) when doing it for a customer. I figured this one would be cool to share since it has both some diag approach and actual physical tear down of root cause. And not sure if you read my other…

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Paul Mechanic
Illinois
Paul
 

Yes, I read your reply. Your hypothesis (and I'm not disagreeing by any means) begs the question why aren't there other two, 2 and 4 showing signs of you can see? Are/did you plan on replacing all 4 sat this point?

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Sadel Owner/Technician
Ohio
Sadel
 

This was last summer when I filmed it, so yes all got replaced , and 2/4 still hadn't come apart but I'm sure they weren't far behind

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Sadel Owner/Technician
Ohio
Sadel
 

Hey Tim, At first , I was “comfortable” just doing “one piston" …. and kinda chalk it up as all of a sudden one randomly failed , “just replace it ” and should be good. The reason why I was “ok” with doing that is because I do do a lot of engine work as well, and have learned with experience and knowledge as well, that I have been able to replace a piston at a time from any make engine and…

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Timothy Owner/Technician
Wisconsin
Timothy
 

Yeah, way back when I raced, I raced exclusively Ford turbo engines, back when Ford had an exceptionally ugly car called the Merkur xr4ti. Raced in the 24 hour series back then, sponsored by PlayBoy magazine. Had tons of fun, lost tons of money, never won a damn thing! But learned how to destroy all kinds of car parts, from transmissions, rear ends, camshafts, etc. But, I used some very stout…

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Sadel Owner/Technician
Ohio
Sadel
 

Wow Tim, I bet that was awesome times racing, and to do it back then I bet was a challenge based on how far the industry has come. And I never did measure the boost pressure on the vw/ audi's but from other manufacturers that I have actually measured they are running 12-15psi on the bmw's and I did measure on a L15 Honda engine once and I was surprised to see that in factory form running around…

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Timothy Owner/Technician
Wisconsin
Timothy
 

I spent most of the races, ‘racing’ in my rearview mirror! I was up against some truly big-buck teams, with unlimited budgets. They'd lap us slower cars about every ten laps or so. It was still a good time.

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Marty Technician
California
Marty
 

Thanks for the info, Just wondering what the cylinder walls looked like? It seems odd that with the extent of damage to the piston's and all the chunks in the the pan it did not result in scoring..? Looks like the # 1 piston you showed did have scoring on the skirt area…was anything done to the cylinder prior to installation? I realize there is a hardened coating on the cylinder wall so…

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Timothy Owner/Technician
Wisconsin
Timothy
 

From the camera shot of the cylinder walls, I saw no evidence of any scoring whatsoever. The hardened liners are much tougher than the pistons, and the rings. I am also very doubtful that he'd just plop a couple of pistons into damaged cylinders…

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Sadel Owner/Technician
Ohio
Sadel
 

Thanks Marty , There wasn't any damage that I was concerned with, despite the situation, I was surprised myself

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Craig Diagnostician
Illinois
Craig
   

Sadel, this problem you're describing is indeed caused by the use of incorrect oils. It's becoming a huge issue in GDI motors, the phenomenon is called “low speed pre ignition” if you Google it there is more information out there. motor​.​com/magazine-summa…

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Sadel Owner/Technician
Ohio
Sadel
 

Craig, thanks for the link, good article. And yeah I remember info on it also from a worldpac class last year that was offered during lock down, and it was just after having to deal with this vehicle so I kinda ended up putting the two together and had advised the shop to use the correct oil . Thanks for the info once again.

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Cmore Mechanic
Connecticut
Cmore
 

So these guys changed the plugs and coils on an engine with no compression in one cylinder??!! I wonder if this is the same shop that changed the engine cause the alternator was locked up?

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Jamie Owner/Technician
South Carolina
Jamie
 

I just replaced engine in 15 A4 with the caed with #2 piston bad. It had a broke valvespring about a month previously on same cylinder. The caed must not be any better than caeb engines

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Daniel Owner/Technician
Virginia
Daniel
 

We had one of these in my shop several months ago. Piston broken just like this. In my opinion, I think it is a problem with pre detonation. Maybe using low octane or cheap gas. The vehicle we pulled down had an aftermarket tune and intake installed. Good write up though. Some of these Euro engines are so expensive, even used, repair is sometimes more cost effective.

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