2012 Audi Q5 Misfire

Zakk Technician Texas Posted   Latest  
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Driveability
2012 Audi Q5 Premium Plus 3.2L (CALB) 6-spd (0B6)
P0302 — Cylinder 2 Misfire Detected
P0303 — Cylinder 3 Misfire Detected
Misfire

This vehicle has a cylinder 2 misfire. It isn't a completely dead misfire but close to it. It came from the body shop and they tried to figure it out and swapped coils and plugs with no change. I performed an in cylinder running compression test with a pico scope and a wps500. Found the compression isn't the same every compression event with some being low and others being ok and others being in between. Also before performing this test I can hear a ratting in the valve cover right above cylinder 2. I ended up removing the valve cover because I thought I would see something obvious but of course everything looks ok. All other cylinders running compression looks ok. Does anyone see an issue with the waveform that I'm missing? 

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Milosav Engineer
Indiana
Milosav
 

I assume that you either have a broken spring or the rocker fell off the cam You might have to do a visual inspection under the cover

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Zakk Technician
Texas
Zakk
 

The valve cover was removed and visually nothing looks bad, unless it's like a hairline crack somewhere that I can't see. I even cranked the engine over with the valve cover removed and all rocker arms and valves are moving.

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Louie Technician
New York
Louie
 

Most likely you have carbon buildup behind the intake valves interfering with the valve action do a complete valve decarb very common with VW/Audi.

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Zakk Technician
Texas
Zakk
 

I thought of that but think it's strange that it's only one cylinder that's effected? I can try and rotate the engine with an inspection camera in the cylinder and try and see the tops of the valves.

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Dmitriy Analyst
Ontario
Dmitriy
 

Two engine cycles, on top of each other: diag​.​net/file/f62f0tslv… ​

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Joseph Technician
South Carolina
Joseph
 

Zakk, I pulled up your waveform, in my opinion the compression peaks are cyclical in sets of 3 (low, med, high) and the low ones show signs of volume loss. This would suggest to me that you have a valve that is not sealing very well most of the time. You could use another transducer in the intake if you have one or stick your wps in the intake and sync off of ignition to see if you are getting…

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Zakk Technician
Texas
Zakk
 

That's what I originally thought so I inspected the valves with a borescope and found no obvious issues. I then performed a cylinder leak down test and this cylinder has very little leakage. (only 10%). I tried to run a second channel with a delta sensor in the intake but the readings didn't seem right. I am not 100% sure my delta sensor is good. I was seeing pressure spikes in the intake the…

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Jose Educator
Texas
Jose
 

Could you share a cranking in cylinder waveform..also a snap throttle capture… to see if we can get more info… is looking like a valve sealing issue…

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Zakk Technician
Texas
Zakk
 

I can tomorrow, sorry. I leave my laptop at work.

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Richard Technician
New York
Richard
 

I agree with Milosav, that looks like a broken intake valve spring, Opening sometimes but not enough other times. Burnt valves tend to make the towers lean, while I think yours look good. But you can see the compression changing, which of course should be close to rock steady. I recall these valve springs being fairly recessed into the head. It might be tough to see. Can you air up the cylinder…

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Zakk Technician
Texas
Zakk
 

I would have to remove the camshaft to do that which involves alot of teardown. I'm trying to eliminate any other issue before anymore teardown.

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Charles Technician
California
Charles
 

Broken intake valve springs are pretty common on that engine, some have been pretty hard to see until it was removed.

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Zakk Technician
Texas
Zakk
 

Thanks for the info. I'll recheck tomorrow to see if I find anything.

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Chad Diagnostician
Arizona
Chad
   

Good Evening Zakk, Your cranking capture with the pulse sensor shows that you are leaking pressure past the intake valve as the piston is ascending upward on its compression stroke and exhaust stroke. Your running capture does not show any real sign of a valve seating issue as the pockets are fairly symmetrical with no cuts lasting more than a millisecond. However, intake valve seating issues…

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Zakk Technician
Texas
Zakk Update
 

ok everyone I have a capture of a snap throttle for cylinder 2 and a snap throttle for cylinder 4 (good cylinder). I removed the valve cover again and very closely inspected the valve springs and still not finding anything wrong. I then inserted a borescope into the cylinder and opened the intake valves and found heavy carbon build up on top of the valve (see pic). I am going to sell a carbon…

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Zakk Technician
Texas
Zakk Update
 

Well the intake cleaning didn't fix the issue. Still have a misfire on cylinder 2 at idle and can hear rattling in the valvetrain right above cylinder 2. I'm suspecting a broken valve spring but like I mentioned before I inspected them very closely and didn't see anything wrong. Also when driving the vehicle it seems to perform just fine at higher RPMs. I feel like if there was a cracked valve…

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Louie Technician
New York
Louie
 

Hi Zak I experienced similar I intermittent random misfires when I worked for audi​.​They would send an engineer to the dealership he narrowed the misfire to low compression due to faulty intake valve sealing,we would attempt hand lapping new Valves but that made it worse the only solution was a new cylinder head he said Audi uses a special process involving a laser to match The…

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Gil Technician
California
Gil
 

I’ve seen broken springs before in cylinder with pico scope and they don’t look like that, weak springs will always be weak , but they can float at higher rpm , so if you slow it down to only cranking compression at wide open throttle at 2 sec per division at least 10 seconds, if peaks are not even then may have a rocker arm issue (rollers?) my 2cents but worth a try, compared to good cylinder…

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Zakk Technician
Texas
Zakk Update
   

OK, so I started fresh this morning and recaptured cylinder 2 cranking and cylinder 1 cranking and I noticed that cylinder ones compression peaks aren't the same and it's kinda acting like cylinder 2 but not as bad. I didn't notices this before. I also found cylinder 2 IVO jumps around throughout the different rotations. I found one event at 6 degrees ATDC and another event at 4 degrees BTDC. I…

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Dmitriy Analyst
Ontario
Dmitriy
   

Zakk, one can not trust phase rulers if a cylinder leaks bad enough. This one looks like a leak: diag​.​net/file/f7cxjezk2… ​ but it would be much easier to see if the throttle was open – your waveforms look like the throttle body is plugged shut, why is that?

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Zakk Technician
Texas
Zakk
 

I capture these waveforms with the throttle closed due to if it was open there wouldn't be any vacuum pockets which makes diagnosing slightly harder in my opinion. Here is a waveform of cylinder 2 cranking with the throttle open.

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Zakk Technician
Texas
Zakk
 

Also I agree that some look like they are leaking. I performed a cylinder leak down test with cylinder 2 at top dead center compression and found no leaks. So my question is the ones that look to be leaking can it be due to a timing issue? When I measure for IVO on the events with low compression I get a different reading then the ones that have a closer to normal compression reading.

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Dmitriy Analyst
Ontario
Dmitriy
 

I put 1440 deg phase rulers on two “good” compression peaks, and they show consistent IVOs, even though there is a “bad” peak in between: diag​.​net/file/f63cmogrs… ​ So I think the “wandering IVO” is more of a product of a “wandering compression peak”, which happens when there is an actual leak and the compression tower is leaning. I know you tried to use the pulse sensor to…

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Zakk Technician
Texas
Zakk
 

Awesome. Thanks for the info. Unfortunately I don't work tomorrow and won't be back to the shop until Tuesday. I'll try that then and keep you updated. Thanks again.

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Chad Diagnostician
Arizona
Chad
   

Good Afternoon Zakk, After laying cylinder 1 over cylinder 2, it is clear there is not a carbon build-up issue and the valve events are occurring at the same time which means there is not a phasing or timing issue. Your first cranking capture clearly showed that you are leaking compression when the piston is ascending on its compression stroke. You need to stay on that path! There are only two…

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Travis Diagnostician
Texas
Travis
 

Following

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Brian Owner/Technician
Prince Edward Island
Brian
 

Just starting to get into this type of diagnosis and am following closely . My 2 cents worth is possibly it has to do with valve rotation and the valve face and/or seat are not true which may not be allowing the intake valve to close fully at certain points of it's rotation . It looks like the pattern repeats itself.

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Jose Educator
Texas
Jose
 

I agree…

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Zakk Technician
Texas
Zakk Update
 

Sorry to disappoint everyone but I showed up to work today and the Audi was gone. I guess once they herd it was an internal engine issue they didn't want to proceed with the diagnostic. I didn't get to talk to the customer because they came in on my day off. Thanks for all of the help and information!

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