First time poster, but a veteran at digging through this forum for info.

A few months ago while I was deployed my wife informed me that our A6 was running rather rough and that she thought it was a head gasket going. Well, after I returned I was relieved to find out that it just had a misfire (p0300).

STEP 1: I replaced plugs and coil packs since the car needed new plugs anyways. This did not really make a difference.

STEP 2: I performed a compression test and discovered that all cylinders were right around 160 psi, except for #5, which was at 140.

STEP 3: Poured a little oil onto the cylinder head and was able to achieve a compression of 170 psi

I put everything back together, and it ran a little bit better, but still has a noticeable misfire. I'm afraid it might be a piston ring. I'm pretty sure I'm just in denial...but I'm really hoping that there could be another reason.

So, to sum it up:

-New plugs
-New coil packs
-Poor compression on #5
-Compression improved with "oil trick"
-Engine still runs poor

Any suggestions you guys have would be appreciated

 

Is the misfire always present while running? P0300 is a random misfire. If the code was P0305 I might be more inclined to believe it was something with that particular cylinder. It could be the fuel system. I'd recommend running some Sea Foam in the fuel and let it clean the injectors. I'd also recommend a new fuel filter. When changing it, be sure to capture all the fuel that leaks out and inspect for water or other contaminates.

 

I'm sorry, I forgot to mention that I was able to catch a P0305 code, but only while driving it. I took my code reader with me for a ride and was able to catch that code only when the check engine light started flashing.

 

The fuel system could be the culprit of a misfire, however it wouldn't explain why there is poor compression on that cylinder.

 

I'd still run a can or two of Sea Foam through it. In the oil and the fuel system. Plus you might pour a bit of Sea Foam down in the cylinder and let it sit over night to see if it might loosen up a possible "stuck" ring. Be sure to turn the engine over (by hand preferably) with the spark plug out of that cylinder before attempting to start it again to prevent a potentially damaging hydraulic lock.

If that doesn't work, it sounds like it's exploratory surgery time...