I have a 2005 Audi A6 Quattro with a 3.2l V6. My brother just purchased it from our local Craigslist, and we didn't check it over very thoroughly before purchasing, but at time of purchase it ran perfectly. The one problem at purchase time was that the MMI (the infotainment system) didn't work at all. Not sure if that's related.
Fast forward two days (during which time we'd been driving it). He was driving back from a friend's house and as he accelerated around a left turn he felt it lose power slightly. On the road it was running rough and having trouble accelerating. Within a mile, the CEL came on (flashing), a message came on the dash display "ESP Fault", and it the engine was running really rough. He nursed it home.
- P0303: Misfire on cylinder 3
We have driven it a bit since then (a few miles here and there), but the problem has persisted. We then tried replacing the spark plugs, which didn't fix the problem. Next, we tried replacing the coil pack on cylinder 3, which he thinks helps slightly (although I'm conflicted).
During this process, the car had begun starting hard (it would take a couple turns to start the engine rather than starting right away). This gradually got worse through the process until it needed a jump to start despite having a fairly well charged battery (I confirmed 12.5v on the battery, and we bought a second one just in case). Just today, I took the spark plugs out to remove compression, which allowed the engine to turn over a few times. My guess is that we burned out the starter. This morning that stopped working as well, and the starter caught on fire for two seconds or so (!), so I'm going to replace that for sure before turning the engine over again. (For the record, we just changed the oil and the level is fine.)
Next test was to bring it into the heated garage (we're in MN and it's 16 degrees outside), and test for spark. We have an inline spark tester, and confirmed (first of all) that cylinder 2 is sparking (to test our setup). We then tried to turn the engine over with the same coil and spark plug but with the setup plugged into cylinder 3's plug and we couldn't confirm that it sparked! This was right around the time that the starter completely failed, so the test wasn't super rigorous, but I'm fairly certain that cylinder 3 is not getting ignition, and the problem is upstream of the coil pack.
My question is: what can I test/replace/fix? The same set of wires appear to also travel to cylinder 2, which works fine, and comes from behind the firewall.