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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.

Engine code:

  • 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).

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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.)

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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.

  • Probably the driver inside ecu. – narkeleptk Dec 13 '19 at 18:48
  • Thanks @narkeleptk. Would I have to replace the entire ECM? (Looks like that runs $600 or so.) Or is the driver for the ECU something different? – Cullub Dec 13 '19 at 18:53
  • Rule out everything else before swapping out the ECM since, as you discovered, that is a very expensive part. For a 2005 model, you may be better off looking at a salvage ECM vs. a new one. But I'm going to guess that it's something other than the ECM until you have ruled out plugs, coils, wiring, valves, cylinder, piston, and fuel injectors. – jwh20 Dec 13 '19 at 18:55
  • @jwh20 we've pretty definitively ruled out spark plugs (replaced multiple times actually), replaced the coil (and tried switching around). Compression test went fine (and it was pretty sudden which would be surprising for compression). I am 95% certain it's not getting spark though. How might we test the wiring? – Cullub Dec 13 '19 at 19:08
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    @Cullub nah don't have to replace. You can send it out for repair. prob around $100-$200. Keep in mind I'm not saying for sure its the ecu but its a common fault when all else is good. Its pretty easy to test just need to find the schematics for your year/model. I don't do a lot with audi so I'm not too sure which system they use. Are the coil packs 2, 3 or 4 wire? – narkeleptk Dec 13 '19 at 20:44
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From the information you provided it could be a couple things including the ECM as mentioned. But Im assuming youre using an after market scanner? and you may not be receiving all the fault codes. If you do replace the ECM it would need to be coded to the vehicle. I would suggest, as a first step, to get a dealer to scan the vehicle for faults. Or even better, purchase or find someone local with a ross tech vag-comm and see what other codes you may have. In my experience this sounds like it could be the timing or intake, but there would be other faults.

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  • Yep, I'm using an aftermarket bluetooth OBDII scanner from Amazon. – Cullub Dec 14 '19 at 4:48
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Be sure of proper plug wires to coil pack. If you think a plug is not firing pull the wire from the coil pack and use jumper from cpk to very close to chassis ground. If coil no spark then look at module to coil pk.30$@ salvage. If think test is good put wire back to module then pull wire from plug insert screw driver in wire hold close to chassis and spin eng each time if no spark, bad plug wire. You can borrow another wire to perform this bad wire test. Temporary...The module to coil pack are subject to failure. DO Not Test module while plugged to ecm. If suspect module again go to salvage.repeat trip for exchange.

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