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Old 07-19-2014, 02:31 PM   #1
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Default need help with misfire on my 2.7t c5

hi, i have a 2000 audi a6 with the 2.7t. yesterday, it had a steady misfire when i got in it to drive it, but it went away after a few miles of driving. this morning i got in it to go, and same misfire. this time it wont go away and is a very steady misfire. also, after driving it about ten miles, i got home, shut off the car, and noticed a light trail of smoke coming from the drivers side wheel well. i noted that it was from the drivers side only. the power steering has been a little bit stiffer than normal in the past 2 days, but i dont see that being related to the misfire. i put the scanner on it and this is what i came up with.

16518 o2 sensor bank 1 sensor 1 no activity

17861 exhaust gas temperature sensor1 (g235) open short to plus p1453

16684 random/multiple cylinder misfire detected p0300

16689 cylinder 5 misfire detected p0305

17523 o2 sensor heating bank 1 sensor 1 short to ground p1115

16686 cylinder 2 misfire detected p0302

when i look at diagnostics i see that cylinder 5 is misfiring steadily/constantly, and the others for the most part do not misfire. i have tried moving plugs/coilpacks from cylinder 5 to 6, and misfire stays at cylinder 5.
help please!
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Old 07-19-2014, 02:47 PM   #2
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Pre-cat O2 sensors can and will cause your engine to misfire. I searched high and low for what was causing mine at the time and finally narrowed it down to the pre-cat driver side O2 after many people posted that an O2 would not cause those symptoms. Are you getting a flashing check engine light while driving? If so, don't. I'd probably start there since you are dealing with a random misfire on top of cylinder 5, but others with more experience may have greater insight based on the EGT code you're getting.
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Old 07-19-2014, 02:53 PM   #3
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Quote:
Originally Posted by jandsbulldogs View Post
hi, i have a 2000 audi a6 with the 2.7t. yesterday, it had a steady misfire when i got in it to drive it, but it went away after a few miles of driving. this morning i got in it to go, and same misfire. this time it wont go away and is a very steady misfire. also, after driving it about ten miles, i got home, shut off the car, and noticed a light trail of smoke coming from the drivers side wheel well. i noted that it was from the drivers side only. the power steering has been a little bit stiffer than normal in the past 2 days, but i dont see that being related to the misfire. i put the scanner on it and this is what i came up with.

16518 o2 sensor bank 1 sensor 1 no activity

17861 exhaust gas temperature sensor1 (g235) open short to plus p1453

16684 random/multiple cylinder misfire detected p0300

16689 cylinder 5 misfire detected p0305

17523 o2 sensor heating bank 1 sensor 1 short to ground p1115

16686 cylinder 2 misfire detected p0302

when i look at diagnostics i see that cylinder 5 is misfiring steadily/constantly, and the others for the most part do not misfire. i have tried moving plugs/coilpacks from cylinder 5 to 6, and misfire stays at cylinder 5.
help please!
Pull the spark plug on #5 and tell us what it looks like. How long since you changed plugs? Look of vacuum leaks.
My S6 had a misfire…the technician apparently didn't tighten the plug enough and it came loose…right around 30K miles ago the car had a low-mileage used engine put in it and new TB service, rest of rubber stuff, new plugs, etc. But the loose plug caused the misfire..I was just lucky the combustion didn't eat a hole in the aluminum head along the plug threads!

Last edited by SloopJohnB@mac.com; 07-19-2014 at 04:55 PM.
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Old 07-22-2014, 09:11 AM   #4
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it IS a flashing CEL light.
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Old 07-22-2014, 01:48 PM   #5
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ok so i pulled the plugs on cylinder 5 and 6. there was a little amount of oil on mainly the 5th cylinder one. cleaned up and didnt help...
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Old 07-22-2014, 03:25 PM   #6
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Swap coils? If not, look at the o2 sensor. Either pre-cat o2 that is faulty can readily cause similar symptoms. There are plenty diys on here about how to swap them out.
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Old 07-22-2014, 05:00 PM   #7
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And…how long have the plugs been in there?
Over 30K miles, change them.
There should be NO oil on the plugs…ok on the threads when you pull them out but not on the hot end. These things run dry as a bone.
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Old 07-23-2014, 06:08 PM   #8
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i have switched coilpacks between the 5th and 6th cylinder with no change...still a steady cylinder 5 misfire. when i shined a light in and looked at the cylinders the 6th is dry, where inside the 5th is wet looking...i took brake cleaner and cleaned off both the plugs, and blew them dry with air, still the steady knock on #5. the plugs im sure could be changed but i dont think they are my main problem as of now because of switching plugs between cylinders as well, with the misfire staying at the 5th cylinder. so should i go after 02 sensors now?
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Old 07-23-2014, 06:14 PM   #9
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i also put the air nozzle down in cylinder 5 and shot some air in there to dry it out, a white cloud of (smoke) (dust)? came out, with a burnt smell. dont know if that is relavant.
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Old 07-23-2014, 07:10 PM   #10
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It's not.
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Old 07-23-2014, 07:10 PM
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