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Discussion Starter · #1 · (Edited)
I'm very green (read: I just pulled out my eBay cable for the first time today) with VCDS, and I'm trying to verify that my new ignition coil fixed my misfire problem. (Short summary: I was out of town when the engine shook like an unbalanced washing machine. I stopped and restarted and my blinking CEL went to a solid one. Code scan said cyl. 2 misfire. I replaced the coil, reset the codes, and drove home.)

I figured out how to read codes and how to display misfire counts. (Yay Internet!) My question is: Do the misfire counts reset whenenver I turn off the car, or do they only reset when resetting codes?

(I'm hoping the answer is "only when resetting codes" as my wife was planning on taking the car out of town this weekend, and I don't want to discover that it was some problem other than the coil when I'm not around to fix it!) FWIW, no misfires were posted while I ran the engine with the car in the garage.

EDIT: Took it out for a little drive, and did see the misfire count cycle between 1 and 0 on a couple cylinders, so it apparently resets itself on a periodic basis. Do I still have a problem, or is this within limits?

Another EDIT: Looking around online, it appears that everyone talks about it resetting with every start, yet I clearly see mine go back to zero several times just while driving around the neighborhood. What gives?
 

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I found this out when I was trying to track down my misfire codes. The misfires reset every minute or so while the engine is running.. I ended up running a log while I was driving the car to better track it. I think there was a way to count misfires between starts, but I don't remember exactly.
I never found a way to keep a misfire count from resetting each start.
 

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Discussion Starter · #3 ·
I wonder how many misfires is too many? I know ideally it's zero. I know if I watched that counter scroll up to hundreds, I'd be in trouble, but if it never goes past one or two?
 

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I never went much higher than 20 as I recall. Once I got everything fixed I went to zero. My thoughts would be that you can live with one or two occasionally but it is probably just a sign of what's coming soon. What cylinders are getting the misfires or is it all. Have you checked the ground is tight and clean?
 

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It resets with every ignition turn, and then automatically as whirlybird stated at some timed interval as you actively monitor it. Logging is the the way to really monitor it over time.

I don't think 1 misfire is severe, but you shouldn't be getting any. Problem with misfire monitoring is that it's all guesswork by the knock sensors, some are anomalies and some are true misfires. Blinking CEL is triggered by a certain number of misfires within a given amount of time, hence why it resets so often. Easier to program a timed reset so that you don't have to save time stamps maybe? Not sure...
 

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sirwired, the behavior you describe is probably happening in any car out there. No need to worry about a few misfires showing up.
 

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Problem with misfire monitoring is that it's all guesswork by the knock sensors, some are anomalies and some are true misfires. .
They actually measure the acceleration of the crankshaft (through the crank position sensor) on each firing. Is not always very obvious, so that's why the ecu resets the count and won't signal some random misfire. A constant pattern of misfires will trigger a CEL but what the OP describes is negligible.
 
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