Misfire count - but no codes!
08-06-2009, 08:55 AM
#1
Misfire count - but no codes! For a while now, ever since I got my scanner, I've been experiencing lots of misfire 'counts' on a single cylinder. While the others have some very spotty counts (usually no more than 2 or 4), this one cylinder is going nuts...especially when cold.
It the counts start at 2 and quickly go up to 12-14 and then drop down to 0. A few seconds/minutes later it starts up again from 2 to as high as 30. On a normal drive log, about 40-45% of the cells have a miss count of <0.
What exactly are these 'counts' and how many does it take for a misfire code to happen? I haven't gotten the dreaded of the P0304 (for cyl 4 misfire) even tho it seems to miss quite a bit. Is this harmful to the engine in the long run...I've replaced everything short of the fuel injector so if it's not that I'm guessing I should do a compression/leak down test.
It the counts start at 2 and quickly go up to 12-14 and then drop down to 0. A few seconds/minutes later it starts up again from 2 to as high as 30. On a normal drive log, about 40-45% of the cells have a miss count of <0.
What exactly are these 'counts' and how many does it take for a misfire code to happen? I haven't gotten the dreaded of the P0304 (for cyl 4 misfire) even tho it seems to miss quite a bit. Is this harmful to the engine in the long run...I've replaced everything short of the fuel injector so if it's not that I'm guessing I should do a compression/leak down test.
08-06-2009, 09:08 AM
#2
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Misfire counts have to be above a threshold for
some time to set a code. A low level of counts is
"normal". But a cylinder-cylinder discrepancy is
pointing to some sort of imbalance (like short
delivery on #4 injector, making a cold miss or
like that). Or plug gap, wire / coil insulation fault,
or ....
some time to set a code. A low level of counts is
"normal". But a cylinder-cylinder discrepancy is
pointing to some sort of imbalance (like short
delivery on #4 injector, making a cold miss or
like that). Or plug gap, wire / coil insulation fault,
or ....
08-06-2009, 09:15 AM
#3
Yeah I'm going to take a look at the injector this weekend when I have some time, I'm just wondering exactly how damaging these counts are...as I'm sure it's not normal for an engine to be missing.
I'm not worried about performance right now because 1) I won't be getting on it hard now and 2) in the few WOT/high load logs that I have done, there is absolutely no trace of misfires whatsoever...the counts only happen at light-moderate loads
I'm not worried about performance right now because 1) I won't be getting on it hard now and 2) in the few WOT/high load logs that I have done, there is absolutely no trace of misfires whatsoever...the counts only happen at light-moderate loads
08-06-2009, 04:08 PM
#4
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That's probably just a light lean miss, mine did it from
new (onesy-twosey-tensy kind of counts). Probably
the same place the motor shake comes from. I have
a theory that it comes from the PCM dithering the
mixture around (proportional fueling) to get cross-
counts up, which means it cycles between too-rich
and too-lean and only the average is ever right.
new (onesy-twosey-tensy kind of counts). Probably
the same place the motor shake comes from. I have
a theory that it comes from the PCM dithering the
mixture around (proportional fueling) to get cross-
counts up, which means it cycles between too-rich
and too-lean and only the average is ever right.
