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Tuner
one or two missfires on scanner
I scan almost every car that comes into the shop. I always have the cyl misfire pids open for the scan. My question is can you have a false misfires on the scanner with a stock motor (no aftermarket camshaft). For example If im scanning a motor that is healthy (good comp tests, acceptable cyl leak down tests) Sometimes I will see one ore two seemingly random misfires on the scanner. I cant feel any misfire's or hear any misfires but the scanner will display 1 or 2 for misfires pr/count on one or two cylinders out of the 8. The misfires seem to come and go with no rime or reason. This gets me to wondering are these real misfires or are they false.
ALL STOCK MOTOR QUESTION NONE OF THESE CARS IN QUESTION HAD ANYTHING AFTERMARKT. THEY WERE ALL STOCK
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Senior Tuner
Yes, misfire is an interpretation of some crank-jerk that
is outside expected timing, is all. The amount of jerk
goes up as the rotating mass gets lighter and the motor
gets more torque-impulse per stroke, which we all like
to go for. It's all arbitrary.
You could see stock motors jerk occasionally, I think
this is just the mixture dithering around and sometimes
going into the weeds. Doubtful it's a total fail-to-fire,
but just a punk charge and a weak firing could make
the "detect" threshold.
Short answer, fuggedaboutit until you see any kind
of consistency (single or group of cylinders that stand
out and keep hitting while the others are random or
zero counts).