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10 CRV 2.4 interesting false misfire count

  • Doodah14
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8 years 2 months ago #14477 by Doodah14
2010 Honda CRV, a customer brought it in for a shudder right after the 4th gear shift on a cruise type acelleration. On my test drive, i had my scanner on the misfire data on graph. (So I could drive the car without having to stare at the pids as the graph will auto range.) When the shudder occurred I paused the graph. On review of the graph, cyl 2 had a range of 164. When I reviewed the graph the missfire counter spiked from 0 to 164 then back to 0. The graph looked like this. ___]____. I drove it several times doing the same thing and came up with the same results. The misfire all on cylinder 2 ranged from 164 to 2100 all looked like a millisecond spike on the graph. I did some research and some tests and I found out that there is a relearn for the crank pattern that can be done to resolve false misfire count on this model. I did that, no change. Eventually I proved that there was a Tcc issue that was causing the shudder. (I will try to attach a photo of the scanner data)
I don't do trans work so I recommend a local trans shop to repair the shudder issue.
I likely won't be able to do anymore testing on this Vechicle. But I'm really curious about this misfire data and would like to hear any thoughts or opinions on why this would happen.
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8 years 2 months ago #14478 by Doodah14
Replied by Doodah14 on topic 10 CRV 2.4 interesting false misfire count
Also on this model there 3 pids for each cyl misfire counter, for example, cyl 1 misfire a, cyl 1 misfire 1b, and total misfire 2. The spike was in a or b randomly but never showed In total. And never set a misfire code.

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8 years 2 months ago #14499 by EricGoodrich
Replied by EricGoodrich on topic 10 CRV 2.4 interesting false misfire count
Misfires on the CR-V are detected by measuring the speed of the crankshaft. When a cylinder misfires, the Piston does not push the crankshaft and the crankshaft slows down. The crank sensor is efficient enough to tell the computer that this happened and a misfire is counted.

The problem we run into sometimes it's that there are plenty of things that can cause a crankshaft to slow down.

As far as torque converter clutch diagnosis goes, one thing I look at is the speed of the crankshaft during the "judder". The crankshaft speed will fluctuate rapidly and cause a saw tooth pattern on a waveform. This happens because the torque converter is slipping and sticking rapidly, essentially engaging and disengaging and allowing the crankshaft to speed up and slow down. Usually, think is felt and no codes are set. Sometimes torque converter codes are set and only very rarely a misfire code will set, but it is possible and I have seen it. In fact, I've seen false misfires from broken engine mounts. Things like sticking ujoints can cause false misfires, anything that speed up/slows down the crankshaft.

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