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1:34 AM
Folks, I've got an OBD II diagnostic report, which shows misfires in cylinders 2 and 4.
Replaced spark plugs, the misfire codes went away.
It made me wonder, how does the ECU detect misfires?
 
hey there @Pᴀᴜʟsᴛᴇʀ2 and @NickAlexeev, how're things going?
 
 
6 hours later…
8:02 AM
@Shalvenay hi! Gdo is Garage door opener? One of those awkward crossover topics that could be here or could be on DIY. As you're talking about integrating it with the car, I think it's on-topic here
@NickAlexeev a combination of things I think, but probably mostly from the unburnt fuel in the exhaust, plus the slight fluctuations in crank rotation speed.
 
 
3 hours later…
11:32 AM
@NickC GDO = garage door opener, yes
 
 
2 hours later…
1:54 PM
@Shalvenay - I think as long as the question is confined to the operation/disposition of the vehicle side, the question would be just fine. If the question were about the GDO side, that'd be better suited for DIY ... IOW: I think you're just fine.
@NickAlexeev - I think it depends on the manufacturer and how they engineer their solution, but I think @NickC is pretty much right: it involves the crank rotational speed, how the ECU "listens" to the engine, and probably other things to determine which cylinder has an issue. Sounds like an interesting question for the site :o)
 
 
5 hours later…
6:32 PM
@Pᴀᴜʟsᴛᴇʀ2 because of interest: the knock sensor isn't involved?
 
 
1 hour later…
7:43 PM
@Martin - I would think it could be, but I really don't know for sure.
Realistically, I think the answer is "all of the above" ... meaning, they probably use all the sensors (or as many as they need to) to recognize a misfire event.
 
 
3 hours later…
10:43 PM
@Pᴀᴜʟsᴛᴇʀ2 posted
 

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