Kohler ECV870 misfiring

[ILENGINE]

It sounds like a condenser issue on an old points type ignition system. I don’t see it in your diagram but does the ignition system have an ignition capacitor? I replaced mine two times before I got one that didn’t fail after a few minutes.

Engine is EFI so the fuel pump, ignition modules, fuel injectors , timing is all controlled by an ECM.

 

[TobyU]

Yes, it was misfiring as you can see from the rpm display. Typically it would idle 1500-1550 rpm but as the video shows it dropped to the 1300's, and when the deck is engaged with the mower setting still it typically runs between 3300-3400 rpm but with the o2 connected it was dropping down to 2800 rpm. I did not notice any black smoke when it started misfiring and the smell was more acrid rather than rich.

An RPM reduction doesn't mean it's misfiring 100%.
I guess we could get specific on how the definition of misfiring but it normally means when something is running fine on all cylinders some are most of the time but occasionally or every few seconds etc one of those cylinders stops firing either completely or mostly. It usually comes and goes.

While this can affect engine rpms, it's usually not drastic.
It's usually just a slight roughness or a burble.
In fact, a small air-cooled twin engine like on the average riding lawn mower can start and run on one cylinder and still be within a couple of hundred RPMs of its normal operating speed or be right at it's normal RPMs if it's not under a load or once the load becomes consistent.
It's only when you put a load on it like engaging the blades or even if you're sitting there with the blades on as soon as you drive into grass that makes it drop significantly on the RPMs.

A far more common cause of RPMs dropping and engines even stalling out would be fuel starvation which really isn't misfiring at all unless one cylinder gets the fuel taken away a little bit earlier than the other and then it comes back so technically that would be misfying but in normal use, when you start to starve the fuel from an engine, it doesn't really start to misfire other than it just stops firing altogether.