klossfam
New member
Hopefully a fair question but at 159 hrs (I've owned for 51 and did the 100 Hr Service) I started to get a misfire at all throttle positions. I thought fuel but seemed good and has spent it's whole life on 90 Ethanol Free.
I checked the obvious and replaced the water sep filter and primary fuel filter. I then pulled each injector plug one at a time but still a rough idle one each individual injector. I then did the spark plug check and very obvious (see below) that cylinder 3 was the issue. I replaced the plugs and it immediately ran perfect at all RPM ranges.
My question is, what are the possibilities of a simple non-firing aka bad plug vs an underlying cause? Has always ran perfect up to Labor Day when the rough running started. I won't have much run time left in 2026 to test more as the season is short on the Great Lakes.
I know these NGK plugs were legit (a lot of counterfeit plugs out there now) and they were perfect from hrs 108 to 159. I did test the resistance of the #3 plug and it was the same as the others (in the normal range). Thoughts?
I checked the obvious and replaced the water sep filter and primary fuel filter. I then pulled each injector plug one at a time but still a rough idle one each individual injector. I then did the spark plug check and very obvious (see below) that cylinder 3 was the issue. I replaced the plugs and it immediately ran perfect at all RPM ranges.
My question is, what are the possibilities of a simple non-firing aka bad plug vs an underlying cause? Has always ran perfect up to Labor Day when the rough running started. I won't have much run time left in 2026 to test more as the season is short on the Great Lakes.
I know these NGK plugs were legit (a lot of counterfeit plugs out there now) and they were perfect from hrs 108 to 159. I did test the resistance of the #3 plug and it was the same as the others (in the normal range). Thoughts?
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