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Collective brain picking time:
A few weeks back i got a CEL (light) on my gasser at 80k. I have a cheapie reader, which came back as cylinder 6 misfire. Im due for new plugs soon, so i figured it was that. I cleared the code, but it was stored in history.

Maybe 500 miles later, same light and code. This time it wouldnt clear because it was reoccuring as i was clearing it. I should point out that i had zero symptoms, zero rough idle, zero change in mpg.

Not wanting to drive on 5 cylinders for fear of putting raw fuel into the cat, i made an appointment with my independant about 1 week later. When the day came, no light and no code in history (verified on my scanner too). We decided it was dumb to chase no code and no symptoms, and its 3k later and no reoccurance.

Two observations: 1 is that the pentastar has no plug wires, its coil on plug. I looked up the price, think it was about $70 each. Thats very reasonable if it ever needs them. 2 is that i asked how the computer knows which cylinder isnt firing. Apparently, the crank position sensor is wideband enough to sense a speed difference at the crank and derive which cylinder isnt firing. Neat.

My question is what might have caused this code? Normally i might say rain or high water, but that didnt happen. Radio interference? Could low alternator voltage cause it to misread or glitch? What non-ignition problem would cause the crank sensor to misread? Im going to ignore it until it happens again or presents a symptom, but im just wondering if anyone had any ideas.
 

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Plug fouled by carbon?-probably wont reappear- Marginal COP? will fail again when conditions are right, replace it and own a spare. (BTW my F150 had just this issue) Valve hung open, sticking? will probably reappear, compression test.
Best.
 
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