When installing a cam, the misfire timers need to be desensitized in the tune, otherwise they will constantly roll over false misfire counts. Usually a misfire will feel obvious, as a break up under load, or loss of power. We can also tell this by reviewing a datalog. Under heavy load (PE) the mixture will be rich. On a stock o2 sensor this will ideally read roughly between 880 mv and 920mv. For reference 450mv is close to a perfect mix of fuel and air and less than 450 mv is lean. The o2 sensor doesn’t measure how much fuel is in the exhaust but rather how much oxygen is in the exhaust. It’s a bit more complicated than that but that is a simple overview. When a miss happens unused oxygen goes out the exhaust. This shows up LEAN on the o2 sensor. Therefore a miss will show up as a low spike in the o2 sensor graph. See above graphic of an HP Tuners datalog, showing a misfire on Bank 1. Note the o2 sensor (purple) dropping out lean.
