Originally Posted by quint
Originally Posted by clinebarger
#3 intake valve was moving @ 0.030" while #5 intake valve was moving over .500"...... …. Also asked a very good question that I honestly didn't have an answer for....."Why is the misfire intermittent"
Take this with a grain of salt, but I remember reading about a similar situation on an aircraft engine (I'm an A&P) and a few people with degrees far more expensive than my own said that the reason for the intermittent misfire is because on the cylinder with the wiped out lobe, there is enough lift of the valve to allow a small amount of intake charge in, but not enough to fire the cylinder. And not enough to exit the cylinder during the exhaust valve opening. Then over the course of three or four intake events enough pressure builds up to increase compression high enough to allow that cylinder to fire. Depending on the throttle opening this may be rhythmic or intermittent as the intake vacuum varies with engine load and throttle movement which in turn varies the amount of air actually getting into that cylinder.
Its not my theory, but it sounded fairly reasonable, at least to my level of expertise.
Funny you mention this--as I read about these MOPAR cam issues was wondering if they had the same supplier as Lycoming! I flew a light twin powered with Lycoming IO-360-200's during the early 2000's and I don't recall the number of cams we went through with those engines, but at least a couple for each engine (it was flown A LOT). Lycoming chalked it up to a bad supplier. Anyway, I recall that at full-power operations (take-off, climb) the bad (cam) engine would run like a swiss watch, but at reduced power it would miss noticeably--that always seemed counter intuitive to me. I'm flying a single-engine these days and consider myself much safer!