Misfire Module B

Hi Bill
I would have sent this last night, but after a hard day of troubleshooting, I was just pooped.  Talk about chasing our tail.  We tested all of the cylinders with a laser gun. #3 was a little cooler, as was the exhaust pipe, but only about 100 deg.  We used a timing light on all of the plug wires and all looked good, and we swapped plugs around as you suggested, everything remained the same.   My helper, Keith is a retired race car mechanic.  He asked how the compression was and I told him that it was excellent and that I always pull at least 4 blades through before each start; old habit from my C195 days.  So as I demonstrate, which was just after a hard shut down as it was really shaking, I had 3 super compression blades and one soft.  I did it again and it was still soft, and stayed that way for an unbelievable number of tries.  So we pulled the top plugs and ran a compression test, only to find that all were up in the high 70s, and the soft cylinder was gone again.  We pulled the valve cover on # 3 and everything looked good, even when pulling the prop through slowly.  We tried a feel test by manually  compressing the valve springs, but the lifter would take up the gap and now the cylinder had zero compression.  I started it and ran it for a bit and retested and found that the lifters self adjusted and the compression was back.  Talk about intermittent!!  If you remember, both plugs on #3 look clean as a pin, while all of the others are sooty.  Another tip is that I occasionally  hear a noise, particularly during warm up, which I thought was caused by engine knock due to misfire, but in fact is probably a sticking valve. 

I can't prove it because it is so intermittent, but I think that it is time to take things apart and investigate, unless you have a better way to be certain.  All of that electrical and carb chasing, and it looking like a mechanical problem.  I run exclusively on alcohol free 93 octane auto fuel, and have only used 100LL once while on a trip.  Are sticking valves common on these, and do you have any easy fixes?  Again, I am not positive, but I would bet a weeks pay on it, and when I look at all of the pieces of the puzzle, it fits like a glove.   Your thoughts.....Tom

Sticky valve came to my mind as I started reading your last post. What you could maybe try is spraying throttle body cleaner into the carb intake while idling the engine.

Thanks Bill, that sounds better than using Avblend in the oil like I was thinking of doing.  You know, CRC also makes and intake valve cleaner for direct inject engines. The idea is to spray it into the vacuum line, rather than a carb, which it doesn't have.  Do you have any personal experience with either. or am I blazing new trails??..Tom

You're Welcome, But that was Garrett you wanted to thank.

I had a line about checking compression in my last post but reconsidered and deleted it.

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An old boaters trick is to add 1 ounce of Two-Stroke Oil per 5 gallons (600:1)

This adds a little lube to the hot side of the cylinder and keeps the exhaust corrosion down.

If you try this trick do NOT use TC-W3 Marine Oil intended for water-cooled engines.

Use 2-Stroke Oil intended for Air-cooled engines, e.g. Chain Sawl, Snow-Mobile.

Okay Guys,  I Thought  I would update you on my intermittent mis and the intermittent loss of compression on a cylinder somewhere.  Still not sure which one it was.  After pulling #3 which was the only cyl  where the spark plugs looked clean, and cyl # 1 looked the worst while 2 and 4 weren't much better, a close examination revealed #3 is one healthy cyl. The combustion chamber looked super.  A little carbon, but no real buildup, just what I would consider normal.