Mercury 175 HP 1994

by Ron B
(Eden Prairie, MN USA)

I have a 1994 Mercury 175 HP EFI outboard that has an intermittent problem where it seems to be dropping 3 cylinders. It is not reliably repeatable. I have taken it to a dealer 3 different times and they cannot get it to act up long enough to find any problem. The symptoms are that it happens when being started, it will accelerate slowly to a plane and run that way for a couple of minutes then it will suddenly kick in on all 6 cylinders and take off. While it is running on 3 cylinders it runs hotter than when it is running on all 6. It does not happen everytime it is started. It does not happen repeatably after sitting for several days of after being run and shut off. It has never dropped to 3 cylinders after running on all 6. Needless to say it idles poorly when it is on 3 cylinders. Compression on all 6 cylinders is good. The fuel system has been replaced. I feel like it has to be an electrical parts issue. Any ideas?