Engine alarm

[jwclbi]

I have a 1998 225 EFI Merc with a three alarm system, overheat, low oil, and water in the separator. Everything is operating fine, not running hot, plenty of oil, and separator is new. As well there is an inline 10 micron separator to pick up water before the engine separator. What the engine is doing is at low speed and idle, after warm up, the engine will miss and the alarm will make one beep at exactly the same time, for a split second. Then continue to run fine. As well once on plane and through full throttle it runs perfect. I disconnected the wire from the engine separator thinking it was triggering the beep but that didn't help. As well traced a couple wires that led to one of two micro computer boxes mounted between the spark plugs. Any thoughts? Thanks