Help needed! I was running the boat (1991 weekender 280 w/mercruiser 5.7l v8s) at 3000 rpm and all was fine, when I suddenly heard the engine start banging-not knocking, but a banging sound coming from the port engine. This was about 20 minutes into the trip, running on plane for about 15 minuteS, when rpm began fluctuating. It went from 3000 down to 2500, then up to 2800, etc, so I aborted the trip and went back to the marina on 1 engine.
Engine runs fine at up to 2100 rpm without the banging, and idles fine; problem arises when I power up. Not knowing what the issue was, I didn't bother to power up again.
Fuel line was clean, so it wasn't a gas issue. Someone suggested that the engine might have gone into guardian mode-do the early models have that mode, even? Any help appreciated.
