Hi, I am trying to get help identifying (at a high level) what MIGHT be wrong with my boat so that I can intelligently describe it to my mechanic and discuss it with them. I do not intend, nor do I have the tools or time to fix this myself but I want to know a little more about what could be the issue(s). So I'm looking to be educated. The attached video from my phone, shows the motor and the sound it is making. Please turn the sound ON. This is a 2001 Mercruiser 5.7 EFI Engine: 2001 Mercruiser 5.7L EFI (Throttle Body Injection) Serial Number: 0L680772 with an Alpha One Gen II Outdrive Serial Number: 0L861805. I was going about 25mph when suddenly the motor started making this sound., like a choo-choo. The sound speeds up based on RPM but the pattern is consistent. I was in a river channel and dropped immediately to idle speed to get out of the channel to anchor until BoatUS towed me in. Please listen to the sound. It's hard to tell for sure but I think it's coming from the left side of the engine from the perspective in the video. A friend, who lives on the other side of the country and can't see the boat, has rebuilt his boat with the same engine/outdrive and he thinks it could be a loose spark plug and/or bad head gasket, maybe? He says from the nature/timing of the sound, it seems like it's an issue on only one cylinder. For the short time (10 min) it was idling until I anchored, the only "symptom" was the sound, no overheating or apparent oil leak was noticeable. If you have links to service manuals, videos, or potential diagnosis, etc. that would also be educational for me, I would appreciate that as well. Please see the attached video. Thanks in advance. I'd be happy to learn from you.
