The PCM/Sea Maxx 350 in my boat seems to have gotten louder at the exhaust on one side. It sounds like there's something going on with just one cylinder. The sound is almost unnoticeable – someone else might not even hear it – but I notice it because I just know what this motor "normally" sounds like.
Anyway, at first I thought it might be a burnt exhaust valve or seat, but in discussing it with a friend, he suggested it might be a stuck/deflated lifter.
I put some Marvel Mystery Oil into the crankcase (and also the intake) to see if that might pump up a dirty lifter but I don't notice any difference, yet.
Can anyone give me any tips on how to diagnose this? I have a stethoscope and a compression tester, and I should probably buy a vacuum gauge (would that tell me anything?) ...
2000 PCM Sea Maxx 350 w/ 310 hp
throttle body injection
raw water cooled
Thanks in advance for any help.