"Hey all. Just joined, was loo
"Hey all. Just joined, was looking for any similar noises of 4.3L Mercruiser after I ran our boat and heard a rattling sound.
Here's the story: new deckboat bought last year probably has only a couple dozen hours on it. Began taking the boat out on the water a month ago used most of the gas, added only 7 gallons to put some fresh gas in. Places on water were closed, one accepted the little cash ($20) I had and gave me some.
Well, yesterday I took the boat out and idled a few minutes while I put the canopy down. I noticed a loud rattle sound, figured it to be canopy supports hitting against each other. Wasn't... was in the engine compartment. Opened it up and isolated it (possibly) to the leftside valve cover.
In gear and throttled up a bit the noise quieted, more RPMs and it wasn't heard at all.
Went back to dock and drove to gas station for 10 gallons and STP fuel treatment (using partial bottle). Put out onto the water again, idled and nothing heard.
Conclusion: bad gas...? That's all I can figure it could be. Interestingly, the oil pressure was showing 60 when the noise occured. Read about 50 after the fresh gas. Overheated oil maybe, or something else? Water temp always said normal, middle of the gauge (when warmed motor).
Needless to say I'm going to check into this more next time.
BTW, AFAIK this engine with the 2V TKS carburator might not have any anti-knock adjustment (sensor?), but the Multi-Port Injection ones probably do. I thought that could be part of the problem, or rather an incapability to prevent such events-- if it is knock/ping.
Anyway, hope this is of some help to this thread. Not intending to hijack it, just seemed a similar situation.
Thanks for this message board, could prove a good source of info for me from the looks of it!"