496 Mag Knocking
07-04-2017 | 10:04 PM
#1
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496 Mag Knocking
Been a member for years but my first post. Thought I would give back a little since I only lurked in the past.
I have an '04 Formula 330ss (owned for 8 years and 480 hours) with twin 496 Mags and Bravo III's. For the last two years I have had knocking periodically between port and starboard engines, I wouldn't drive over 30mph because thats when the knocking would start but I didn't want to do damage... My main marina was told about this and he replaced my ECU for about $750... Last year I took it elsewhere because it wasn't fixed and after draining the tank and cleaning both fuel injectors and replacing some random parts the starboard acted normally but the port didn't ($2200). The port continued to knock at 3200 rpm+ and they wanted me to bring it back... My marina said it could be bad gas, I got desperate and found a thread about a knock on this forum. I was ready to sell her.
Thought it might have been an exhaust sensor then my Dad mentioned the spark plugs, "when did you last change them?" Hmmm Well I assumed when I did my tune ups it would be done... Needless to say, yesterday a mechanic buddy and I changed the AC Delco 41-983 plugs and found three bad ones (2 on the port and 1 on the starboard engines). You could literally rattle them and the electrode would hide like an ice cold dip in the pool.
Fixed!!! She is alive again and as good as new! No knocking and the beast is alive! My previous mechanics suck and I cannot believe they didn't do a simple google search. Either way I'm posting this in case your having a similar issue.
Cheers,
Mike
I have an '04 Formula 330ss (owned for 8 years and 480 hours) with twin 496 Mags and Bravo III's. For the last two years I have had knocking periodically between port and starboard engines, I wouldn't drive over 30mph because thats when the knocking would start but I didn't want to do damage... My main marina was told about this and he replaced my ECU for about $750... Last year I took it elsewhere because it wasn't fixed and after draining the tank and cleaning both fuel injectors and replacing some random parts the starboard acted normally but the port didn't ($2200). The port continued to knock at 3200 rpm+ and they wanted me to bring it back... My marina said it could be bad gas, I got desperate and found a thread about a knock on this forum. I was ready to sell her.
Thought it might have been an exhaust sensor then my Dad mentioned the spark plugs, "when did you last change them?" Hmmm Well I assumed when I did my tune ups it would be done... Needless to say, yesterday a mechanic buddy and I changed the AC Delco 41-983 plugs and found three bad ones (2 on the port and 1 on the starboard engines). You could literally rattle them and the electrode would hide like an ice cold dip in the pool.
Fixed!!! She is alive again and as good as new! No knocking and the beast is alive! My previous mechanics suck and I cannot believe they didn't do a simple google search. Either way I'm posting this in case your having a similar issue.
Cheers,
Mike
07-05-2017 | 12:32 AM
#3
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Joined: Jul 2011
Posts: 9,594
Likes: 45
From: Ft. Worth TX
there has been a few issues with these plugs. Also I would change the spark plug wires and double check your coils to make they are firing and properly.
The original Denso spark plugs were junk in these 496's.
The original Denso spark plugs were junk in these 496's.
