Spark Plug Replacement

1132MM

1132MM

Member
Aug 1, 2010
184
Wantagh, NY
Boat Info
2004 Sea Ray 280 Sundancer
Engines
Twin 4.3 Liter Mercruiser w/Alpha One Gen 2 Drives
I have a 2004 280 Sundancer with twin 4.3 MPIs. This is going to be my third season with her. I want to replace the spark plugs and was wondering if it’s a difficult job. I have read online two different spark plugs: Iridium NGK ITR4A15 or AC 41-993. I’ll probably replace whatever plug is in there because the boat ran great. Looking for some tips. Thanks
 
I've done it on my twin 350's... not too bad, allot of blind work to get to a few of them. Nothing had to be removed on mine. Also changed them on my buddies twin 350's, but his are Horizon so I had to remove one hose on each motor to get to a plug.
 
1132MM said:
I have a 2004 280 Sundancer with twin 4.3 MPIs. This is going to be my third season with her. I want to replace the spark plugs and was wondering if it’s a difficult job. I have read online two different spark plugs: Iridium NGK ITR4A15 or AC 41-993. I’ll probably replace whatever plug is in there because the boat ran great. Looking for some tips. Thanks
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If clearance is tight, you could grind down the outside of the spark plug socket to gain some extra clearance or try using a regular 12 point 5/8” deep socket instead of the spark plug socket. They are thinner and could also provide extra clearance around the exhaust.
 
A short piece of rubber tubing slid over the porcelain will help aligning that plug in the cylinder..
 
Thanks for all the replies. I will have the check the previous owners maintenance records when they were changed last. I was just concerned I might have fouled them when I was fogging the motors winterizing them.
 
Yes, used Marvel Mystery Oil to fog the motors.
 
Guys do NOT fog MPI engines! If you're stabilizing your fuel all season there's no need to fog. If you read the Mercruiser manual it says to formulate a winterizing fuel mixture and run it thru the fuel system by disconnecting the fuel line and hooking it up to a remote tank. I did this for years but after speaking with my mechanic he said don't bother, stabilized fuel is good enough. I've been doing this now for ten years without any problems or fouled spark plugs.
 
1132MM said:
Yes, used Marvel Mystery Oil to fog the motors.
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Yes, probably should be changed out. As @Brite Idea mentioned, Mercury recommends a premix to winterize/store the engines (basically a mix of 2stroke oil, heavy stabilizer and fuel). I run it through using a premixed remote tank. But as discussed, for just a couple of quick months a double dose of stabilizer to the tank if probably enough and then run through the systems before shutdown for the winter.

-Kevin
 
Lots of stories of plug wires crossed and poorly running engines. Make sure you label each plug wire on painters tape and draw a diagram for reference.
 
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