www.iFourWinns.com

When I bought the boat it had AC MR43LTS spark plugs. Today I replaced them with AC R43TS because that's the plug that was listed in the Volvo repair manual I ordered from ebay. After installing them I started the engine and it ran like crap. Idling was rough and it was even hard to start. Now I'm wondering which spark plug is the correct one. The main difference I noticed between the two plugs is that the MR43LTS has twice the threads than the R43TS, and therefore must penetrate farther into the cylinder.

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Thanks,
Ben

1998 258 Vista 7.4Gi Duoprop

Time to survey the damage.
Your spark plugs don't have much clearance between the electrode and the piston top. With longer plugs, they were probably coming in contact...ie hard to push piston against stationary spark plug. Hence, runs rough as the plugs are damaged. Hopefully you didn't run it long enough to damage the pistons, or get pieces loose in the cylinder crapping up the walls or valves.
Pull the plugs out and inspect for signs of damage. If the electrodes are just flattened, consider yourself lucky and get the proper match to whatever you've been running for years. If any electrodes are broken off/missing, suck up your pride, open up the wallet, and take it to a professional.
Sorry...I hope it's not all that I fear it is.

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Walt B
"Debt-Charged"
Black '07 H210SS
6.2L Bravo One turning a 21P HIFive
Wakeboard Tower with Perfect Pass Stargazer version
Missouri River; Kansas City, Mo.

The new ones (R43TS) I installed are shorter than the old ones. If any damage would have been done it would have happened during the last two years. Seems to me that if these shorter plugs are not the right plug it's because the spark didn't get far enough into the cylinder.

_________________
Thanks,
Ben

1998 258 Vista 7.4Gi Duoprop

Gotchya, misunderstood your details.

Your right, the short plug may not even be getting the spark into the cylinder. Talk to your dealer, see what plug they use/recommend for the application.

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Walt B
"Debt-Charged"
Black '07 H210SS
6.2L Bravo One turning a 21P HIFive
Wakeboard Tower with Perfect Pass Stargazer version
Missouri River; Kansas City, Mo.

Dealer told me to use whatever was in there since I didn't have a problem before. We'll see what happens!

_________________
Thanks,
Ben

1998 258 Vista 7.4Gi Duoprop

Please don't shoot the messenger... but are you sure you got the wires back on the right plugs?

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Mike
2005 Four Winns 230/240
VP 5.7GXi/DP
1998 F-150 XLT
Boat Pic

Everything is back to normal! I replaced the plugs again today with the same ones that were in before and engine runs smooth. I did make sure that I only took off the one wire for the plug I was replacing. I do get a little nervous when I replace the rotor and cap, even though I label each wire. Thank for all the advice.

_________________
Thanks,
Ben

1998 258 Vista 7.4Gi Duoprop