1999 Mercruiser HI-Performance GM 377 EFI Engine Service Manual, Page 46Get this manual

1999 Mercruiser HI-Performance GM 377 EFI Engine Service Manual, Page 46

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TROUBLESHOOTING
Used Spark Plug Analysis Normal Condition Chipped Insulator Wet Fouling (Oil Deposits) Cold Fouling Overheating High Speed Glazing Scavenger Deposits Pre-Ignition Damage Reversed