Hello, need some advice, I have a 93 Mercury 175 EFI 2.5 , it had the 225 promax ECU added, boysen reeds, light weight flywheel, high compression performance heads, bobs oval tuner, sportsmaster low water unit with 30 pitch mazeco prop.

It has performed flawless for 5/6 years and number 2 piston ended up burning the temp sensor came on as number 2 is beside the sensor and the boat died in water, i restarted boat, ran for 5 minutes and did it again, the fuel pressure is perfect with only 2 psi of leak down, the injectors spray well with no signs of dirt, trying to understand what took place, is it possible it was over propped as it would only turn 5400 RPM when wide open and could that have caused detonation? All other cylinders are ok except 1 other piston that shows light signs of detonation starting.
The pistons were factory cast.

Any Thoughts? I appreciate any help