Daily Boater
New member
So I need some help please. I have a 2002 to Mercruiser 5.0 MPI S/N-0M331599. The boat ran great up until the fall of last year when I noticed a fluctuation of power above 1300-1500 range that accompanied what seemed to be a misfire, popping or pre-detonation. I figured it was bad gas. It was the end of the season so I drained the tank down as far as I could and used an external tank to winterize after changing the water separator. This spring I decided to move to 100% zero Ethanol fuel 93% octane. I filled up. The problem from last fall was still present. Not only that but after a few minutes of running close to full throttle the engine shut down. Had a hard time keeping it running and after less than 2 min of running I got an alarm and the boat seemed to go into limp mode. I broke down and took it into the dealer where it was discovered Cyl. 5 & 7 were at 0 compression with cracks in the pistons and on Cly #1 at 120 PSI (the lowest still reading) and the piston appearing acid washed. Cyl #8 was 180 PSI. Didn't remove the head to inspect Cyl 2-8 but a borescope showed similar appearances to #1 in Cyl 4 & 6. So I R/R'd the long block and now I am breaking in a new Motor. Long story short, I fixed the problem but still have a cause. The motor is running Lean. I haven't even began to advance past 1800 RPM's in fear of repeating the damage. At R/R I also r/r'd Fuel Injectors, Cap/Rotor, Water pump and impeller. During troubleshooting yesterday, I returned the original Fuel Injectors back to the motor just to eliminate them from the equation. No improvement. Spark plugs see to indicate a lean engine. Note all sparkplugs removed from the damaged engine looked fine with exception of 5 & 7 which the electrodes were melted. So I need help getting this problem under control before I damage another motor. Please help!! At this time it runs good u to 1100 RPM's with no alarm present.