Daily Boater
New member
So I need some help please. I have a 2002 Mercruiser 5.0MPI S/N-0M331599. The boat ran great up until the fall of last year when Inoticed a fluctuation of power above 1300-1500 range that accompanied whatseemed to be a misfire, popping or pre-detonation. I figured it was bad gas. Itwas the end of the season so I drained the tank down as far as I could and usedan external tank to winterize after changing the water separator. This spring Idecided to move to 100% zero Ethanol fuel 93% octane. I filled up. The problemfrom last fall was still present. Not only that but after a few minutes ofrunning close to full throttle the engine shut down. Had a hard time keeping itrunning and after less than 2 min of running I got an alarm and the boat seemedto go into limp mode. I broke down and took it into the dealer where it wasdiscovered Cyl. 5 & 7 were at 0 compression with cracks in the pistons andon Cly #1 at 120 PSI (the lowest still reading) and the piston appearing acidwashed. Cyl #8 was 180 PSI. Didn't remove the head to inspect Cyl 2-8 but aborescope showed similar appearances to #1 in Cyl 4 & 6. So I R/R'd thelong block and now I am breaking in a new Motor. Long story short, I fixed theproblem but still have a cause. The motor is running Lean. I haven't even beganto advance past 1800 RPM's in fear of repeating the damage. At R/R I also r/r'dFuel Injectors, Cap/Rotor, Water pump and impeller. During troubleshootingyesterday, I returned the original Fuel Injectors back to the motor just toeliminate the new ones from the equation. No improvement. Spark plugs indicatea lean engine. Note all sparkplugs removed from the damaged engine looked finewith exception of 5 & 7 which the electrodes were melted. So I need helpgetting this problem under control before I damage another motor. Please help!!All indications, fluid levels appear good and no alarms have been present. Newengine has aprox. 1 hr 40 min. first hour of break-in was performed on landwith flush muff. The 40 min was on water on and off 5 different times. FuelPressure is 34-38 PSI, I also ran with a remote fresh fuel supply and a newwater separator/fuel filter with no improvement.