so, i have a 89 steiger craft with a 5.7.merc I/O  fi .  basically it is making a nasty clanking sound under load starting at about 1500 rpm all the way through 4,000. doesnt really do it when i rev under no load. sounds like a bad diesel. had a couple guy look at it and they said it was bad fuel, but when i hit it it has awsome power and jumps out of the hole like it has allways. from my little experience fuel issues would show with decreased power. i had about half a tank and i added some fuel stabilizer and octane booster aswell as filled her up with about 30 gals of fresh fuel. beed going to the same gas dock for the last 20 years. asked them if they had any issues and they said no of course. also a little background, i have been having an issue with the engine monitoring system, the alarm goes off started going off above 4,ooo and the gradually dropped down to 1500 and i couldnt even drive the thing. it moniters the oil pressure, watter temp and exhaust temp. my oil pressure guage was reading norm and water temp norm but i dont have a egt temp. so i replaced the impeller on the raw water pump and it went away for a little. them came back. some times but not allways. the alarm isnt going off right now while this issue is present. engine was replaced brand new in 03. any advice would help. also just to iliminate the fuel issue im going to grab a 5 gal fuel tank of premium and disconnect the filter inlet hose ( fuel feed line into filter) and run the engine on this fuel thus iliminating the boat tank to see if there is some issue there.??????