Hi good day. I bought a boat with a 4.3 mpi mercruiser in it. It were running fine no problems . But now it goes into limp mode after about 10 or so minutes and in beginning it did not back fire now it does . Took it to a workshop and they tested it and it came up with no faults on scanner. So I went pick it up and went straight on water started up perfect running smooth and then after about 10 min starts backfiring and cuts out on limp mode only running on 3 cylinder not 6. Called work shop up and mechanic recons he can't see any thing on scanner. Things I did . Change feul filter, 6 new spargplugs, check roter and dizy cap all good . Check the shift interup switchall good. Any ideas what to check next please. Low idle it don't back fire only under load in water. Outside with earplugs on it only goes into limp mode no backfiring .
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