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Merc misfire

I have a 242 with 5.7 efi engine and bravo 3. The engine generally runs rough almost as if it's misfiring unless I add a fuel stabiliser with the fuel. Should I have to do this every time I fill up or is there another issue I should be aware of?! It had a full service including plugs, leads and cap in August but still runs rough without the additive.

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    F1100F1100 Member Posts: 292 ✭✭✭
    What additive are you using exactly? Is it a water remover? or a stabilizer?

    Perhaps its just coincidence when you add the additive?

    How much are you adding to your tank, and how large is your tank?

    perhaps its just water in your fuel.
    1993 300 FIESTA VEE TWIN 5.7L ALPHA GEN 2
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    Michael TMichael T Member Posts: 7,227 ✭✭✭✭✭
    Are you running ethanol or 91 marine (non-ethanol) gas? Do you have a water separating fuel filter or in line fuel filter? Has either (if present) been changed? Did it run rough before the tune-up. Suspect wiring - remove one at a time. Each time a wire is removed the revs should drop. If one is removed and nothing happens maybe a plug or wire or damaged cap.
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