My 1997 4.3 V6 Mercruiser engine continues to run/sputter for 5-30 secs after we shut it off?

Question

Some white smoke also

Answer 1

2 things that would cause dieseling  thats what its called

1st  timing is off

2nd gas octane is to low  try running it with high test  see if it goes away  if you dont want to spend the extra money see if you can have a mechanic r****d the timing

Answer 2

Not sure about a boat but this is caused in a car by bad gas. Add some fuel treatment to your gas in the boat and see if this helps. Also have you been running ethanol added gasoline through it? If so I would add ethanol treatment to it(removes ethanol)...That ethanol just dont agree with boats.

Answer 3

carbon build up in the cylinders.  glowing bits of carbon ignite the fuel/air mixture, so the motor continues to run, but timing is off (cause the spark plugs aren't firing), so it's sputtering like mad.

Add Seafoam to the tank, a lot of it.  It'll smoke like crazy, but'll clean your engine up.

Answer 4

I have the same engine as you and the same problem as you. I use only alcohol free Shell Premium Gold 97 octane gasoline and it's serviced regularly by reputable mechanics. When I asked them about the run-on, they said that it's not a serious problem and was just an issue that some Mercs had as they aged. Get it checked out but I wouldn't worry too much about it.

Answer 5

All of these answers are partly correct.On this engine from

1997-2003 Merc had a problem with the carburetor.To meet

California EPA standards they had to set the idle jets accordingly.This in conjunction with the timing was causing the run-on.Some of these engines could be fixed by adjusting the carb and timing but some of them could not.In order to fix them we had to re-jet the carburetor.At the time it was a warranty issue but will probably not be covered now.Hopefully

you will be able to fix it by just resetting the carb & timing but if not I would be glad to help.Just post a new question and I will assist you.Good luck.