3.0L Mercruiser "diesels" at shut down

[reelman6]

I have a 2004 Searay 180 that has a 3.0L 4 cyl. in it. I bought it from a dealer used last year. From the beginning it occasionally runs-on (diesels) after shut down. I assumed that it was the timing, but that didn't help. When I took back to dealer, they said the carb had "junk" in it so they removed and cleaned. It was the end of the season and they stated that they made sure it didn't do it any more. I put a new fuel filter in it before I ran this year just in case it was dirty fuel. Although not as bad, it still does it intermittently. Back in the day when I turned wrenches for a living on cars, this was usually a bad throttle position sensor. I do not see anything like that on this carb. I think the only reason it doesn't do it as much is the fact that they turned the idle down so low. Any thoughts would be appreciated.

 

[rbh]

Re: 3.0L Mercruiser "diesels" at shut down

I read last week in one of the posts there is a service bullitin that deals with this issue, you just have to go and look for that post, as it has the link.
rob

 

[DrEvil]

Re: 3.0L Mercruiser "diesels" at shut down

Make sure your idle is set properly. Mine was a little too high and adjusting it down helped take care of the problem. I have also read that you need to idle it for a bit to get the pressure in the carb down.

 

[mylesm260]

Re: 3.0L Mercruiser "diesels" at shut down

on a fuel injected motor, when you turn off the key, you're cutting fuel and spark.

On a carbed motor, you're only cutting spark. If you get a hot spot in you're combustion chamber (piston/head) you could easily be "running on".

#1 first things first, on you're next tank, run better fuel (92 or better)
#2 consider using sea-foam to clean out you're combustion chamber
#3 consider adjusting you're carb to run slightly richer.
#4 consider pulling a degree or 2 of timing


After you've solved the cause of the problem, then you can go back to 87 octane fuel, I would not suggest running the engine too much with 87 octane until you resolve the issue, as you may be experiencing pre-ignition, which may melt a piston or destroy a head gasket.