1990 bayliner won(39)t shut off-gctid813443

[jm2494]

Hello I have a 1990 bayliner capri with a 3.0 liter mercruiser the issue I am having is when Irun it wide open for long periods at a time it dose not want to shut it off i turn the key off and it spits and sputters and shakes the whole boat then shuts off I was just wondering if there was a solution to this problem or if any body else has had this issue

thanks.

[TenMile]

Possible that your idle speed is set too high? Otherwise, try using an Octane Booster or run a higher octane fuel as that should eliminate dieseling.

[SomeSailor]

It's just dieseling... burn off all your old gas and get something a bit higher in octane. Sometimes an older motor with a lot of carbon build-up will make it worse.

[bhawes]

That is a common problem on the 4.3 Merc's., so I'm not surprised that the 3.0's also do it. After running at speed for any period of time, let them idle for 2-3 minutes, then shut them down. If the timing, fuel/air mixture, and idle speed, are all set correctly, the motor will then shut down.

[Pcpete]

What Bob said. Let the engine idle and cool things off internally. For one thing the engine will last longer. It amazes me the number of boaters that will warm their engines up before leaving the dock but are quick to shut them down while the first mooring line is still in the air from being tossed. Sometimes with both ends going to the dock.....then the entertainment factor goes way up.

[2850Bounty]

"jm2494" post=813443 wrote:
Hello I have a 1990 bayliner capri with a 3.0 liter mercruiser the issue I am having is when Irun it wide open for long periods at a time it dose not want to shut it off i turn the key off and it spits and sputters and shakes the whole boat then shuts off I was just wondering if there was a solution to this problem or if any body else has had this issue

thanks.

[color]blue wrote:
As suggested, your engine is undergoing what is refered to as "run-on" or "dieseling". This is extremely common with the carbureted GM 3.0L 4 banger!

Basically, when this occurs the conditions allow for contiued combustion without the need for spark ignition. In other words, when you turn the key switch to OFF (killing the ignition spark), the cylinders are still firing sporadically, causing the engine to continue turning over..... sometimes turning over in the oposite direction.

Causes:

.... poor octane rated gasoline

.... carbon build-up within the combustion chamber

.... higher than desired cylinder temperatures during shut-down

.... excessively lean low speed fuel/air mixture

Possible remedies:

....Run only high octane gasoline.

....Fatten up the low speed fuel metering.

....Lower the idle RPM to within OEM specs.

....Allow the engine to cool down some prior to shut-down.

....If feasible..... try to shut-down while in gear!

This has been and is an on-going issue for Merc.

I have not been able to understand why Merc has not resolved this by using a step-down solenoid device at the throttle shaft!

General Motors used a step-up solenoid in the early years as to increase RPM during AC compressor operation.

The reverse of this could be incorporated .................. KEY OFF..... throttle plates further close!!!!!!!

[/color]

.

[jm2494]

Ok I will give some octane booster a try, Could this also be why it is hard to start? It seems like i half to crank it over quiet a bit to get it to start.

[Chief_Alen]

How do you start your boat ?

Came back to edit :

Below post #2

http://www.baylinerownersclub.org/in...tarting#652263

If the run on doesn't quit after you tried my method, then maybe steam cleaning the inside of your engine is in order .

Want to know how ?