Engine will not turn off

[88 Doral]

Its a 2002 Stingray with a 3.0. When the engine is warm and I turn the ighnition to the off position the engine will stumble for a few minutes. I had overheated the engine on the last run of the season and the engine would not shut off. Turned off the ignition and put the battery switch to off.

 

[Scott Danforth]

your motor is dieseling. common on the 3.0 with incorrect ignition timing or wrong fuel. I also found them to diesel when skiing. dieseling can lead to the motor running backwards and sucking water. until you find the cause and correct it, leave in forward gear and key off.

 

[Bondo]

Ayuh,..... Welcome Aboard,.... It sounds like yer describin',... Dieselin', or run-on,.....

It can happen for a variety of reasons, motor heat, or a need of a Tune Up are the most common,.....

If the motor has been run hard, usually a minute idlin' will allow it to shut down,.....

It's pretty important ya fix it, as the last stumble of the motor ya hear, is the motor runnin' backwards, which sucks water into the cylinders, which is very Bad,....

So when was the last time it saw a full Tune Up,..??

 

[88 Doral]

your motor is dieseling. common on the 3.0 with incorrect ignition timing or wrong fuel. I also found them to diesel when skiing. dieseling can lead to the motor running backwards and sucking water. until you find the cause and correct it, leave in forward gear and key off.

Fuel as in running the wrong grade? Only seems to happen when the engine is warm.

 

[bruceb58]

Before you shut it down, idle it for a minute like Bondo says, turn on the blower during that minute and put it into gear as you are turning it off.

Is this doing this with fuel that has been sitting around awhile? If so, it's octane may be less than it used to be. Try using fresh fuel and/or a higher octane fuel next time you fill up.

 

[Silvertip]

Carbon build up in a hot engine can ignite fuel causing the issue as well as idle speed set too high. Cars of the era had anti diesel solenoids on them and with the reversion problems experienced on boats I wonder whey they weren't used. It is not like it cost a fortune to add one as it only involved the solenoid and a mounting bracket. The solenoid was adjusted to provide the desired idle speed. When the key was turned off the solenoid dropped out and the throttle closed completely. No fuel/air - no run. A bore scope or even a pen light through a plug hole can confirm if carbon is an issue. Sea Foam can take care of that as well.

 

[88 Doral]

I always let it idle down before shutting off. Its was getting progresivly worse all last season.

I have had the boat going on my fourth season. I have never done a complete tune up. I have changed the plug wires once and spark plugs every year. Plan on having the carb done this year, plugs, distributor cap and distributor rotor.

I was told it may also be a selenoid or relay on the carb.

Heading accross the border next week and was looking to order any parts that I needed to save on some shipping and brokerage fees.

 

[alldodge]

I always let it idle down before shutting off. Its was getting progresivly worse all last season.

I have had the boat going on my fourth season. I have never done a complete tune up. I have changed the plug wires once and spark plugs every year. Plan on having the carb done this year, plugs, distributor cap and distributor rotor.

I was told it may also be a selenoid or relay on the carb.

Heading accross the border next week and was looking to order any parts that I needed to save on some shipping and brokerage fees.

Do you have a TKS carb?

If so look at this
http://www.marinemechanic.com/merc/distributors/mercurymarine/sterndrive/tksdiode.pdf