engine won't shut off after warming up.

[agaldamez]

Engine seems to run very well. Temperature running 170 degrees, oil pressure running 70, full throttle is hitting 4800 rpms, with a speed of 47mph.

i have a 2003 rinker bow rider, with a 4.3 mercruiseer alpha one, gen 2.

After running a good 20 min, when i turn the engine off it stalls to turn off. If i turn the key back on the engine runs as normal.

when i do turn it off its stalls , the time frame is different, it could be 10 sec to 45 sec if I let it.

What could be the problem. Help Please.

 

[500dollar744ti]

Re: engine won't shut off after warming up.

Sounds like your engine is 'dieseling'. It is a symptom where the engine continues to run without a spark after the key is turned off, it only happens with carbureted engines.

It kind of feels like the engine continues to chug after you switch the key off, is that what's happening?

 

[agaldamez]

Re: engine won't shut off after warming up.

That is correct, chug is the right word.

 

[agaldamez]

Re: engine won't shut off after warming up.

how do i fix this???

 

[500dollar744ti]

Re: engine won't shut off after warming up.

Are you using low octane gas? Switching to a higher octane can definitely help. Check your timing, make sure it's set correctly. 170 degrees sounds a little high for a raw water cooled engine, has your impeller been replaced recently?

I won't lie, my engine does this from time to time, only after slowing down from a long run on a hot day, if it happens I turn the key back on and let it idle for a few moments then shut it off and it's okay. It never happens for more than a second or two though.

If you are using 87 octane, definitely try premium and report back.

 

[agaldamez]

Re: engine won't shut off after warming up.

I use non ethanol gas. i will try the higher octane.

how do i check the timing. changed my impeller this season but it did it last season also, just not as much.

 

[500dollar744ti]

Re: engine won't shut off after warming up.

Go to the adults only section stickied at the top of the forum where you will find the mercruiser service manuals, it will contain the info needed to check timing. You will need to buy or borrow a timing light to do so.

It is possible that vibrations over the years have caused your distributor clamp bolt to loosen and the distributor has rotated some. That would leave your engine improperly timed and could certainly cause the engine to diesel after turning it off.

 

[agaldamez]

Re: engine won't shut off after warming up.

will do. thanks.

 

[UNSUREBOATGUY]

Re: engine won't shut off after warming up.

Idle too high?

 

[dan t.]

Re: engine won't shut off after warming up.

Very possibly idle too high, or timing a little late, or carbon build up in the combustion chambers, or low octane fuel. Idle the motor for a minute after a run, some times that helps.

 

[Utahboatnut]

Re: engine won't shut off after warming up.

As stated idle may be a bit high(500-700)is about right. mine will do this as well even with the timing spot on new impeller etc. if however i let it idle for approx 1 minute before i shut it off it never does it. This is something you need to get fixed or try the idle down method dieseling can cause the engine to run in reverse right at the last before it shuts down which can suck water into the engine which is bad, very bad.

 

[nola mike]

Re: engine won't shut off after warming up.

Let the engine cool down before shutting it. Idle it for a minute or so.

 

[Lone Duck]

Re: engine won't shut off after warming up.

That is also a symptom of a lean mixture open jet 1/8 of a turn and check.

 

[agaldamez]

Re: engine won't shut off after warming up.

Not sure what lean mixture open jet means. what is 1/8 of a turn.
could you please explain. really appreciate it.

 

[thumpar]

Re: engine won't shut off after warming up.

What is your engine idling at on the water?

 

[agaldamez]

Re: engine won't shut off after warming up.

Can i do this running the engine with my water muffs or should i wait till i put it back in the water.