Engine run-on.

[bryanshaffer]

I have a Mercruiser 190HP, 6 Cyl on my boat and unless I let the boat idle for a few minutes after cruising, the engine will continue to chug and run after I turn the key off. Sometimes it can be for as long as 20 Seconds. I am pretty good mechanincally, but I don't know where to start. Any help would be appreciated.

 

[Walt T]

Re: Engine run-on.

Causes of dieseling:<br />Idle speed too high, engine temperature too high, Poor fuel quality or too low octane, excessive carbon build up on pistons and valves, the nut behind the wheel.

 

[Bondo]

Re: Engine run-on.

DieselWalt,<br />Ya Forgot Advanced Timing....

 

[Walt T]

Re: Engine run-on.

That has the same effect as raisng cylinder temps and speeding up idle. The advanced timing in and of itself does not cause it because once you turn the key off there is no more spark. You do bring up an excellent point Bondo, the basics should definetly be checked first.

 

[bluewater19]

Re: Engine run-on.

Mercury has a service bulletin on this subject with the 4.3 vortec. Check timing, check idle speed and use 89 octane minimum. The vortec motors have higher compression than the pre 1996 motors. Also I noticed my motor only runs on after I have been running it hard for a while. I took it in to the dealer and they gave me the same line they give everybody... let it idle for 30 seconds to 1 minute and then shut it down. They also said this tends to happen more on boats with tight engine compartments. I went with plugs 1 range colder and my motor hardly ever runs on anymore.

 

[bryanshaffer]

Re: Engine run-on.

Thanks for the help. I knew it was something relatively basic, just didn't know what it was.

 

[ndemge]

Re: Engine run-on.

just rebuilt the 350 in my van..... had that problem. for a few weeks, I would just put it in reverse when I shut it off, that would put a little strain on the motor and no more diesel.<br /><br />... Dropped my idle from 1,000 to about 850 rpm and fixed the problem.<br /><br />(freshly rebuilt engine, don't want it to idle really low yet)

 

[dmorley]

Re: Engine run-on.

Run a compression check. I did everything in the Mercury service bulletin and my 4.3 still dieseled. Compression check showed a range of 90lb to 165lb of compression--indicating something is seriously wrong. Machinist is going to pull the engine this week and I'll let you know what he found.

 

[LubeDude]

Re: Engine run-on.

one thing everyone forgot to mention is that with no fuel it wont run on! If a carburated engine there is usually an electric solinoid that holds the carb open when the ignition is on, if it fails and is stuck in the open position that could be the problem, with fuel injection dieseling usually happens if you have a leaking fuel injector along with the other things, You have to have a heat sorce IE Carbon or hot plug or????