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Old 07-25-2010, 06:57 PM   #1
Lt. JG
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Default '99 1800sr w/3.0 mercruiser - engine doesnt like being turned off!

Hello, i have a '99 1800 sr with the 3.0 mercruiser alpha1. At times, when i turn the engine off it will continue to run (when i say continue to run, its real rough as if would be starved for fuel or something) after about 2 or 3 seconds it will eventually turn off completely. Anyone heard of this or have a quick fix ideas- Im auto experianced but not marine. More details if it helps would be* it runs perfect on the water* doesnt start as quick as i would expect it to(cranks over to long) but have never had another i/o to compare with. Thanks for any advice/help in advance.

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Old 07-26-2010, 12:50 AM   #2

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timpy...this is called dieseling and the engine can ingest water into the cylnders ...this engine is often found with this there are a few questions we need to ask you....
1)when was the last time you tuned it up....plugs,points(if required),plug wires, distr. cap..rotor...clean the flame arrestor?..
2) do you let it cool down some before turning it off??
3) are you using the correct octane of gas??

all of those items can affect dieseling..


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Old 07-26-2010, 01:27 AM   #3
Lt. JG
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Tks SP- as far as last tune up im not sure- i've only had the boat for 2 months- i was told it was up to par on its servicing but who knows for sure- i don't let it completely cool down due to people constantly reboarding the boat and the ladder is directly beside the prop.-I will let it idle for a few seconds and then kill it- i use 87 octane, i wasn't sure what it recommends.
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Old 07-26-2010, 12:52 PM   #4

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As SP said dieseling can be death to the engine (there seem to have been a number of posts on here about dieseling just recently).

Dieseling is a symptom and you'll have to figure out what the problem is - most likely though it's the 87 you are using. Try 89. If the tank is already full then dump a bottle or two of octane booster in there. You might also try shutting the engine down while the drive is still in gear because being in gear lowers the idle speed a little by placing a little drag on the engine.

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Old 08-04-2010, 09:11 PM   #5
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I have had three I/O's - 1 3.0 4cyl and 2 4.3 V-6 - and all have had the same issue.
All were corrected by using 91 octane, and in recent years, an ethanol treatment additive.
The one that has worked best for me is "Startron" which is also purported to be an octane booster.
If that doesn't work - my advise would be have the plugs and the timing checked.
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