DIESELING?

[DA]

i have 2000 stingray with a 4.3 mercruiser. the motor is dieseling everytime i shut it off. i have only had the boat a month. previous owners bought it new and only put about 20 hours on it. what adjustments need to be made to cure this. (1st time i/o owner) thanks for any info.

 

[12Footer]

Re: DIESELING?

Does this motor "ping" at all when you gun it under load also?<br />If so, your problem is low octane.Go up one grade and see if problem goes away.

 

[DJ]

Re: DIESELING?

MSA,<br /><br />Not uncommon for 4.3's. Several things to check and do.<br /><br />1. Check timing.<br /><br />2. Check idle speed.<br /><br />3. Decarbonize engine using GM-Top Engine Cleaner. It might not be called that anymore, but any GM dealer will know what you are asking for.

 

[Trent]

Re: DIESELING?

Try higher grade fuel.

 

[ShafferNY]

Re: DIESELING?

My Vote is for the timing.

 

[petryshyn]

Re: DIESELING?

decarb the engine, then adjust to proper idle speed. Check plugs for proper heat range.<br /><br />(timing is not an issue once the key is turned off)

 

[Spidybot]

Re: DIESELING?

Schematic,<br /><br />have to add, that if timing is severely wrong the plugs may become glowing hot hence ignite the air/fuel even after the the ignition has been turned off. Same symptom as if running way too lean.

 

[petryshyn]

Re: DIESELING?

Some increased in combustion chamber temp is possible from retarded timing.....true, but that much late timing would result in a power complaint long before an idle issue, especially on a watercooled (160deg) 4-stroke)<br /><br />Timing gets blaimed all too often. Over-advanced timing usually results in high idle speed. Once the timing is rectified, the run-on disappears. The reason for run-on was simply the increase in idle speed, but timing takes the "wrap" <br /><br />A cool running 4-stroke that is idled for long periods also has a tendency to carbon up. This carbon build-up can glow, causing detonation (dieseling) once operated hard and returned to idle.<br /><br />So many reasons, and so little time during lunch break!!!

 

[ShafferNY]

Re: DIESELING?

If the timing is advanced to far the spark ignites the fuel too late and leave some unburned fuel. If the engine is warmed up, combustion chamber temperatures can ignite the unburned fuel even though there is no spark, hence "Dieseling".<br /><br />Besides, what would it hurt to check it?