Dieseling after

[prc03sx195]

I have a 2003 4.3L V6 with a carb and was wondering why after I am running slower speeds for any length of time and turn engine off the engine will diesel for a while. Are there any adjustments on the carb for this? What causes this?
Thanks

paul

 

[Knightgang]

Re: Dieseling after

Carbon Buildup. The carbon gets hot and after you shut the engine down, the hot carbon continues to try to ignite the Fuel/Air comming into the piston.

Do a de-carb and change the plugs...

 

[Chris1956]

Re: Dieseling after

Paul, That is an unusual problem. Most(I had thought all) of the time you will get dieseling on the 4.3 after a high speed run. The cure was to idle a few minutes in neutral, before shutting down, to allow the engine to cool.

You might check the temperature of the engine. Sometimes the impellers get a bit worn and don't pump good at slow speed. Sometimes the thermostats get a bit wacky.

 

[Fishermark]

Re: Dieseling after

You also need to check your idle speed. If it is set too high you will experience the problem as well.

 

[ziggy]

Re: Dieseling after

can't find s/b 97-17 on line anymore. but it may be relevant to you...
basically it says.
engine dieseling or running-on. models covered mcm 4, v6 and v8 w/ carb

1. type of formulation of gas available in the area
2. typ of boat and its engine compartment vent system
3. outside air, inside engine compartment air and engine coolant temps
4. how quickly the engine is shut off after running at cruising or higher rpms
5. how the boat and engine are operated
6. engine idle rpm set to high
7. wrong heat range spark pulgs or spark plugs w/ deposits on them
8. deposits in combustion chamber.

suggestion to minimize run on.

item 1-3 can correct or reduce most of the run on problems. letting any engine idle a min. or 2 prior to shut down is desirable. this helps the engine normalize @ idle rpm before being shut down.

1. be sure engine idle mix, idle rpm and ign. timing are correct. w/ tb IV ign. setting idle rpm as low as possible can help stop run on.
2. adj. throttle cable barrel so that the carb throttle lever returns against the idle speed stop screw every time the remote control throttle lever is returned to neutral. idle.
3. idle engine 1 to 1.5 min. before truning key off after running at cruise or higher engine rpm.
4. try a different brand of regular fuel or try som premium fuel
5. increase idle mix by 1/8 turn 'richer'
6. go to next colder heat range spark plugs,
7. v6 & v8 only. install a 140*F tstat.

 

[EddiePetty]

Re: Dieseling after

Ziggy got ya' dead on this time !!!!!!

Items 1, 2 and 3 are, indeed the most effective at eliminating run-on.
IF your engine compartment is excessively restricted, the addition of a second bilge fan, BLOWING INWARD (and switched separately) will help normalize engine temperatures prior to shut down (also helps prevent vapor lock in real hot weather).
FWIW....Ed in 'ol Virginny

 

[CJCJ]

Re: Dieseling after

Adjusting the throttle cable fully to the idle stop fixed the dieseling situation on our new boat, Sea Nymph w/ 4.3L OMC.

 

[wired1236]

Re: Dieseling after

My 4.3L does (did) the same thing. My idol is in spec so the Volvo mech told me to run a higher octane fuel. I was already putting in 89oct so went up to 92 and it stopped. I also now make sure to idle the boat after a hard run for 15-30 sec after I stop. Don't have the problem any more unless the marina only has 89 or less octane gas.

 

[boatingnva]

Re: Dieseling after

Only time my Merc 5.0 does this is when I run a higher octane gas that my marina has. If I remember and fill up with regular at the local quick stop before hitting the lake, I dont have that problem.