350 gas - diesels when switched off

[dontoe]

My best freinds Chevy P/U diesels when he switches it off. He said it stopped when he switched to Mid-grade gasoline.

Never encounterd this type of problem before. What'cha think?

Found this in a search................is that it other than timing!

You might have an idle stop solenoid thats not working--its an electric device that sets the idle speed by pushing against the throttle lever on the carb--it jumps out and sets the idle speed when you turn the key on,and retracts when you shut it off,so the butterflies in the carb shut completely,making sure the engine shuts off.If yours lost power due to a blown fuse or bad wire to it,it wont idle--and you have to crank up the idle speed screw to keep it running.This allows the butterflies to hang open,and makes the engine "run on" or "diesel" when you shut the key off,you need to see if there is power to the wire on it with the key on--if not,check fuse and wiring.It could be the solenoid itself died also.Timing not adjusted to proper specs can cause this too,also too lean a mixture in the carb,makes it run hot,and a valve or carbon in the cylinders can get hot enough to "fire" the mixture just like the spark plugs would. I've had a few trucks with junk idle stop solenoids,I usually just crank the idle speed screw up just enough so it wont stall out in drive(automatic)and if it tends to "run on" I just shut it off in drive,or pop the clutch in 4th gear to stop it,but the right fix is to make it work again.The fast idle cam on the carb might be sticking too--that will do the same thing,so can the choke not opening all the way.

 

[diesel4me]

Sounds like me!

I think that was ME who posted that last year sometime!

Other than what that post listed,a valve or carbon deposits can glow red hot and ignite the fuel even when the spark plugs stop firing when you turn the ignition off...but if thats the case you will get pinging under load or acceleration too..and its hard on the pistons and valves when that occurs..

I'd say 90% of the time its timing too far advanced,idle speed too high,or the idle stop solenoid not working,( if it has one)-and someone turned the idle speed up to compensate,that encourages dieseling...

My 79 C10 has an Edelbrock carb,it has no idle solenoid--I turned the idle speed up slightly during the cold winter to prevent stalling--now that its warmer,its idling a bit too high,and it started "running on" after I shut off the ignition--I turned the idle speed down about 100 RPM so it idles at 700 RPM in drive--no more dieseling..Til I adjusted it,I just left it in drive and shut it off,it wouldnt diesel then either--but I almost forgot to put it in "Park" a few times--almost ran my foot over when it started rolling away!..

 

[big jimmy 91]

As was already said , carbon build up.

You can get some carb./combustion chamber cleaner from a parts store...
Or use the back yard method of pouring water down the carb when hot , just not so much as to hyro lock it(while reving it up,not allowing it to stall)
Cleaning or changing plugs is recomended after either method

 

[Z3PR]

Run a can of 44K through it and see if that helps.

 

[dontoe]

Thank you gentlemen!!!

 

[R72K5]

idle speed is too high, or timing is too advanced

one of the two is the cause 99% of the time

fix it ASAP,, it will start damaging the engine if you let it continue to occur,....