305 diesels after shut off

my 81 305 is dieseling when I ahut it off. after 3-10 seconds later it does. but afrter i kill it it sputters and such. whats up with that?

Have you serviced it lately...oil/filters/plugs and wires/check the timing? Is there a water temperature gauge in the truck and is it working properly? What does it say? If all of the above is already done, and your water temp is in the proper range, it could be carbon build up in the combustion chambers that's causing pre-ignition. When the carbon build-up gets hot, it'll keep the engine "firing" even after you shut off the ignition. Since this is an '81, that's probably your problem.

also check for a rich idle mixture, and EGR valve,if it is not closing it will
contribute to carbon build-up in combustion chambers

I would check the operation of the auto choke. If the oil pressure powered switch has died, indicated by the choke light staying on with the engine running, the switch is likely the culprit. The coil may not be getting the current necessary to heat up, causing the choke, and the fast idle to stay engaged. Ray

this is one i haven't heard got more info???

my 305 did the same thing for a while.
the easiest fix is to adjust the timing. it fixed my problem.

if uve checked all the things listed above i would say its the timing. has the motor ever been opened up? if not the timing chain on that motor has most likley streched and has thrown the timing off. normally it takes more than a streched timing chain to cause this prob though, if its streched enough it could jump a tooth on gear causing it to be out of time. if u are going to go to the extreme of taking the front off the motor i would go ahead and put in a new cam and a double roller chain and sprocket set. might be good to check the bushings in the distributer also( especially if its the factory unit).