396/425

Im not much on motors. I know just enough to be dangerous. But can anybody explain why my engine will sometimes diesel (run on) a little after i turn key off. Not all the time. Sometimes.

After38Years

Probably carbon buildup in the combustion chambers. It gets hot and ignites the fuel-air mix that still gets sucked in as the engine rotates down after the ignition is turned off.

Powershift

What is you idle RPM?? Too high a curb idle will cause this.

Larry

396/425

I believe it was 900. I just got it out of mothballs so to speak.. I think 900 .....it seemed a little high. I didnt have time to play with it much. I got sidetracked. Good point. Maybe that was it.

Frankie the Fink

First thing to check is too fast of an idle speed...you could get off easy...

69427

Dieseling is almost always caused by too high of an idle speed, or too retarded idle spark timing.

396/425

Thanks all. I think i raised idle last season at end of season. Ill drop it down to 700 800. Im pretty sure it was 900 950 now that i think about it

DansYellow66

If the timing is a bit retarded the tendency is to make up for it by raising the idle setting (thus opeing up the throttle blades to where they are up near the top of the idle transfer slots). Perfect recepie for dieseling. Set the timing to spec (which would raise the idle) and then back off on the idle speed adjustment will often cure it.

If the car has an aftermarket cam in it with more duration and lift, the rear (secondary) throttle blades may need to be opened very slightly at idle to compensate and allow the primary throttle blades to be closed a bit more.

MikeM