Sometimes after I've been driving my truck for awhile and park it, it tries to stay running even with the key out. It sounds like its trying to turn over and usually keeps doing that till it catches. Then it just revs up and dies. It runs fine other than that and it only happens when i've been driving for an hour or more. i was wondering what makes it do that and if it is a major problem that needs fixed. its a 79 f150 ranger with a 351 modified.

thanks

 

This is a common problem associated with an ineffective EGR system designed for these motors, its referred to as 'dieseling'.

Removing a non-functioning EGR system and advancing the timing 1-2 degrees to compensate may help, but be forewarned if you live in a emissions testing state that the vehicle will likely not pass.

 

will it hurt my truck if i leave it alone?? that fix is a little out my skill range, i really don't know a whole lot =/

 

leave it in drive or gear when you turn the ignition off, ( stall the engine ) then put it in park.

 

Actually it is referred to as RUN-ON.

Dieseling is that "marbles in a bag" sound that diesels make from Pre-ignition.... a much different problem .

Your engine is running on because there is unspend fuel being burned after the power is cut.


Check your fuel delivery & also spark plugs for being saturated with fuel and you ignition switch for being faulty and resending power to the coil.


https://www.ford-trucks.com/forums/6...ighlight=runon

 

It probably won't hurt anything if you leave it all alone... try keeping your foot on the brakes (if you have power brakes) when you turn the key off, this may help as well.

 

check your initial timing with the vaccum advance unhooked and plugged

 

Possibly to high of idle will also cause this to happen causing what Mil1ion explained

 

Wrong, run-on and dieseling are the same thing

http://en.wikipedia.org/wiki/Dieseling

Josh

 

yes run on and dieseling are the same, detonating is the marble in bag sound. Running rich and high idle,timimng and egr can all be involved. i personally have had a heck of a time trying to rid this problem myself after i built my motor up it always wanted to keep running after i shut it off. messing with the timing and fuel helped it alot but never cured it, so now, like its been mentioned, i park my truck in 3rd gear and let out on the clutch exactly as i kill it works every time

 

Yeah, I just learned to put it in drive when I turned off the truck. Mine would do it but not all the time, the few times it did, it scared the hell out of me.

I rebuilt the carb, changed all plugs, readjusted carb, redid vacuum and retimed it and it stopped doing it. Any one of those could have solved it for all I know, though I suspect it was the carb. I had quite a few leaky parts in the carb, everything was set wrong on the truck.

 

Out of curiosity, do you mean it never shuts off and keeps running, or it tries to restart? My '74 pulled a new trick a couple of months ago when you turned the key off, the guages cut ff, but the engine kept running-never missed a lick. That turned out to be the solenoid on the fender.

 

wiki is basicaslly the same as here .

People from all over the world use different terminology.

see that non-Wiki definition I posted on the other thread


To me Dieseling is that un-mistakable sound made by a diesel engine being accelerated ....much like that Pinging/Pre-ignition/pre detontation sound coming from a gasoline engine ....because the timing is off or the Octane rating is too low for it.

 

If you shut it off and it just starts chugging and sputtering, and even in really bad cases it'll start itself back up again, check for vacuum leaks first. Another cause can be the idle speed is way too high.

 

Had a similar problem in one of my old trucks it had a 400 the distributer was bad the drive gear to the shaft on the distributer was oblongated so it had slop causing some major timing issues. But it also had a tach in it and you could see that at variuos load changes in the engine the tach would fluxuate up and down.