Ok, here's the deal. I replaced a frozen carb, swapped out a dead battery, and finally got the truck running after a few weeks of working on it. Now, when i shut the truck off, the engine keeps sputtering. So, i have turn the key back to the start position, wait a few seconds, and then shut it off again. This has been happening for two days now. First i thought i flooded it with fuel, but i let the truck sit all day and all night and it still did it this evening. It's not my daily driver. Any ideas??? Thank you in advance. 1979 K5

 

How old is the gas in the tank? Also, how is the timing?

The correct term for what you are experiencing is "dieselling'. It could be a result of running on fuel of insufficient octane. In this case, as with knocking and pinging, the fuel is being ignited by the heat of compression, rather than by the spark plugs (which are not firing if the ignition is turned off).

If you gas has just gotten old, then you can either drain the tank or tweak the throttle right before turning off the ignition until you get some better gas into it.

Also, if you are running on some lower octane stuff, you should retard the timing a smidge. Has the engine been pinging while under light, moderate, or heavy load? If it has, then you need to retard the timing, but this won't affect the dieselling effect because the ignition should shut off when you turn the key off.

Is the motor original, or has some work been done to it. I believe that in '79, the 350 v8 had 8.5:1 compression. That is more than friendly enough to run on 87 octane, but don't rule out a bad tank of gas either.

You might also want to try a bottle of ISO-HEAT in your gas tank to absorb any water that could be in there.

Good luck and if this information has helped you, please let us know!

 

Thanks for the info SWARTLKK. The gas is fairly new, i just filled it a couple of weeks ago. I think it may have worked itself out, it seems to be shutting off like normal. Chances are, you're right, the older gas that was in there may have been the working it's way out causing the dieselling effect. thanks again for reply