87 caprice problems turning off

[87BoxClassic]

When I turn my car off it still tries to run it's a 305. It usally does it for 10-30 seconds. Has anyone else had this problem? It doesn't do it too often when I put super gas in. But it still does it every once in awhile with the super.

[MagicRat]

Run-on occurs because your engine is using a compression ignition cycle, like a diesel engine, when you turn the key off. Chances are, the combustion chambers have lots of carbon build-up which increases compression ratio and provides nice, red-hot pieces of carbon to ignite the fuel-air mixture.

A decarbonizing would help the situation. I have had success with a spray can of combustion chamber cleaner, sprayed down the carburetor when the engine is idling and hot. Some people have used Seafoam or just dribbled 10 oz of plain water down the carb (a very slow dribble!! Don't pour it in!!)

It's a bit unusual for lower compressions engines like yours to do this. But in the 1970's it was common. There were lots of high-compression engines from the late '60's being run on the dishwater that passed for gasoline back then.

I once had the throttle stick wide-open in a '77 Jeep. When I turned off the key, the engine ran-on strong enough to drive the car at 30 mph. No fun!

[j cAT]

Originally Posted by 87BoxClassic

When I turn my car off it still tries to run it's a 305. It usally does it for 10-30 seconds. Has anyone else had this problem? It doesn't do it too often when I put super gas in. But it still does it every once in awhile with the super.

if your engine is running too rich you will get this problem..can also be from oil burning as well...

with running on high octane the combustion chambers run cooler...

I would make sure carb is adjusted correctly including the anti stall/run on solenoid, timing , correct plugs, and any vacuum leaks...make sure the engine has no vacuum leaks first then check for proper carb adjustments,,use a vacuum guage...

also the vapor cannister control valve for defects...this little guy if broken will suck gas right out of the vapor line into the intake, causing a rich condition..

excessive carbon WAS a problem back in the pre middle 1980's...I used to use a product called "regaine" this removed the combustion chamber deposits because of the fuel at that time was not burning correctly with all the cleaning additives...the fuel blend in the later 80's was changed so after 1985 I never required this product..the fuel today burns very clean so you have a defective componet causing this...

my vehicle then was new, less than 20,ooomi and it would ping and run on until I used this product every 3,000mi...but like I stated this ended in 1985 when the fuel blend changed never did that again for 360,ooomi...