79 not shutting off correctly
Thread Starter
Cruising
Joined: Mar 2008
Posts: 11
Likes: 0
From: Harrisburg Oregon
79 not shutting off correctly
I just got a 79 L82 that when I turn the key off the engine will run for 3 to 5 seconds after the key is off. Does anyone what might be the problem? I almost think someone tapped into the wiring some place and the distributor is getting a back feed for a few seconds.
Race Director
Joined: Feb 2005
Posts: 16,100
Likes: 17
This condition can occur for a multitude of reasons:
Built-up carbon in the ignition chamber can glow red after the engine is off, providing a mechanism for sparking unburnt fuel. Such a thing can happen when the engine runs very rich, depositing unspent fuel and particles on the pistons and valves. Similarly, non-smooth metal regions within the piston chamber can cause this same problem, since they can glow red. It has also been suggested that an improperly rated spark plug can retain heat and cause the same problem.
A carburetor that does not close entirely can contribute to running once the engine is off, since the extra fuel and oxygen mixture can combust easily in the warm piston chamber. Similarly, hot vaporized oil gases from the engine crankcase can provide ample fuel for dieseling.
Incorrect timing.
An engine that runs too hot or too lean may produce an environment conducive to allowing unspent fuel to combust.
An idle speed that is too fast can leave the engine with too much angular momentum upon shutdown, raising the chances that the engine can turnover and combust more fuel and lock itself into a cycle of continuous running.
Check your idle speed first...then go from there...
Built-up carbon in the ignition chamber can glow red after the engine is off, providing a mechanism for sparking unburnt fuel. Such a thing can happen when the engine runs very rich, depositing unspent fuel and particles on the pistons and valves. Similarly, non-smooth metal regions within the piston chamber can cause this same problem, since they can glow red. It has also been suggested that an improperly rated spark plug can retain heat and cause the same problem.
A carburetor that does not close entirely can contribute to running once the engine is off, since the extra fuel and oxygen mixture can combust easily in the warm piston chamber. Similarly, hot vaporized oil gases from the engine crankcase can provide ample fuel for dieseling.
Incorrect timing.
An engine that runs too hot or too lean may produce an environment conducive to allowing unspent fuel to combust.
An idle speed that is too fast can leave the engine with too much angular momentum upon shutdown, raising the chances that the engine can turnover and combust more fuel and lock itself into a cycle of continuous running.
Check your idle speed first...then go from there...
Melting Slicks
Joined: Oct 2006
Posts: 2,417
Likes: 336
From: Texas
my 79 L82 did the same thing for awhile, i found that it was the aux. electric fan, when it was running its a motor, when the key is turned off it turns into a DC generator, back feeding 12v, into the fuse box. until it slowed down enough to stop gen. power, then the engine would stop. it was supplying power to the hei distributor. ii unplugged the fan and the engine would stop as soon as the key was turned off.
i ran the fan power through a relay and that ended that.
i ran the fan power through a relay and that ended that.
Melting Slicks
Joined: Aug 2003
Posts: 2,135
Likes: 2
From: Dayton Oh
my 79 L82 did the same thing for awhile, i found that it was the aux. electric fan, when it was running its a motor, when the key is turned off it turns into a DC generator, back feeding 12v, into the fuse box. until it slowed down enough to stop gen. power, then the engine would stop. it was supplying power to the hei distributor. ii unplugged the fan and the engine would stop as soon as the key was turned off.
i ran the fan power through a relay and that ended that.
i ran the fan power through a relay and that ended that.
I did have the run-on issue after changing my distributor but quickly discovered that my timing incorrect.
