Engine remains running after key turned off

[mymach]

Hi All,

Just looking for a little trouble shooting advice here. My 1970 Mach 1 351 Cleveland wouldn't shut down today after turning the key off. Went to start it later, and the key worked that time.

Is this a ignition key switch probable or could something else cause this as well?

Thanks!!

 

[truck90278]

How did you get the engine to stop?

 

[mymach]

How I got engine to stop

Pulled the coil wire from the distributor. Even got bit!

 

[dennis112]

A malfunctioning starter selonoid will also allow the motor to keep running.

 

[302Rich]

Possible run on answer

If you're running an electric fan without a relay the momentum of the fan will make it work like a generator and it could backfeed enough juice to make the car run for a minute.

 

[iskwezm]

i second the solenoid

 

[truck90278]

It is possible that the solenoid is bad, my experience is when they go bad, either the starter motor won't crank at all (most common) or I have also experience the solenoid sticking in the closed position and therefore engagine the starting ALL the time in the flexplate/flywheel after the engine has started. Which quickly fries the starter. You may want to do a voltage chek with a meter to see if you have voltage to the coil/distributor when the key is in both the on and off position. Most vehicles with points, in the start mode only, bypass the ballast resistor and apply a full 12 volts to the coil/distributor for starting purposes. After starting, then the voltage should drop to 4-6 volts. If you have a continuous 12 volts at the coil/distributor, then stronger suspicion of the solenoid. If the key is off and you have 12 volts, try disconnecting the wire for the ignition from the solenoid.

 

[doug68hoss]

my advice is to unhook the battery cable until you get this potively figured out..and be careful even then...i have seen switches that you cant shut off be all kinds of hell to stop a electrical fire....
the last thing you want is alot of wiring going up in flames..these old cars are always making a smoke cloud under dashes and so forth..

 

[351carlo]

On a 70 the easiest way to have the engine keep running even with the key out is if the plug on boots that attach to the two studs on the starter solenoid are reversed.

One is red, one is green? (I'm trying to remember as I'm 20 miles away from my car). If they are reversed the car will continue to run and run and run.......

Been there, done that. 1970 Mustang w/ 351c.

 

[mymach]

Thanks for the advice guys. Funny this happenned following my replacing the solenoid with a brand new one. I'm quite sure I kept the wires correct on the solenoid posts. The red one is toward the front of the car and the green is toward the rear. This is also intermitant. I'll try pulling the wire next time this happens.

 

[351carlo]

See I had a way of remembering it.... red on right...... but I forget if it was while hanging over the fender or looking at it head on.

Someone will chime in with which way is correct.