Hi all,

I own a 1981 f100 w 300 6 cyl. automatic.It will start just fine but when you turn the key off it stays running. The only way to get it shut down is to leave it in gear with for on the brake and try and stall it.
Is it the ignition switch or something else?
Thanks in advance

 

I would spray the ignition switch in the column with penetrating fluid first. See if that helps.

 

Welcome to FTE

When you say 'turn the key off and stays running" is it running really ruff or just like you never touched the key and running smooth?
Did this just start or been this way since you got the truck only a few days / weeks ago?
If just started and had the truck a long time when did this start, after any work was done?
When was the last tune up done?

If I had to guess it runs ruff when you turn it off.
If so this is what we call dieseling, fuel keeps burning without any spark.
This can be caused by a few different things.
First and most common it idle sped too high, check and lower to factory spec, thinking 650-700 maybe?
Turning off in gear lowers the idle speed so it may not diesel.

Hot spots from carbon or wrong spark plugs. Because you have a carb fuel can still be pulled into the motor and if there is something hot to fire the fuel it will keep running.
If plugs and idle speed is right get the motor up to normal temp and with a soda bottle full of cold water bring the RPM up to say 2500 - 3000 RPM and pour the water into the carb.
Thing is you dont want to stall the motor but enough that it takes the water. The cold water hitting the hot carbon breaks it down and it goes out the EXH.

They are the things that I can think of to cause run on, idle being too high is what I would check first.
Let us know what you find and if it helped or not and we can go from there.
Dave ----

 

Dave, I have owned it for years but it has been sitting for a couple of years now. Before it acted normal. We I said when I shut the key of it keeps running,it runs like I never turned the key off. I have tried the cold water thru the carb but it didn't change anything

 

So your saying, you could drive the truck as normal after turning the key to "off" ? If the steering didn't lock.
I'm guessing the switch is getting stuck.

 

Have you done any wiring lately? Or added a newer alternator? Added a switch for the ignition?

 

I am siding with MAX that the IGN switch could be the issue. Dirt and old grease could be hanging it up.
I cant remember the problem I had with mine but I pulled the switch and sprayed it with electrical contact cleaner & lube and its been fine.
Dave ----

 

I'm adding lube the ignition switch to my "to do list"

 

No I haven't

 

I haven't tried driving it when this happens, guess I was a little freaked out over it not shutting off

 

Disconnect the battery and then check the ignition switch. Make sure it's not loose. Maybe it's only loose in the off direction. There is a way to set it if loose. It's down at the base of the steering column. You want it tight and adjusted properly.

 

I'll check that out, thanks

 

When you turn the key from Run to Off, what happens to the heater fan and radio? Those are on separate circuits, controlled by different poles within the ignition switch. If the fan and radio remain on, you've probably got a loose switch or external linkage problem. If the fan and radio turn off, the problem is likely confined to a bad switch.

 

I don't know the answer to that question. I haven't paid attention to the heater fan or the radio.
I'll have to go back and look, thanks

 

I have an update. What I talked about before was from memories from 7 years ago. Well in the last couple of days I started getting it ready to run. While doing that it came back to me that once it got warm and you went to shut it off it would diesel terribly. That's what it's doing now, it will diesel for 15 to 20 seconds then it would make a noise which sounds like it's coming out of the carb almost like a backfire thru the carb, but not quite. I've ordered some stuff that's supposed to remove carbon.
Is there anything else I should try? Tia