Good Morning.

I had an issues about a month ago where I would start the truck (302) and warm it up real good and then turn the key off and the truck would continue to run, or it would sputter out like it really wanted to keep running. I ordered a new ignition switch, thinking that something in there was not working correctly. since i replaced that switch, it hasn't given me a problem since - until last night, we went out for icecream, got to the shop, parked and turned the key and pulled it out of the ignition.. the truck was still on. I tried many times to mess with the key and see if i could get it to turn off - no dice. The truck sat there and ran the whole time we ate ice cream..

Any ideas?

I'm thinking short somewhere under the dash? Ignition control module?

Thanks

 

Perhaps, but it could be down at the fender mounted starter relay as well.
Do you still have the standard style starter fro these trucks, or has it been upgraded to the modern PMGR style with the piggyback solenoid?

Either way, when it happens again, pop the hood and remove the Brown "I" wire from the starter relay. It's one of the small wires facing outward on the small posts. One is the Red w/blue stripe "S" wire that actually starts the starter spinning, and the other is the Brown "I" wire that gives the ignition a little extra boost during START.
If the relay has failed and power is getting to the Brown wire then it could conceivably keep the engine running. I'm really not sure how it would also get to the Ignition Control Module's power wire, but there might be some feedback path there somewhere.

Hope it's that simple. But it rarely is!

Paul

 

Side question regarding the ignition module. What color is the "grommet" (wire strain relief) where the wires come out of it?
Does it have two plugs, or three?

Paul

 

I will have to check when I get home.

Thanks for the reply.

 

My 77 F250 300 straight six has done the same thing about two or three times. Since I have a 4 speed I just put it in high gear and choke it out. It's gotta be a feedback situation somewhere. Unfortunately it hasn't done it at home so I could have the time and equipment to troubleshoot it.

 

To me that sounds like dieseling - that's when the spark plugs get too hot, they are hot enough to cause ignition without a spark. Which will keep the engine running if they stay hot enough. Caused by running way too lean usually. It can also be caused by lots of carbon buildup on the pistons. Carbon flake on piston gets hot, turns red, is hot enough to ignite the fuel mixture, bam, dieseling.

But maybe something electrical too

 

well, it happened again this weekend. I got out of the truck and pulled the spark wire off of the coil. it stopped immediately. So, with that i would have to rule out dieseling.

As far as the ignition control module, I cant tell the color of the grommet, its all painted black over there. Has 2 plugs coming out of it. pretty sure its an aftermarket unit.

 

Check to make sure you have a ground-strap running from your engine to the firewall. It's usually run from a bellhousing-to-block bolt to a small bolt on the firewall.

My truck was missing this ground when I got it, and the main symptom was the starter would stay cranking when I'd release the key. But one time I went to turn off the engine, and it kept on running till I pulled a battery cable or maybe it was the coil wire. It only did the engine run-on once, but it used to do the starter run-on somewhat frequently. Once I added a ground cable from the engine to the cab, it's never done any of those things since.

If you have anything tapped into the small red wire which goes to the "S" terminal on the solenoid, that could cause the starter to run-on.
I'm not sure about the "I" terminal, but it seems easy for me to assume that if you have some accessory tapped into the small wire which goes to "I," that it might cause an engine run-on condition.

 

awesome, thanks! I will check into those things. I actually had the engine crank on condition it would crank and crank untill it killed the battery and smoked the starter solenoid... did that a few different times. Thought it was in the ignition switch. replaced that and it hasn't done that since - but has done this engine on thing a few times.

Ill check into it. I don't believe that i have any accessories tapped into the small wires of the solenoid, but i will double check.

 

Did you replace the old solenoid/relay with a new one after the smoke? If so I would never overlook the fact that many of the new ones are crap and can give you fits trying to track down issues.
The good news in your case though, is if this is a new one and it's still working after a week, it's likely better than most!

So many starter relays fail right out of the box that we're beginning to think that the bad ones just get put back on the shelf and re-sold many times. It's so bad that it's probably one of the more popular (infamous) discussions on the forums.
To the point that many of us recommend new starter relays come from the junkyard rather than the parts store. At the very least get a Motorcraft or other known-good brand, and pay the price. Some have hunted down certain ones that say "Made in the USA" on the box, and I paid 60 bucks for a Volvo/Penta Marine relay hoping that the USA made and marine certified version will be reliable.

Anyway, sorry for the long-winded story, but that was by way of warning to not overlook the recently replaced parts anymore, when hunting gremlins.

Paul