Truck Stays Running With Key off.

Bad ignition?

 

check the solenoid or the wires around them. i have had the solenoid to go bad on a pickup truck and cause it to do that, might be the problem.

 

I heard once if I leave the brakes set, put it in gear and release the clutch it shuts the truck off pretty quick. Heard it from a buddy, no first hand knowledge of course....

 

I had an old Mercedes Diesel once (300D) and on several occasions it would not shut off when the ignition was turned off. There was a mechanical valve assembly under the hood that you'd have to push to shut off the flow of diesel. Under normal conditions a vacuum solenoid would shut off the diesel when the ignition was turned off.
Anyway, don't know if the big rigs are somehow fundamentally different, but a diesel requires no ignition to run. So, when the ignition is turned off, something must activate to stop the flow of diesel fuel. It is not like a gasoline engine that requires an ignition system to run.

I'm a wannabe, am I missing something here??

 

That's true for the mechanical engines, but the electronic engines need electricity.

You would have to remove the ignition switch and use an ohmmeter to test the leads. Either the plug or switch is marked, or you have to contact Freightliner to find out which terminal does what.

Disconnect the batteries first. On the switch, there should be a batt terminal and an ign terminal. With the key off, the circuit between batt to ign should not be connected (no electricity to ign). With the key on, they should be connected (electricity to ign).

Make sure you try several times because a faulty key switch can sometimes work, sometimes not.

 

you have a bad ground. one time my truck would not turn off with key. was ground at the starter. it came loose out of crimped end. check all connections at around starter area & all main hot & ground cables,wires, connections.

 

Are referring to the fuel delivery system, which would make sense? By design, diesel engines need no "ignition" system, pressure is built up inside the combustion chamber and "igniting" the fuel/air mixture happens by rules of physics, not by a spark as in a gasoline engine. so the term ignition is what confuses me here. However, they do need some method of having fuel delivered into the cylinder. Is this the "ignition" system that's being referred to? My old diesel had mechanical injectors, I could easily see electronic injectors and electronic controls.

Please do not take what I am asking as any kind of sarcasm or anything like that. I am simply confused, desire to understand and am therefore asking questions trying to understand it. Thank you for your help.

 

Your ECM is fried. Happened to me once at a dealership. Went in to get a bunk heater fixed. They didn't disconnect the batteries before they started to work on it and arced something somewhere pretty hard. Had to wait 2 days for a new ECM out of St. Louis.