Forever running

MY '70GS 455 runs so well it sometimes doesn't want to stop! Sometimes when I turn off the key it keeps running. Other things seems to turn off, such as power to power windows, radio, etc, but the egine keeps purring along. I run the key from off to on and back many times and sometimes this will work, not always. Last night I had to pull the wire from the fuse panel labled "ignition", then it stopped and I could hear the relay behind the drivers' side kick panel disengage at that time. I'm not sure if that relay turned off due to pulling the wire, or what? Someimtes I put the car in gear and then shut it off, this seems to help too, but not always. Suggestions?o No:

 

Larry, Thanks for your reply. It is definitely not dieseling, I've experienced that in other cars in the past where it keeps running even if you pull the plug wires. This is absolutely normal running. In fact I do have an MSD 6AL box. Where does the diode go? I'll dig through my literature on the box and see what it says. I'm electrically inclined, so I'm curious about why the diode may be necessary. Diodes are somtimes used to allow a line (or wire) to be pulled low while not affecting other things on that wire (diode logic).

Another consideration..... I have noticed sparks coming from my shift linkage when I start the motor, just as if there is no ground connection between the engine and battery. My battery is mounted in the trunk, neg side of batt is connected very securely to the frame of the vehicle only. I added a heavy gauge wire between the frame and exhaust manifold. I measure 0 Ohms between engine and frame, but I still get sparks from the shift linkage when I crank the engine. Just don't ask me what happens when this sparking occurrs with my freshly rebuilt carb that unbenounced to me had a sticky float! Ka boom! really! Thank God for fire extinguishers, I'll always have one in the garage. A very reputable Q-jet rebuilder had just gone through it, somehow he missed that...... I guess no one bats a thousand. Anyway, anything to think about in regards to engine not shutting off and possible poor ground connection to the engine? I thought that by moving the gear selector to somewhere besides park (column shift) that might possible allow for a better grounding throiugh the linkage becuase there would be less slack in the linkage making a better ground cennection, thus allowing the engine to recieve a better ground and then allow it to shut down. But I can't figure outhow that would have anything to do with the ignition, unless the MSD box is grounded to the engine, and not the frame......

 

Here is what happens when the engine will not shut down: the alternator is providing the necessary current for this box, (the MSD.) If you look at the wiring of the older alternator systems, the field voltage is controlled by the ignition switch, and turned on by that switch. The problem occurs when the ignition is switched off. The alternator, operating normally, now provides the voltage to the field wire through induction. The result is that the ignition, pulling significantly less current than the stock unit, now gets its current directly from the field wire, which powers the ignition. The fix, provided free by MSD for their users, is a diode, which acts as a one-way valve, allowing only current from the ignition switch to power the ignition. The alternator's current, blocked by the reverse biased diode when the key is off, is therefore blocked, killing the ignition. When the key is on, the forward biased diode allows normal current flow to the alternator. This problem was almost eliminated by the new charging systems, which control current to ground, rather than the supplied voltage. Ray

 

Ray, Many thanks! I got the info off of MSD's website on how to resolve this run-on problem. I'll give it a try!

 

Yep, the diode did the trick! Many thanks guys!

Steve