Weird question of the day: I have a '70 Skylark with a 455 and HEI distributor. The HEI is fed from a wire connected to an "accessory" terminal in the fuse box. When you turn off the key, the motor continues to run perfectly. But, when the key is off, that accessory terminal goes dead. The motor should turn off, as well. The terminal shows dead until I turn the ignition on, when I turn the ignition off, it goes dead again. To kill the engine, I can unplug the wire from the fuse box and the engine quits. I don't quite understand how it can keep running when the feed wire is dead, why disconnecting an already dead wire would make any difference. Thanks for any ideas. Warren Senior Electrical Engineer (in my own driveway)
MSD explains this when installing one of their 6AL boxes. They give you a diode (?) that installs on the 4th wire on the box on the firewall that allows current to only flow in one direction. I think they call this condition "run on". I'll dig the instructions out of the garage tomorrow and verify this info. I have, occasionally, the same problem with my car, which has the 6AL. I haven't installed their "fix" as it is very rare.
Have you tired metering the wire with the igniton selceted off and car still running?? possible you have a hot short somewhere feeding it power.... I had this on my 71 GS one time. It would keep running with ignition off, then when you stepped on the brake pedal the engine would die!! Turned out to be the cruise control switch on the brake pedal had fallen apart inside so the contacts form the two seperate circuits crossed. The cruise power was fed from the igniton position on the fuse block and would feed back through that switch until you stepped on the brake pedal. later Tim
TimR, good suggestion, but this feed wire is all by itself. Due to the HEI, it has a wire just for that.
Check to see if you have an IGN or IGNITION terminal on the fuse block. If so, hor in run and start only, should feed the HEI correctly. What you are seeing now is votage feedback through the circuit you are using. What the diode does is stop voltage feedback from the exciter circuit in the regulator. Which design alternator do you have? Remote or internal regulator style.
Yes, a diode only lets voltage flow one way, but it is not a type of transistor. A transistor can be thought of as two diodes wired together; not allowing current flow in either direction unless you apply a voltage to the point where they are connected to each other (the base). A diode is like a one-way valve. A transistor is like an electronic switch. Sorry, don't mean to be picky. Just wanted to the chance to do something other than ask a question for a change.
Why does that go to the accesory? Why not ignition? I have the same setup, but my car isn't here...long story but I had two operations this week and I can't drive. Maybe I can look this weekend if they take all this plastic out of me and I can get off the pain killers...
And, a thyristor is an electronic gate for currect to pass through, activated by a side voltage source. Whart does all this have to do with a diode in a charging system?
Actually, the wire is plugged into the "ignition" terminal. The alternator has an external regulator. Any new ideas? And if you're talking diode speak, it mean nothing to me. Also, IgnitionMan: You converted my Buick 350 distributor about 6 weeks back. Excellant job, super quality, fires immediately, thanks again.
There has to be a feedback into that circuit that stays energized when the key is turned off, then. Usually, the charge light has just the right amount of resistance to stop the backfeed from the regulator/alternator. This allows the alternator to stop charging, circuit goes cold, engine stops. The diode does virtually the same thing for the later model internal regulator alts, when it is placed cathode twords the alt, wire number 1. Same may have to be done with the remote regulator to stop the circuit from backfeeding when the key is turned to the off position. I haven't worked on the remote regulator systems much, don't know exacty where the diode would go on them. For remote regulator systems, the way the light works is, key is powered up, 12 volts to one side of the bulb. alternator not spinning, regulator not seeing charge voltage, light off, regulator grounds the other side of the filiment. Alternator spinning, regulator excites the stator to make it into an elecrtro-magnet, which produces voltate, regulator sees voltage and changes light wire from ground, light on, to positive voltage, light off. When charge light is on, bulb is grounded thru regulator, light off, same refulator shows positive volts in the light wire. The backfeed problems come from the charge light wire on the ignition switch having more circuits attached to it, and feeds those circuits after the key is turned off.
I have had this problem too You dont need a diode, just try another terminal The problem is that the terminal you have connected the HEI to now is fed from the alternator (Look for voltage with the engine running and the ignition OFF you will see what I mean) In short, find the switched terminals in the fuse box and try them one by one (Fastest way is to have the engine running and then turning the ign off and on at each terminal until you find one that actually goes off)
Here's the latest- with the HEI wire connected to the ignition terminal in fuse box, when the engine is running and you turn it off, the terminal is still hot. The charging lamp in the dash comes on dimly. The only other terminal is the accessory terminal. It goes dead when the key is in the start mode, so that won't work. Somehow I need to get the alternator to stop charging when the key is off. We've narrowed it down somewhat, that's been helpful. I can always be e-mailed directly: reno1@continet.com
NTE-116. NTE, manufacturer, 116, rating. Cathode, the end with the silver band, goes twords the alternator terminal on internally regulated alts, don't know on externals, as I always replace them with an internal reg alt. NTE-116 is under 75 cents just about every place.
I added the diode mentioned above. MSD recommends putting it in line on the brown "#4" wire, on the external regulator. I did, and the engine still runs when the key is off. I was told to unplug the brown wire for a test, which I did, and the engine still stays running. With the brown wire disconnected, there should be no output from the alternator yes/no?
When installing HEI in my '72, instead of hooking wire into fuse box terminal I followed advice in Car Craft to search the loom of wires running up the steering column for a heavy gauge wire that has power only with the key on and splice into it. Works fine without a problem. Something you could try.
I did fix it, finally. It was true that while the engine was running, it was powering the electrical sources that are normally "switched" via the key. So, with the engine running, you turn the key off but the electrics still have power. Thus, the engine keeps running. The culprit? Previous owner (I just got this car) had the alternator hooked up the wrong wires. Even though it charged the battery, it was hooked up wrong and feeding the electricals. Fortunately for me, I have two other '72's to compare with. Thanks for the ideas. Warren
