Engine runs with key off.....

[Faulk21NG238]

I posted this in the electronics forum and didn't get a response. Im hoping someone here can help.

I have an 80 Malibu with a 383 stroker. The problem I am having is, when you turn off the key, the engine shuts off for a split second, then starts back up and runs for another 2-3 seconds. I originally told my mechanic about this, and he seemed to think that there may be something wrong with the ignition box. All of the wiring to the ignition box (original car wiring) is original. The car ran about 2 years ago (with a different motor, same ignition) and never had a problem. The engine is not running hot when it happens, somewhere between 180-200 (reading from the intake). Never does it while the engine is cold.

Cam is a Lunati Voodoo Duration 268/276, Lift .489/.504. Ignition is an MSD 6A (4-5 years old). Distributor is an MSD Pro-Billet Vacuum Advance. Timing is set somewhere between 32-36 degrees (wasn't there when the mechanic put it in time). Accel 7.5mm wires. AC Delco plugs.

I am at a loss. Anyone have a suggestion? Don't really want to shell out $200+ for a new ignition box if that's not the problem. May have given more information than needed, just trying to cover everything I know of.

Thanks for the help.

 

[Bonnewagon]

Do you have the diode in the alternator wire? If not the tiny amount of residual current can allow the MSD to function. You can read the directions online that addresses this point. the MSD is a capacitor discharge system with a voltage amplifier so even a fraction of a volt will run it. If the diode is there, it may be leaking voltage, but they are cheap enough. I go even further than this by installing an on/off switch in the battery line to the MSD with 10 gauge wire. They say not to but I have had no problems doing it.

 

[Faulk21NG238]

I assume you are talking about the wire that goes from the alternator to the battery? I converted my alternator from a 3 wire to a 1 wire, since then, the car has been doing this. That would make sense then.

I don't know much about electronics so I have a few more questions.

1. What does the diode I need to use look like?

2. Are you talking about putting a battery switch between the battery and the ignition box?

 

[Bonnewagon]

Here's a link to some good info. http://v8buick.com/showthread.php?207154-Needed-Diode-for-a-MSD-6AL-system And here is the MSD link- http://www.msdignition.com/page.aspx?id=3296It is a wire with a tiny drop of semiconductor that looks like plastic in the center, the colored bands are for the color coded rating. I used to get them at my local speed shop for a buck. I am reading that this is no longer so easy to come by, but Radio Crap may have it. It's a 100v/1a diode, you can go bigger, but not smaller. Then they said for a quick fix just yank the idiot light alt bulb and it won't run on anymore. That is *ss-uming you have the brown wire going to the idiot light. It is important to instal it correctly, a diode allows current to go in only one direction, and blocks it from flowing in the reverse direction. The switch I mentioned was in the big red power wire to the MSD box from the battery. I used a large marine grade switch, marine grade fuse holder, and soldered crimp ring connectors screwed to the switch lugs. Think heavy duty so you don't starve the MSD electrically. Why? Because the box is always "hot" wired to the battery. That is unacceptable to me.

 

[Faulk21NG238]

Ok, thanks. I am going to give that a shot. Someone also mentioned "dieseling". Any thoughts on that?

 

[Jshock]

If its dieseling then there is an issue with idle speed, and fuel delivery. Either too much fuel or just lean enough that it detonates when shut off and keeps everything rotating but not nicely. If it wasn't doing it before and you didn't tweak anything I'd be hard pressed to say that's what's happening. I'd follow the previous posts first because those MSD boxes can be the cause pretty easily.

 

[Bonnewagon]

I just re-read the first post. " The problem I am having is, when you turn off the key, the engine shuts off for a split second, then starts back up and runs for another 2-3 seconds" Hmmm. An MSD getting a trickle of voltage will KEEP the car running until you find a way to stop it, either electrical or fuel wise.(another good reason for the kill-switch in the red battery wire!) And dieseling is a pretty intense condition with hammering, clunking, chugging, and finally ending with a death-knell sounding ka-whoosh out the carburetor. I don't see you describing either of those conditions, so it's back to square one. Perhaps the ignition switch down the column is bad. There is a spring inside that pushes the contacts apart when the column key is released and it should do so smartly. If it's dragging it's *ss, then maybe the "run" position contact is getting pushed off it's position and the ignition quits, but then the "start" position contact slowly passes by and is re-energising the ignition for a moment. Both the "start" and "run" positions include "ignition on". Or, I'm over thinking this whole thing and should just shut up.

 

[Faulk21NG238]

Well maybe this helps. Now that you say "dieseling is a pretty intense condition with hammering, clunking, chugging, and finally ending with a death-knell sounding ka-whoosh out the carburetor" it brings back some memory. There was one time when the car sent a puff of smoke out through the carburetor. When it does "start back up" it definitely doesn't sound "smooth". There is a little bit of knock to it. What can I do to fix this? Jshock mentioned that it may have too much fuel. I am pretty much an amateur when it comes to fine tuning things (carb, timing, ignition). My mechanic adjusted all of this.

As mentioned previously, the prior engine never had these problems. The only thing that has changed since it ran 2 years ago are:

1. Converted stock alternator to a one wire alternator

2. Fuel like from 3/8 to 1/2

3. He (mechanic) adjusted the carburetor on it

Don't know if this is a sign, but the engine really doesn't like running while its cold. You have to pump it a few times to get it to fire, then have to feather it for a minute or so for it to run good. If I start it and put it right in gear it wants to die. If I get some heat in it, everything is fine. Once it gets good and hot (180-200) it starts the "dieseling" when the key is shut off. Someone also recommended to rev it up and then shut the key off to see if that changes anything. Any thoughts on this?

 

[woody31]

make sure your electric fans are on a seperate circuit and not on the same one as the primary source for the ignition,,,
ask me how i know,,, 8)

 

[Jshock]

That sounds like a dieseling condition sort of now that you have a bit more detail. Okay so depending on what carb your running changes how to tune it but its all the same concept. First off, idle in park should be around 850 to 900 rpm, should drop to About 600-700 in gear. Change that using the idle speed screw located near the throttle linkage. Then it's the fuel department...the idle mixture screws should be on the front of the carb near the base. (I'd recommend having a timing light with a digital readout but you can do it by ear if you're careful) turn the screw in until you hear about a 50 rpm decrease or the engine starts struggling, at that point turn it back out until the 50 rpm comes back. Then do the other side. Blip the throttle and make sure everything responds well. Then attempt shutting it off and see how that condition works. Also base timing should be roughly 10 to 12 degrees.
PS: MAKE SURE THE CAR IS WARMED UP BEFORE ATTEMPTING ANY OF THIS!
And on a side note, the cold start thing could be the choke improperly adjusted.