MSD Street-Fire engine run-on confusion
 

After toasting another Duraspark module on my '76 F150's 460 (even after using the correct ballast resistor with my Accel super-coil) I tossed the resistor and Duraspark for an MSD Street-Fire. Great little unit and I noticed a HUGE difference - the motor runs a lot smoother and definitely has more balls but it randomly keeps running with the key off.

MSD gives you a diode in their instalation bag to solder inline with the #1 terminal (which supplies the "charging lamp indicator") on the voltage regulator that is supposed to remedy this problem. However, the #1 terminal on my voltage regulator is not used - there's not a wire running to it from the harness.

Q.1 - when they say "charging lamp indicator" I take it they're referring to the ALT gauge in the truck?

Q.2 - does anyone know specifically which wire I have to solder the diode inline with under the hood to solve this problem?

I will try calling MSD's tech line tomorrow and see what they have to say but I have the feeling they're going to give me a generic answer that will leave me at Q.2 again.

Thanks for the help!
-Crazy Eddie :-X20

Get ready to sit on hold. It kind of depends as to which wire, does your gauge do Volts or amps? If it's volts, then you want the wire that goes to the gauge. If it's amps, then not so much as amps will be two wires connected to a shunt on the charge wire.

This is going back a ways for me, but there should be three wires on the back of the alt. F L and I think it's C. The Field and the lamp wires should have 12v as soon as you turn the ignition on.

On my 79 150 I put in a 6off road and had no issues. Have you eliminated any other issues? Is the red wire on the box getting 12 after the key is off, say like the switch is acting up? Are you using the correct up on the box (White for points and grn/pur I think for magnetic)? That maybe a work around until you get it solved, if you are using the mag pickup, grounding the white wire will shut down the ignition system.

Thanks for the reply! My ignition switch was questionable so I just replaced it. The box still wouldn't shut down so I did some research on google and someone said to unplug the brown wire on the side of the solenoid (fender apron mounted) and the problem would be solved - someone was right because it hasn't acted up yet :-roll

If you don't mind lending some more info, I want to pick your brain again. The truck's ignition has been randomly dropping off on me also. I thought it might be related to the run-on problem, but apparently not. All of my connections are legit - everything soldered and heat-shrinked, negative and positive connect right at the battery (so faulty ground connection is out of the picture), small red wire spliced into the green/yellow wire from the ignition switch (checked voltage - getting dead nutz 12v), and I'm running the mag. pickup so white wire connector is cut off and heat shrinked. On the distributor/coil end, new cap and rotor, good plug wires, and an older Accel Super Coil.

1. It couldn't be the coil because it ran fine with the Duraspark unit before swapping to the MSD unit (unless the Accel coil doesn't get along good with the MSD box?)

2. I sat and waited for it to quit while it was idling and it started misfiring before it finally took in its last breath. Every time it misfired, the LED on the box quit blinking (seems if the coil was causing a misfire, the LED would keep blinking)

3. Since I mounted the Accel coil on the fender apron I never bought a slightly longer coil wire to reach so I tapped into a new set of spiral-wound plug wires and just used a plug wire. I tried wiggling the coil wire around on both sides to see if I'm getting a bad connection - no misfires, and I didn't get blown out of my socks :-X14 Coil wire can be spiral-wound like a plug wire right?

If I can't get this damn thing figured out, MSD's gonna get a small wooden coffin sent UPS with a StreetFire box inside :-X09

Thanks for your input ReAX. I think maybe after this post I'll write a novel!

-Ed

I don't know so much about the street fire line, but the regular boxes, MSD will make right. You can also go to any shop with the MSD Persuader and have it tested. The Persuader with the coil, also has test connectors on the back just for running an external unit.

Yes, a coil wire can be spiral wound. The spiral winding creates an impedance much like a resistor core wire would, so the longer the wire, the less energy you'll deliver to the dizzy. The winding is also supposed to reduce EMI which is why you don't see anything else these days. In my days of pushing parts, Accel's coils sucked. They were the cheap option for a reason. That said I did run one of the huge Supercoils on my 79 with the 6off road box without problems.

The box should be able to diagnose the problem down for you. If the ignition wire has power, and the trigger wires have an input, then the box will fire. If either of these two inputs fail, then the engine will not have spark. The LED on the box may be showing pickup voltage from the distributor, the dist can produce a small AC voltage (usually 1-5VAC) which could be enough to trigger the LED.

I would start by checking voltages. First the ignition switch input, that it have 0vdc when the ignition is off and the engine is still running. If you still have voltage it's something before the MSD box. If you don't and the engine is running, check for an AC voltage on the coil trigger wire (orange I believe). You shouldn't have voltage on the coil trigger if the MSD is off.

Run on and general misses could just be a compression or heat issue. With a carb motor, anytime the cylinder can be ignited, it will continue running.

I tested voltages on everything ignition related, with the key on/off. Everything as far as the run-on situation seems solved so far.

I did a few hours worth of research tonight and I'm coming across more and more guys having the same issues as me. The intermittent stalls are really pissing me off. Let it sit for a second after it stalls and it fires right up and drives good for 5-minutes then misses a beat or two and stalls again.

It looks like I'll be calling a few performance shops to see if they have the Persuader. In the mean time, I guess I'll hook up the a stock Duraspark coil and see if it sputters out on me tomorrow. If not, the yellow-brick will find its way to the nearest garbage can.

The MSD boxes are pretty stable. I'd try another coil first, coils do fail. It sounds like it could be a heat related impedance issue with the coil to me. Good luck.

Swapped in the Duraspark coil out of my brother's '77 (his truck's running good so I know the coil's good) - it's still up to its same antics. The ignition cuts in and out really quick, like a bad misfire, then off she goes. I also tested the windings of both coils with my multi-meter and both read almost exactly the same. So the coil's off the :-X09 list.

Tomorrow I'm running a line directly from the small red wire to the ignition switch. As of now the small red is soldered onto an OE line from the switch - maybe it's shorted somewhere. It's just funny that it didn't cause any problems before the MSD box.

Isn't there an ignition switch wire on these trucks that have a resistor integrated into the harness somewhere in the dash?

By the time I get done running wire under the hood it's going to end up looking like a bowl of spagetti :-missingt

I don't know that one, but if there was a resistor on the line, you'd see less than battery voltage. The MSD box should run in the 11-16v range. Did you find a MSD Persuader?

No luck on the MSD persuader. There's not a performance shop in my area that has one.

As of now I'm going to see if the MSD techs on MSD's Tech. Forum can give me an idea as to what's going on.

I bypassed the ignition switch all together and ran the small red directly to the battery with a toggle switch at the battery to shut off the box. It quits on me less than it did before, but it still stalls at least once every time I take it out. I even tried a different toggle switch to rule that out and no luck.

WHAT was I thinking when I junked the Duraspark? :-X15

Problem solved. I bought another MSD box, soldered everything together, and the truck runs awesome now. It was the box after all. MSD is sending me another box, (which I will take back to the store to get my money back) and I will send them the faulty unit. MSD's pretty quick with their customer service on the internet!