Stumped by random start/no-start runs/dies

[HB73]

Does the msd high vibration coil need a resistor? Electronic ignition, no points.

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[HB73]

Never mind, looks like it's 9 volts at the coil, so I guess the resistor is built in? Or in the controller box?

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[DirtDonk]

On Broncos it was a special wire from the key to the coil. The resistor wire is a smaller gauge, longer run of heavy jacketed and heat protected (to protect the other wires around it when it gets hot, doing it's thing) under the dash.
So your 9v is perfect in my opinion.

The high-vibration coils if they're the epoxy filled type don't usually "need" to use the resistor, but it sometimes depends on what trigger mechanism is used too. In other words if you were using it with points to trigger the spark, you'd still want the resistor.
Pretty sure it won't hurt the coil to run lower voltage, but probably won't hurt it to run full 12v someday either.

What's the part number of the coil? Did it give an internal resistance value with it?

Paul

 

[Jason72Bronco]

Second the thought about boat guys, as I am one of those. My correct craft Ski Nautique would be running great, then just die for no reason. New distributor, plug wires, plugs, nothing helped. It would always die while we were out,and needed to be towed in. Well, after checking every ground, and everything else, come to find out it was my wire from the tach grounding in the dash plug. I undid the tach wire from the coil, and presto, runs great. I just bypassed the plug with a new wire. All is good. I would rather the rods be hanging out the side of the block than deal with this kind of stuff. At least I’ll know what’s wrong.

Mike, I would second that checking the tach connection and wiring since it does go to the (-) terminal of the coil, and any irregularities could cause this frustrating problem. As, I mentioned in post #5, I really, really thought that was my problem when I found the wiring job to my tach by the PO was so bad. But after I removed it all, I still had the problem. (However, I wonder if the bad tach wiring job actually may have contributed to the distributor sensor failure...it was a really bad job, and again was connected in with the very important coil terminals.)

 

[Jason72Bronco]

Kind'a makes your brain hurt sometimes, eh? I know it does mine!
In theory it's possible to do what you ask, but you'd want to know the total resistance, which I think is just adding the two values together. As opposed to doing some tricky-math. But I could be wrong.

But if your wire is even remotely near what it used to be, a new regular ballast resistor would probably be too much additional resistance. Bringing your voltage much farther down than would be called for.
I think 'bowsher or Viperwolf or Steve83 (as well as many others) will know what to do in this case.
It might come down to you replacing the resistor wire with a regular wire before running it through a ballast resistor.

Do you have a link to the current Mallory instructions? I always found them very vague (to me at least) on whether the Unilite with a particular coil needed a resistor or not. I used to think it depended on the coil used, and the Unilite could handle the higher voltage at that point. But years of Unilite failures have left me doubting.

Paul

Paul,
Thanks for the response. The part #'s of my ignition setup are in post #5.
I am using the factory resistance wire (the one described by you), and it seems to be working based on my readings. It has always been used as the only mode of resistance.

But Mallory goes over the top in warning about the Unilite module failure if the resistance is not up to snuff, and other users seem to have had this problem.

The only reason I went with the Mallory setup is that it is what was on the truck before, and it just seemed more "period correct." However, the more I research it looks like MSD is just barely keeping the Mallory brand alive.

Anyone with suggestions or reviews on a new electronic distributor for our 302's, I'm open. (I'm not sure how easily they will replace my 6 month old failed unit...and I'm not sure I want it.)
Jason

 

[surfer-b]

Anyone with suggestions or reviews on a new electronic distributor for our 302's, I'm open. (I'm not sure how easily they will replace my 6 month old failed unit...and I'm not sure I want it.)
Jason

I have got to where I look in junkyards for OEM Ford Duraspark Ignition systems, these seem to do better than any I have tried. Also here is the reason I replace the resistor wire, these rigs are old and time has taken its toll on the factory resistor wire, I replace it with standard automotive wire and use an external ballast. This is the resistor wire on a low mileage 77 I replaced

 

[Skytrooper15]

I'm with you on the duraspark 2 ignition Dirtdonk I had one for 30 years and only problem I had was the pickup coil in the distributor went bad.I also used one in a 1973 Bronco I added with no problems at all.Presently I am using the tried and proven original points,condenser and coil and I don't mind setting points every 6,000 miles or longer it takes about 10 minutes.

 

[DirtDonk]

I hear you on points. Kept mine for a long time, but when I started having to actually replace them every 6,000 miles, instead of just cleaning and fine-tuning, I gave up and replaced it with Dura-Spark.

My Red w/green wire read 12v all the time, even after an extended drive, so I figure it had somehow decided to stop resisting and pass full current (the opposite of the usual failure mode) and was just burning things up.
Then of course I had the usual failures of the brand new modules I bought from the local parts stores. Which I also equated to feeding the coil 12v, but not sure if that was the cause or just cheap parts.
Then when I used the Motorsport/MSD modules I never had an issue after that.

Paul

 

[sprdv1]

Kind'a makes your brain hurt sometimes, eh? I know it does mine!
In theory it's possible to do what you ask, but you'd want to know the total resistance, which I think is just adding the two values together. As opposed to doing some tricky-math. But I could be wrong.

Not hard to do w/all the issues..

 

[sprdv1]

I'm with you on the duraspark 2 ignition Dirtdonk I had one for 30 years and only problem I had was the pickup coil in the distributor went bad.I also used one in a 1973 Bronco I added with no problems at all.Presently I am using the tried and proven original points,condenser and coil and I don't mind setting points every 6,000 miles or longer it takes about 10 minutes.

Got to go with what works right...

 

[blubuckaroo]

I'm with you on the duraspark 2 ignition Dirtdonk I had one for 30 years and only problem I had was the pickup coil in the distributor went bad.I also used one in a 1973 Bronco I added with no problems at all.Presently I am using the tried and proven original points,condenser and coil and I don't mind setting points every 6,000 miles or longer it takes about 10 minutes.

I'm with you.
Certainly electronic ignition is basically maintenance free, and has a higher firing voltage. But if your system is kept in shape, and the dwell is correctly set, it works great.
Exactly why I still have a dwell meter in the shop.