Aftermarket ignition problems

[Broncojunkie]

I recently went through an issue with the charging system. I lost an alternator mounting bolt, which was a quick, easy fix. After that, I kept having charging issues. I replaced the battery and eventually the alternator, only to find that the exciter (sensor? trigger?) wire had become damaged down inside the insulation. I finally got that fixed, and the charging system is great again.

So why am I even talking about the charging system? This is a post about aftermarket ignition, right? Well, it's because ever since I've gone through this (off and on for the last couple months), I've had a misfire. Plugs, wires, fuel all perfect.

The car is a 302 with Holley (pro-form) carb, MSD distributor, MSD Blaster 3 coil, and Pertronix HP Digital ignition box. I inspected the distributor and don't see any issues. Checked all wiring connections and grounds with a meter. Ohmed each plug and wire. Checked cylinder temps (to rule out issue with a single cylinder). I suspected the coil or ignition box, so I started by checking voltage going to the coil with ignition on. It was zero. Ifigured maybe the Pertronix box only sends power to the coil under cranking and run, so I checked cranking and it was very low...maybe 3v? I removed the primary wires from the coil and tested again with the same results. So I replaced the wires.

This time, I decided to provide a straight 12v to the coil and see if idle would improve. This setup does not require a ballast resistor, so coil should be receiving 12v. When I hooked up the test lead, it started smoking. After yanking that off, I tested the coil for ground and yep. Straight ground. I swapped in a spare blaster coil I have and it was the same way. I figured something may have failed inside the ignition box, so I opened it up and inspected it. Nothing burned or corroded. Board looks great. No water intrusion. The box also has a self diagnostic test that runs when powered up, but it doesn't flash any codes.

Sorry for the long post, but I wanted to explain how I got to this point. As of now, I have no spark. I do have another ignition box identical to this one, but they're not exactly cheap and I want to make sure I'm covering all bases before swapping it in.

Was I wrong to send power straight to the coil for testing? I know I've done that with other ignition setups, including MSD 6AL. This Pertronix box wires in the same way. I just like it better because it's half the size and has more built-in features. Is there anything besides the ignition box, distributor, or wiring that could cause the coil to ground through the primary winding? I may end up switching to a Duraspark setup, but it seems like they all have their pros & cons.

[gr79]

Post length is ok to me but i post long too. The detailed short story.
Friend did not bring his 71 Mustang Boss 351 to this weekend's cruise because of ignition glitches.
Has Pertronix too. Says is going back to oem dist. Hates setting point dwell but wants to drive it more.
Will post any resolution.

[at_the_junkyard]

Details are always good and usually necessary when trying to solve problems.

I have the same Pertronix digital programmable box I think (510?) and it has worked very well with my Pro flo 4 EFI. However I also bought the recommended matching low resistance Flamethrower coil and it turned out to be intermittent and left me completely stranded once. It took a little while to eliminate all the possibilities but was the coil in the end.

No issues with the replacement coil they sent me. Now I carry a spare MSD coil and setup some quick connectors that I can bypass my ignition box entirely if necessary. Didn't like being helpless lol

During the troubleshooting phase I did change the power output on the Pertronix box from high to low, as I thought maybe this was contributing to the problem (heating?). Never did change it back to high power. Looking back I don't think it had anything to do with my problems. It hasn't missed a beat ever since so I'm not going to mess with it now. Most likely high power is overkill for my car anyway.

Ignition problems can be a real pain to troubleshoot especially intermittent ones. Not sure if that helps.

Cheers

[at_the_junkyard]

Forgot to add that no I don't think the coil should show any connection to ground on the primary.

It should be very low resistance like 1-2 ohms across the terminals. Funny thing is that both your coils are showing this ? Only way I could see this is if its shorting internal to the case and the metal coil clamp is fastened to the chassis ?

[Broncojunkie]

It doesn't show a ground unless either of the two primary wires are attached. But that got me thinking. So I made sure the distributor was completely disconnected (both the pickup connector and the high tension plug wire from the top of the coil). I then unplugged the harness from the ignition box and ohmed the primary coil wires, just to rule out a short somewhere in my wiring job (which I admit is ugly, but solid). Test showed open circuit, so I'm good there. I then plugged the harness back in to the ignition box and repeated the test. This time, I'm showing a dead short. So my coil does seem to be shorting out somewhere in side the Pertronix box.

I dug out my spare Pertronix box, and yes, the model is 510. I plugged it in and repeated the ohm test. This time, it read steady 9.98 resistance. So I'm chalking it up to a failed box that may or may not have been my fault.

Regardless, I believe I'm going to be switching back to the Duraspark system. It may not be any more reliable, due to the current state of manufacturing, but the replacement parts are less expensive and still available at parts stores.

Another issue I noticed is the poor quality of my overpriced MSD distributor. After reading numerous examples and seeing the poor quality first hand, I won't be spending another dime on that stuff.

[at_the_junkyard]

Yes I find the old Ford distributors are not that bad with the magnetic pickup (which MSD apparently copied lol).

I had an original Duraspark ignition module go intermittently bad on my sons car which wasn't the greatest since he drove it daily. Would quit randomly but then again it was 40yrs old etc. It happens apparently with those too.

Another fairly inexpensive upgrade that you might look into is using an HEI module (GM) and wire directly to your mag pickup on the stock Ford distributor. I did this upgrade on my sons car. Gutted out the old electronics and epoxy from the bad duraspark box and mounted the HEI module inside using the metal box as a heatsink and mounting point etc. It has not give any problems and he still drives it regular almost daily etc. Lots of literature online for this upgrade if you search.

[Broncojunkie]

Yes I find the old Ford distributors are not that bad with the magnetic pickup (which MSD apparently copied lol).

I had an original Duraspark ignition module go intermittently bad on my sons car which wasn't the greatest since he drove it daily. Would quit randomly but then again it was 40yrs old etc. It happens apparently with those too.

Another fairly inexpensive upgrade that you might look into is using an HEI module (GM) and wire directly to your mag pickup on the stock Ford distributor. I did this upgrade on my sons car. Gutted out the old electronics and epoxy from the bad duraspark box and mounted the HEI module inside using the metal box as a heatsink and mounting point etc. It has not give any problems and he still drives it regular almost daily etc. Lots of literature online for this upgrade if you search.

This has been on my radar for quite some time, actually. It seems to me I shied away from the HEI setup because it has a lower max rpm and I didn't want it to be a limiting factor in case it ever sees some track time. I may be wrong, though. It's been a while since I've looked into it. I will assure you that it doesn't bother me that it crosses "enemy lines". This car also sports an HHR electric fan lol!

[richpet]

I put a Summit brand HEI dizzy in my Granada. I *think it's rated to 7000 rpm?
Anyway, it has run flawlessly for 2 1/2 years and close to 11000 miles.
I have probably only revved it to about 5k, but no missing or drop off that I could hear or feel.

Sent from my Pixel 6 Pro using Tapatalk

[Broncojunkie]

I put a Summit brand HEI dizzy in my Granada. I *think it's rated to 7000 rpm?
Anyway, it has run flawlessly for 2 1/2 years and close to 11000 miles.
I have probably only revved it to about 5k, but no missing or drop off that I could hear or feel.

Sent from my Pixel 6 Pro using Tapatalk

Interesting. I'll have to start reading up on this stuff again.

[mcfairmont]

I have been running factory Duraspark distributors, both with factory Duraspark ignition modules on my daily drivers, a street/strip cars, and with MSD boxes on my drag cars, and in over 30 years, I have never had a OE FACTORY Duraspark component fail. I never use a parts store aftermarket distributor or module, always grabbed factory install Motorcraft distributors and blue stain Duraspark boxes whenever I found them still in vehicles at the wrecking yards. I have owned 6 78-80 Fairmonts and Zephyrs, with factory Durasparks, and have converted a number of my older Fords from points to Durasparks over the years, and al have been `00% reliable. I would rather run points than one of those huge, ugly Chinese GM HEI distributors, based mainly on the look of them, and they usually require a smaller air cleaner to clear the huge cap. Back in the late 70s-mid 80s, as a mechanic, I changed so many burnt out HEI distributor caps and rotors, failed coils and ignition modules, rusty/seized up advance mechanisms, I wouldn`t even run a HEI on a GM engine. A look under the hood of all the Chevys at a local dragstrip wil show that even the vast majority of Chevy owners won`t run the HEI. Most have MSD distributors, which interestingly, use the Duraspark magnetic pickup design. For most older Fords, with a points ignition system, considering most are nice weather weekend toys, that se limited mileage each year, a decent set of points would likely last quite a few years before replacement or even adjustments are needed. Seems that many people tend to forget that all the older vehicles used points and condensers until the mid 70s, and even back then, people were driving these things to work every day, on across the country vacations, business trips, etc, and were not constantly breaking down, or having to fiddle with their ignition systems on a regular basis.