its most likely not your coil. If I had a $1 bill for every coil changed without testing that was actually good, I would be a billionaire

you can test the coil by rapidly applying and removing the ground from the coil (assuming you have full ignition voltage on the coil + )

TEST TEST TEST and TEST prior to ever spending beer tolkens on parts

do you have power to the coil +. is is within 0.1 volts of full battery power? if yes, continue below, if not, find your ignition supply voltage issue.

assuming you have good ignition voltage, disconnect your coil wires and check the coil windings with a DVM. measure the primary side coil resistance. should be about 1.5-3 ohms

if that passes, measure the secondary side of the coil. should be about 6000-15000 ohms.

if that passes, hook power up to the coil +, install your spark gap tester between the coil tower and ground, and then using a jumper wire from the coil negative to ground, rapidly make contact. the coil should spark. if it does, its not the coil. Check your ICM

 

So with regard to testing the coil by pulling off ground, what would I be looking for when pulling it on and off quickly?

 

Thanks for the reply. I’ll give it a whirl and let you know.

 

Just make sure to use a multimeter and check voltage. Not a test light.

 

Unilites need to be grounded very well. They don't like dirty voltage, at all. In fact theres an electrical "filter" you can wire in to protect the Unilite distributor.

 

" I have to give it gas..."

That makes me feel like it's not an ignition / coil issue and rather one relating to fuel.

 

It feels like the idle that was used for the Mallory is not usable for the new coil. Possibly because of resistance?

 

Ok gents,
So I hooked back up my old Mallory Promaster and started right up, idles great. Swapped it, starts right up will idle if i increase the rpm. Not sure if change in these #s matters, but here they are...



Mallory Promaster

• Primary Resistance:
  0.600 ohms
• Maximum Voltage:
  49,000 V
  Turns Ratio:
  94:1
  Secondary Resistance:
  11.30K ohms
  Inductance:
  7.50 mH
  Peak Current:
  66 mA
  Spark Duration:
  3,600 uS

Speedmaster PC-91

• Primary Resistance - 0.450 ohms
• Turns Ratio - 100:1
• Maximum Voltage - 60,000 V

 

Speedmaster PC-91

This ight here could well be your problem, even if brand new.
Speedmaster does not have a spectacular reputation for quality. Or for having honest business practices.
Do a Google search on it, you'll see what i mean.

You'll find more than a few people who will warn you "nothing from SpeedMaster(ProComp) electrical or fuel, as the initial out of the box failure rate and/or short life are high".

 

The lower resistance of the PC91 coil allows more current flow through the module, the switching transistor inside overheats and either temporarily shuts off or may just die. I’d start packing a new module even if this one works.

This is what makes impedance matching of coil to the electronic switching device important. You might say that lowering the impedance (resistance) is a cheap way of getting more output from the coil. There’s nothing wrong with doing that but the switching mechanism has to be sized to handle the higher current flow without turning into charcoal and smoke.

The real issue is not do much getting a hotter spark as it is getting a hot spark at high RPM. Before electronic devices like capacitive discharge boxes like the 6AL the road to high RPM spark strength was dual points and low impedance coils. HEI was kind of a first step in that points are limited to switching 6 to 9 volts into the coil though they switch the ground side. The transistorized HEI allows switching a coil with 12 volts on the positive side so coils got a 3 to 6 volt boost in primary voltage. Then came capacitive discharge to feed the coil and now the primary voltage on the coil can be pumped from 12 to 50 volts. So while we can’t change the build up time because RPM limits that but now we can shock the coil with a lot more voltage making for a stronger magnetic field within the time alloted making for a stronger high RPM spark. CD has spark duration problems at low speeds so we add a timing circuit that shocks the coil multiple times as lower RPMs so the lack of a long duration spark is made up with a fast bunch of sparks. So there’s the Rocket Science history lesson of where distributor ignition is today.

Bogie

 

The PC1 was just installed, and ran for less than 15 seconds. Would you still consider replacement of the ignition module? Could the ignition module be my culprit of turning off after 5 mins? BTW the 5 minute runtime is the reason i went to replace the coil, not because I installed the PC91

 

Ok, I tested the module using instructions on Mallory Unilite. Looks good as far as voltage (12.1) and voltage drop when covering (1.8).

 

ok I see how the title could be confusing, so let me clarify.
1. Before changing anything, the truck would turn off and stall. I’d wait for a few mins, then it would turn back on.
2. research had me believe the coil was the culprit, so I asked for a replacement here. Some advice was the pc coil.
3. Swapped it out, but wouldn’t stay on with new coil without increasing rpm’s. I never ran it for more than 10 to 15 seconds with new coil because I felt something was wrong.
4. swapped old Mallory coil back, everything as was before all this started. Good idle, quick start. I didn’t check after warm up.

 

I’m currently fighting a similar problem with my Frankenmouse, It starts and runs for a few minutes when cold, quits when it gets warm, restarts immediately runs for a few seconds then quits, rinse and repeat as long as you want to play with it. I’m really short on time right now because of wife’s surgery needs but did replace module and coil to no change coil being PC 91 distributor Speedmaster 7000 installed as a test several years ago before I retired never gave problems so the test became the “fix”. Did a propane bleed into the air horn it quit anyway Carb is AVS it has good fuel pressure, pulled the top off when it quit, bowls correctly filled. That leaves the sensor controlling the module switching. But testing that is a few days away till wifey is up and about without constant assistance, hip replacement.

Bogie

 

Godspeed on her recovery sir…

 

Thank you for the kind words. Getting old ain’t for the faint of heart.

Bogie

 

A little update...

After some more research, it looks like problems such as I'm having were common back in the day and the culprit was ballast resistor...common enough that people would carry around extras just in case. Cheap part, easy swap. Ok so now I have the problem of #1 finding one and #2 determining what OHMs i should be using...
I found one at autozone, ran across town to buy it, then it broke in my hands. The ceramic is only on the outside and not filled like the original.

 

Malory makes a good one, although the bracket rusts when used on a boat, Standard Motor Products RU-11 is a good one. available even on Amazon

 

Ok, a little update.... believe it or not, these Ballast Resistors are not easy to find at the parts store. I found a couple at the auto parts store, purchased one, and it cracked in my hands. Returned it and got another one...OHMs are at 3.4
Found a Mallory one and ordered it per Scott (thanks!)...it'll be here next week. ill let you know what happens