My guess is that the IGBT fails in these devices, most likely a voltage spike from the back EMF from the coil after heat has weakened the electronics.
"The standard points and ignition coil must be retained and the module triggered off that.", said the OP.
The electronics are inside that little plastic encapsulation, I have never busted one open but guessing there is an IGBT inside to do the switching.The Pertronix ignitor (at least the one I ma talking about) is just a Hall effect sensor reading a permanent magnet stuck on the dizzy shaft. No other electronics.
Like this one:
Pertronix 009 Ignitor Kit for VW Beetle, T2 Split and T2 Bay
Quickly and easily installed, our Pertronix 009 Ignitor Kit for VW Beetle, T2 Split and T2 Bay replaces your old worn and unreliable points and condensor with a self contained, maintenance-free electronic ignition unit. Advantages include no points to maintain plus improved engine running and...www.justkampers.com.au
You can see the doodad with the red and black wires coming out of it where the sensor is encapsulated probably in some sort of epoxy.
| Kettering – Magnetic Discharge Ignition (MDI) Contact Points triggered. Energy stored as magnetic energy in the coil. Needs to have a traditional induction primary and secondary coils wound on an iron core. Typically oil filled. Typical turn ratio of 1:80 This system tends to have higher resistance coils to limit the maximum switching current load to around 4-5A on the points. This then self-limits the maximum spark energy output. | Pros Adequate for many decades. Easily fixed. Cons Contact points and rubbing block erosion and wear. Condenser can be faulty. Lose 1/3rd of spark energy in air gap between rotor and distributor cap – this is a function of the rotor/distributor cap and not the MDI. Fixed dwell period: At low RPM, has too much dwell and saturation overheats coil. Runs out of spark energy at higher RPM particularly on 6 & 8 cyl engines. | Improvements Coil secondary windings get hot, and reduce spark energy by 18%. So remote mount the coil to ensure it is cool. Using higher ratio primary to secondary coil windings can provide higher secondary voltages, but will deliver lower spark energy due to the additional resistance in the windings. With limited spark energy, the approach should be to reduce losses. So attention to HT system, eg rotor buttons, caps, HT wires, clean spark plug insulators etc. Condenser is an important component of the MDI, so ensure it has no faults. Twin point distributors can mechanically increase the dwell period, for increased spark energy. |
| Kettering – Magnetic Discharge Ignition (MDI) Inductive or Hall Effect trigger replacement for contact points, Including Solid State switching. Typical products: Pertronix Ignitor Lumenition standard Optronic Magnetronic Gammatronix SherryBerg | Pros. Contact points replaced by a trigger so removes the maintenance of points / condensers. Solid state switching can be more reliable than contact points. | Does not necessarily improve the spark energy from the coil. Same as above. |
| Kettering – Magnetic Discharge Ignition (MDI) Dwell Angle control. This has two approaches. Simple has standard dwell at low RPM, with extended dwell beyond a higher RPM switching point. High Energy Ignition (HEI) The sophisticated approach has closed loop control for coil saturation by modulating the dwell angle. This is achieved by monitoring the frequency of the firing impulse trigger circuit for dwell modulation, and also monitoring and limiting of current flow. These require a low resistance coil. Typical products: 123 Ignition Lumenition Performance Optronic Pertronix Ignitor II Pertronix Ignitor III GM HEI Bosch modules. Bosch BIM024 etc. | Pros. Standard or reduced dwell at lower RPM, with resultant, less heating of coil. Increases dwell at higher RPM, with slightly improved spark energy output with standard coils. Sophisticated versions use low resistance coils to increase maximum current flow, with resultant increased maximum spark energy. Cons Adds complexity | Improvements Some can handle higher primary currents and thus use lower resistance ignition coils for higher spark energy output. The dwell time is monitored and controlled to limit current and consequent heating based on triggering frequency. |
| Capacitor Discharge Ignition (CDI) Energy is stored in the capacitor. Can utilise different triggers. Using a transformer coil (with a continuous iron core) provides 1.63 increased spark energy over traditional induction coil. Typical turn ratio of 1:53 Typical products: MSD 6A M&W Pro 10E Pertronix Second Strike™ Ignition Box | Pros. Coils run cooler. Can provide significantly higher spark energy Cons. Marketing typically refers to the energy stored in the capacitor with high numbers. But usually only 28% of this energy is converted to spark energy at the spark plug via a transformer coil. With standard induction coils the transfer percentage is only 16%. Hence the actual spark energy is similar to a MDI system. Some CDIs only have single polarity discharge eg MSD 6A | CDI can have much shorter spark duration, but higher amperage spark. |
If the flame front does not fill the chamber to create positive pressure at the right time after the intake valve is shut, the vacuum in the cylinder can suck oil up past the piston in the combustion chamber.