イグナイターユニット自作 / Original ignititor unit built (alternative to factory CDI)
The solution I alternatively chose was to build my original ignitor unit, by using ignition electrical components originally equipped on Japanese K-cars that are later designed thus certain robustness is expected, drastically inexpensive and easier to find in the second-hand market, assembling them into a box in the same size of 911 factory CDI box.
The idea was to aim the three targets; reliability, availability of replacement, and inexpensiveness.
One of the components I chose was this. An ignition distributor from an early ’90 Mitsubishi Minica, manufactured by Mitsubishi Electric. I procured three units.
Another one here. A closed magnetic ignition coil widely used on K-cars with the size far smaller than Porsche factory ignition coil designed for CDI.
Opened the cap and looked inside. The black ignitor unit in a crescentic shape is what I need. The signal pickup and ignition rotor in a triangular shape could be used when I would be ready to make the whole ignition system simultaneous firing.
I instantly got connected and checked all the stuff function properly.
Connected power and ground lines…
Put ignition coil connected as well…
Turned the distributor shaft and confirmed that the system properly lets the spark plug fires.
I then switched the signal pickup and ignition rotor with those of 911SC. This was really the moment when a Bosch ignition distributor manufactured in late 70s for Porche 911SC and a Mitsubishi ignitor manufactured in early 90s came across. Turned the shaft, and sparked properly.
Put 911SC distributor back to vehicle and wired it with Mitsubishi ignitor. The idea was that the electrical signal picked up inside the 911SC distributor installed on the vehicle goes into the ignitor inside Mitsubishi distributor temporarily placed on a yellow basket, then ignition signal generated by the Mitsubishi ignitor goes into an ignition coil mounted on vehicle (not shown in pic).
Turned the ignition key, the engine successfully started!
The timing stays good with no necessity of re-adjustment.
The ignitor box I built, with the same three attachment points (one top, two bottom) and almost the same size as the Porsche factory CDI box.
Put all the stuff back to the places as they should, put the electrical lines connected with vehicle-side connector, added one line connecting the negative terminal of ignition coil and tachometer signal input with a resister in between… Started the engine!
Checked re-starting. Idling speed stayed steady.
The photo shows how things are like under a punched metal cover. Three crescentic ignitors are placed, but one of them is being in use for the time being. The rest are for future modification for simultaneous firing. I chose modern waterproof connectors for reliability.
I added an orange LED to monitor the power supply status as I thought it would be a great help to investigate the cause when some failure happens.
Connectors for ignition distributor and coil. I selected a waterproof type for distributor.
The wire harness I fabricated.
Upon all are complete, installed and wired, I confirmed that the system work properly.
The original ignitor box I built installed in place and…
The ignition coil in place as well.
All the ignition system replacement is done. I will go with it for the time being.