Pete, you know more about electronics than I do.

I have a Speeduino, its Arduino based. Uses the Mega2560. Plus a dedicated shield. Its for ignition and fuel injection.

I have no idea how 123 works, however ...

Regarding, your 2 wire cops, you may just be able to add a resistor in series. Again, however! You have 2 coils being (im guessing) supplied from one channel from the 123. So your coils are going to be wired in parallel. If I recall ohms law correctly, the resistance of the coils will be reduced further, I think halved in this case. Look it up. Therefore, the resistor you add in series Would need to compensate for it. It think the rationale behind the correct resistance is to ensure you dont pull to many amps and overload the traces in the 123.

Other useful things to reseach are

Bosch 211
Its basiclly an array of transistors that is specifically designed for switching on Ignition coils. Its 4 channel.

Another wayits to optically isolate the coils, though you still need your required resistance. Again, its a transistor, but this time the coil circuit is completely isolated from the 123 circuit. Its all in one chip, but the switch is operated by light, so the circuits never touch.

You may just need a small resistor in line though.

Pete

Some of the guys on the speeeduino forum use opto isolators to avoid flyback to the ecus. A useful box to put it in, and I believe they utilise the coil inside, is a relay enclosure. Prise it apart, take out what you dont need, add what you do. Use the spade terminals to connect up.

Thanks,.
Have done some searches, but currently busy, bit of welding etc... for an MOT:(

@subarupete

Hey Pete
Did you investigate this any further?

I have kind of the same problem. Two cops placed in series on an ECU, wires to the sensors are screened, wires to the cops are not. A lot of misfires happen, the read out on the computer screen shows as if there is a high reving even at idle. With more open trottle, engine doesn't pick up. I will study this phenomena after I get my car through MOT (maybe tomorrow ?) First thought is to insulate the cops on the lower side by adding a plastic tube around it. If there is still flyback, I need to get the non-screened wires apart. If this does not help, I have to screen all wires etc etc.....

@edce
I may have asked you before. Do you have resistor type spark plugs?

RogerV; I have NGK BP6EF S sparkplugs on a Visa engine. I have checked them, they are without an R so without a resistor. Will change them to NGK BPR6EF.
I always have thought that I used the resistor types of qparkplugs. Thanks RogerV for letting me check again !

I got a new live for two years for my car ! So that's the good news. Hopefully tomorrow I can fix the flyback issue.

That is good news

Second good news is that flyback issue is solved too. Resistor inside plug is the solution. Tnks again RogerV !!!