Secondary ignition image question (with pic)

[Albert850i]

Hi, I used an old scope to show the secondary ignition pattern of both banks of my M70 engine.
The image for bank 1-6 seems to be perfectly OK (perhaps mixture too lean?).
The image for bank 7-12 shows an anomaly during charging of the coil: a flat line.
Anyone a suggestion of what could be going wrong at coil 7-12?
I will continue measurements, also of primary currents at the coils.
sec_ignition_patterns.jpg

[Timm]

I would check the primary and secondary coil resistance - the flat bit before ignition should show current increasing to the point of saturation - and I can't see that. It could also be a measurement error depending on how you have coupled the 'scope probe.

[CD05001CIA]

So trace 1-6 has field building in coil. In 7-12 beautiful digital waveform before spike. I wish all my digital ckts looked that good. Objective of digital ckts -> nil capacitance, nil reluctance. Look for corroded electrical terminals that are limiting current keeping coil from building field.

[Albert850i]

So trace 1-6 has field building in coil. In 7-12 beautiful digital waveform before spike. I wish all my digital ckts looked that good. Objective of digital ckts -> nil capacitance, nil reluctance. Look for corroded electrical terminals that are limiting current keeping coil from building field.

Thanks. Trace 1-6 looks like the reference image in the workshop manual, trace 7-12 does not. In fact trace 7-12 looks like a primary instead of secondary image, but it is really secondary like trace 1-6. The inflow current may be limited, but the field does actually build up in the 7-12 coil.

- - - Updated - - -

I would check the primary and secondary coil resistance - the flat bit before ignition should show current increasing to the point of saturation - and I can't see that. It could also be a measurement error depending on how you have coupled the 'scope probe.

Thanks. Both coils measure 0.5 ohm primary resistance, which seems to be OK. Still the 7-12 current inflow may be limited because of a wiring problem; I will try to measure currents on another scope.
BTW I used an old Bosch MOT-206 scope, and just relocated the pick-up clamp from coil output 1-6 to 7-12. So both graphs are directly comparable.

[Albert850i]

The current inflows of both coils follow a straight line, see image. No horizontal part due to current limiting. I guess that's OK (although most examples show a flat current limiting part).
bobine_primair_stroom_7-12.jpeg
What I noticed is that the secondary traces taken between the coils and distributors look fine (see pic). However, when measured at the individual plugs, many traces are worse causing a lot of misfiring.
Distributor/rotor problem?
plug_1.jpg

[Timm]

That means you have distributor problems - dodgy rotor arm, dirty contacts etc