May I suggest primary voltage and current along with your injector and maybe the IC command. This would provide you will all the information about primary trigger and validate the primary drive as well.
You will want to be certain to use the 20:1 attenuators for the primary voltage and injector. You'll be looking at nearly 400 volts on the primary kick and 80 to 100 on the injector if it is not clipped. Always use the attenuators when you anticipate more than 50v inputs. If you got your kit from Autonerdz, you have an attenuator for each channel.
Dial samples up to the max and put lots of time on the screen. If using PicoScope 5, enable 'save on trigger' to record (this is broken in the latest 5.16.2 release of PicoScope 5 when using a 3000 series)
I suggest using PicoScope 6 for this task. It can maintain a much more robust sample rate at the longer time bases and no need to do a 'save on trigger' since it always is recording the last x number of screens.
High speed streaming mode in PicoScope 6 begins at 200ms/div. At this time base, with samples dialed up, you will sample at 1MHz per channel on each of the four channels with your 3423 scope. You can't do this with PicoScope 5.xx.
Another technique you can use is to repeat trigger on the injector kick. Since you know this signal fails, the scope will then stop recording when the injector is not firing. This can help you capture the event on a single screen.