[winker]

The theory was all very well, but here is the real world. The two attachments show that no dangerous spikes are getting through, but the 100k is clipping at 3.8V! The 1k is clipping at 5.04V, which is good enough to backup the theory.

So the fact is that 100k/Zener is protecting against the high spikes, but it appears to be clipping at a lower voltage.

More interestingly is the initial turn on voltage to the injector is negative, and the hold portion is at 0V! I used the negative terminal on the battery as the refernce.