[malc9141]

Thanks, Guys,

First, this collective thinking is useful. So thanks again.

With a diesel there is no distributor.
It fires each 360 rev, so at 2000 rpm it's firing 33 times a second.

The pulse duration is going to be very short but that's what modern injectors do. The duration might be about 10 degrees total (suspect less) so for each 1/33 seconds (= 30 microsecs), the pulse will last 30*10/360, ie 0.8 ms.

That seems very brief (!)
but let's think what an injector is doing in a 4 stroke four cylinder car at 3000 rpm - motorway cruise.

Each cylinder is firing once, each two revs, ie 1500 times per min or 25 times per sec. So we can see it isn't going to be much different from 33 times per sec. Each rev takes 40 ms.
If we stick to a 10 degree dwell for the injection (pure guess), each pulse is 40*10/360, ie 1.1 ms.

Now at idle in the 4 stroke buzz-bomb, the rev time is longer and the pulse duration shorter, but that does imply the solenoids can open/shut this fast.

Next, I'm out of phase with you guys!!! You suggest something, I think, No, won't do. Then you reconsider, and meanwhile, I'm coming round to your earlier way of thinking!
So, what about this? ---->>>

The engine has a 16" dia flywheel (very thick but that's another matter). It has convenient mounting points nearby. The circumference allows exactness.

If I built a small structure that bolted onto the crankcase and had an adjustable extension to contact the flywheel face, we could get a pulse off the f/w by adding the other part of the contact (say a piece of silver) to the f/w. If the silver was roughly triangular, by moving the contact back-forward for advance-retard or up-down for dwell, we might have a useful circuit.

But I don't know if the charge would build fast enough to move the inj solenoid. It would probably need a condenser (discharging) to help it. But it might work, ie going analogue when I assumed (out-of-my-depth) digital.

Comments welcome.

It's all at a planning stage at present.

Malc