I'm loving this. Specially depth of your looking. When I asked the guy who'd designed the circuit if I could eliminate the 100R and 33R, he got quite annoyed
So I'm glad both he and you agree!!
(He is an elderly man with terrible lung disease who gets little help from his MDs. He gets very impatient and has good days and bad days - mostly bad).
If I rebuild the electronics layout to be more "finished and robust", it would be with his blessing. I can only say, "Would it be OK to do such and such?" I might lose his goodwill (expensive as it is!) if I tried a change without his approval.
The resistance of the injector I used to know - it's very low indeed. Can't remember right here. But we do need a big charge. We ran at 12V initially and it just doesn't open fast enough.
Separate Q. When I put the current through the solenoid, I get a big field. (Direction matters because the valve is polarised N-S). When I collapse the current, I get a big EMF (??) - anyway, field - which sets up a new current. Is that in the opposite direction to the original? (There's a double negative in the argument which confuses me). The big diode around the injector is there to allow Earth to neutralise such a current. Right?
The injector mechanism is very clever. Everything is tiny. Huge pressures, tiny bleeds. You have to open the valve fast enough to "beat the bleed" then the needle rises incredibly fast and the fuel sprays in likewise. So these <msec currents are reflected in <msec hydraulic response times.
I'll look at what you are saying about the positioning of the output lines. Sounds OK.
One thing I'd like: little plugs a bit like those they used to have on PCs before USB ports. Or just four small 3 or 4 pin plugs and sockets. It would be good just to have to be able to detach floating leads from the circuit board. Oddly, I can't find anything. Any ideas?
Cheers
Malc