OK to change I/O pins ?
 

Was there a reason for putting the Injector input on, specifically, Digital 2 & 3? I'm thinking it would make more sense to put them on Dig 15 & 16 (aka Analog 1 & 2), so that all inputs are clustered together, and the top row can be pretty much dedicated to the LCD.

Can anyone foresee any problems with this move, other than me having to mod the source with each rev? Is there an actual, physical difference between the "Digital" and "Analog" input lines?

Aside from that, I'd also like to rearrange a couple LCD wires that criss-cross.

2 and 3 are the external interrupt pins, they are special because they can differentiate between a rising signal and a falling signal. So essentially one pin fires a tiny bit of code when the injector opens and one the other one fires a tiny bit of code when it closes.

This eliminates any guesswork in the interrupt.

The LCD wires were chosen because they were convenient for standard arduino layout and left some multi purpose pins open. Will probably change in the prebuilt code someday.

Thanks for the explanation. Guess i'll just leave well enough alone.

wrt the LCD, were you trying to leave the PWM pins open? That i can understand, but Dig 4,5,6 connect to LCD 4,6,3. D 4,5,6 --> L 3,4,6 looks cleaner ... unless there is another special signalling issue that forced this arrangement.

one of them got crossed when I realized I could control contrast via pwm, that may be what you are seeing.