> I got caught with this big time with my programmable ignition,
> until I realised the problem

Same here, and as well as picking up noise from both the ignition
and the electric motor the PIC was controlling, the PIC input was
picking up crap from a 5W radio transmitter a couple of feet away

Circuit was put in a metal box. Wires going in were changed to
grounded / shielded and went in via feed-throughs and had ferrite
beads on them. This substantially reduced noise. Plus the PIC inputs
themselves were protected with RC filters + zeners + Schottkys. No
more false triggering and the real trigger is now quite distinct

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