Scaling a car's injector pulses to count and time them?
That's not real hard, assuming the coil voltage is a rectangular (or even trapezoidal) waveform.







simulate this circuit &ndash; Schematic created using CircuitLab

This will not respond to 30 volt pulses of less than about 100 usec, although it will respond to somewhat shorter 120 volt pulses. R2 keeps the circuit well-behaved if disconnected, and D1 protects against reverse polarity. 

The only possible problem is the relatively slow rise and fall times (about 20 usec), but if this is an issue, add another transistor with an emitter resistor of 5k, and get rise and fall times of 2 or 3 usec. Alternatively, add a Schmitt trigger such as a 74C14 and get rise and fall times of 10 nsec or so.

EDIT - So how do you get 5 nF for C1? Use $$\frac{dv}{dt} = \frac{i}{C} $$
$$ \frac{\Delta v}{\Delta t}=\frac{i}{C}$$
$$C = \frac{i\Delta t}{\Delta v}$$
At low capacitor voltages, all the current through R1 goes to charging C1, and at about 0.65 volts the transistor base-emitter junction will begin to conduct and turn on the transistor. At 30 volts, 1M produces 30 uA, so $$C = \frac{i\Delta t}{\Delta v} = \frac{3 x 10^{-5}\times 10^{-4}}{.7}=4.6x10^{-9} = 5 nF \text{(close enough)}$$