to get a reading off a crank sensor or phase sensor you will need an ociliscope or a very acurate analogue volt meter that reads nano volts, if you a are getting a spark to start with, then none at all after its started then you have a coil voltage problem, ie the coil is not going to full voltage after cranking as the coil runs at 12.8 volts during crank then 9.9 volts after the car has started, if its not getting the correct voltage it will not create an intense enough spark, bear in mind that being 1 volt out on your coil input voltage means 200 volts diferent on the output voltage, as they are ineffect a step-up transformer.