91 z24 3.1 randomly will not start

I have a 91 Cavalier z24 that recently has a problem firing up on start. I would turn the key and you would hear the first fire cylinder fire and then I would let off key to expect the car to continue running. It does not. I turn the key again and the engine just turns. Will not fire.

I thought I was dead at work. Waited a bit and thought I would try again (before calling for a tow) and it fire right up and was able to drive home just fine, car performs as it always had.

Tried starting the car this morning and the car will not start again. Just turns over, no spark, or sputter.

I do hear a familiar hum sound when I do turn the key on, prior to putting the key all the way to the start position. So sounds as if fuel pump is working.

Fuel filter was replaced about 9 months ago. So was the wire and plugs.

As stated, once it did start, the one time, it ran as it always has... Just have to figure out why it does not want to fire up at times.

Any help would be appreciated.

After lots of research on the website http://www.v6z24.com/ i was able to narrow down my problem with the CrankShaft Position Sensor. Replaced it and car has start every time :-)