On a 2002 ls1 engine, which sensor triggers the coils to provide spark. The camshaft or the crankshaft sensor

 

Since the LS1 has 8 discrete coils, and the injectors fire sequentially, the spark and the injectors have to be timed off the cam position sensor. But there is a backup, in case the CMP fails.

In effect, the crank position sensor (CKP) tells the PCM which cylinder is approaching top dead center, and the single pulse of the cam position sensor (CMP) tells the PCM if that cylinder is approaching TDC on the compression stroke or the exhaust stroke.

It is possible for the engine to start based only on the CKP, but it's a 50/50 chance whether it will start or not, since the PCM just guesses if the cylinder is on the compression or exhaust stroke, and only guesses right 1/2 of the time. If the engine is cranking, and there is no evidence that it is starting (increasing RPM), the PCM resynchs to the opposite assumed cam position, and the engine will start.