03 Malibu Crank Position Sensor

Does anyone know that the wave from from a 3100's crank position sensors should look like? I can get a signal from the one on the back by the firewall, but the one behind the balanace I can't get a decent wave form from.

Car is an 03 malibu with a 3100, has 60,000 miles, cranks ok, starts 9 times out of 10, but the once in a while it wont start it either cranks a long time, or it sounds like ignition is out of time. When it does start it runs just fine.

FPR is not leaking, new MAF, No codes. Need advice before Monday. Thats when he's bringing it back.

Check fuel pressure when this happens? Spark? Injector pulse?

When it won't start, spray carb cleaner into the intake, to verify a fuel problem....

Its getting fuel, pressure is at 50psi at idle and when I pull the vacuum line off the fpr it jumps to 60. When it wont start you just flip the key back to off and on, and it cranks and fires right up without issue.

I remember at GM school, they showed a LeSabre with a hard start(only one crank sensor).....showed the leading edge on scope was rounded, instead of a sharp square......because of that round edge, the ICM had trouble reading it....

3.1 has two cramk sensors.....one is used I think for low rpms, and the other for higer rpms......I may be wrong, but I think if one is bad(the low rpm one) it won't start...if the other one goes bad, somehow the ICM will interpolate the higher rpm data from the other crank sensor....maybe someone can expand on this....