[Gmecm] erratic 3.8L Cam sensor alarms

[Ron Drew]

Has anyone experienced problems with a GM 3.8L (1989 with 122K miles) 
missing cam position pulses? More specifically, the pulses generally begin 
to miss when the car has been driven for a while on warmer days; and it only 
seems to trigger the alarm at lower speeds.

This what I have done:
- I replaced the ECM with a known good spare which did not help.
- I've tried a couple of different brands of sensors, which did not help 
(they all behave the same).
- The crank sensor works flawlessly; the cam sensor shares the same '+ 
volts' & 'ground' with the crank sensor, so any problems with the '+ volts' 
and 'ground' would need to exist on a very short run of wiring between the 
Crank and cam position sensors.
- I have not yet scoped the sensor line going back to the ECM.

I suspect the problem may be with the position indicator mounted on the cam 
sprocket. I don't know if this is a permament magnet or a normal piece of 
metal. As far as I can tell there is no magnetism in the position indicator. 
BTW I may go weeks and not see an alarm, so the problem can be very erratic.

I thought I'd check here and see if nayone has experienced this or has any 
ideas.

Thanks
Ron