Join Date: Apr 2004
Location: Dodgeville, MI
Vehicle: 2001 Dakota, RC 2x4 3.9L
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An intermittent fault in the cam and crank triggers is hard to catch. They both produce an oscillating signal, so unless the sensor is completely toast and stuck high or low, you need an oscilloscope to figure out if it is throwing junk signal. You also can't diagnose the sensor unless the engine is turning.
I would wait until it starts acting up and refuses to start. While someone cranks it, listen to the ASD relay with a screw driver, or pop the cap and watch it. The relay should click closed when you start cranking and stay closed. If it clicks back open, the PCM is losing crank or cam trigger signal. If it stays closed, then it's something else.
If the relay is clicking open, back probe the crank and cam sensor like you previously did, but hook it up to a test light and watch it while cranking. A good sensor will make the light flash regularly while a bad sensor won't flash or will flash irregularly.