Double Check that the (CKP) Crank Sensor Connector is FIRMLY attached to the Sensor (Lower Rear Driver's Side of 4.2L Engine Block adjacent the 5th Crankshaft Journal position in the Block. The Engine will never start with its absence:
Here are the Reasons
WHY:
The (CPS) Camshaft Position Sensor AND the (CKP) Crankshaft Position Sensor
MUST reconcile with each other in order for the PCM to instruct the EFIs to Spray Fuel ...and Time the Ignition Coils to Fire the COP (Coil On Plugs) at their precise positions BTDC (Before Top Dead Center) during Normal Engine Rotation.
High Mileage Engines with either damage to the #5 Crankshaft Thrust Bearing, a loosened Harmonic Balancer Bolt and HB ...or having a Severely Extended Timing Chain Tensioner along with Badly Grooved Timing Chain Guides and Worn Timing Chain can also contribute to having a No Start Condition.
If the "Falling Edge" of the Dark Blue A/C Sine Wave being picked by the (CKP) Crankshaft Position Sensor is even just a Few Degrees Off the "Rising Edge" of the Red (CPS) Camshaft Sensor Hall Effect Square Wave Signal... Then the GM 4.2L Engine Will NOT Start.
Note that the Light Blue Oval in this Image encompasses a
PERFECT Meeting of the (CKP) Signal within the (CPS) Signal shown in this
RARE attached PICO-Scope "Known Good Wave Form" for Automotive Oscilloscopes when used for comparison on all running GMT360 4.2L Engines during 720 Degrees of Engine Rotation:
What is the present Mileage of your SUV?