Car Cranks but Won't Start: A Practical Diagnostic Order
If the starter spins the engine normally but it will not run, focus on what the engine needs: adequate cranking speed, spark, fuel, injector control, compression, and correct timing.
Start with scan data
Scan for codes even if the check-engine light is not staying on. Watch engine RPM while cranking; no RPM signal can point toward a crank-sensor or related circuit problem.
Check spark
Use a proper spark tester. No spark across all cylinders sends the diagnosis in a different direction than one dead cylinder.
Check fuel and injector command
Verify fuel pressure to the vehicle's specification and determine whether the injectors are being commanded. Hearing a pump run is not proof of correct pressure.
Do not forget mechanical timing
If spark and fuel are present, compression and valve timing matter. Unusual cranking speed or sound is a reason to check compression and timing.
Bottom line
Diagnose the cause before ordering parts. Vehicle configurations vary, so verify specifications and procedures for your exact year, engine, and model.