Car wont crank, It only turns over.

It sounds like you're dealing with a frustrating issue with your 1996 Isuzu Rodeo not starting even after replacing the crank sensor. Let's go through some steps to troubleshoot the problem:

Fuel Delivery: Since you mentioned using starter fluid and the engine still won't start, it's worth checking if the fuel system is delivering fuel properly. Ensure that the fuel pump is working and that there's sufficient fuel pressure reaching the engine. You might need to use a fuel pressure gauge to verify this.

Ignition System: Check if the spark plugs are firing correctly. Remove a spark plug, reconnect it to the spark plug wire, and ground the base of the spark plug to the engine block. Have someone crank the engine while you observe for a strong spark. If there's no spark, there could be an issue with the ignition coil, distributor, ignition control module, or related components.

Crankshaft Position Sensor: Although you replaced the crank sensor, there could still be an issue with the sensor itself or its wiring. Make sure the sensor is properly connected and the wiring is not damaged. Also, ensure that the sensor's air gap is correctly set. The sensor's position and air gap are critical for proper ignition timing.

Security System: Some vehicles have an immobilizer system that can prevent the engine from starting if the security system is triggered. Make sure the security system is not activated and that you're using the correct key.

Timing: Double-check that the engine's timing is properly set. If the timing is significantly off, it can prevent the engine from starting.

Compression: You mentioned that the engine has good compression, which is a positive sign. However, make sure that the timing belt or chain is properly installed and hasn't slipped, as this can affect the engine's timing.

Exhaust System: While the missing catalytic converter might not be the main issue, a severely restricted exhaust system could impact engine performance. However, this might not be the primary reason for the no-start condition.

Diagnostic Codes: Check for any stored diagnostic trouble codes (DTCs) using an OBD-II scanner. Even if the Check Engine light is not illuminated, there could be pending or historical codes that provide clues about the issue.

Check for fuel and spark. Make sure nothing is unplugged. See if you have any codes in the PCM.