If your 1997 7.3L Powerstroke seems to be losing prime or sucking air, it could potentially be due to a few different reasons. Let's go through some troubleshooting steps to help you determine the root cause.

1. Check for fuel leaks: Start by inspecting the fuel system for any visible signs of leaks. This includes checking the fuel lines, fuel filter, and fittings. Any leakage can introduce air into the system and cause loss of prime. Repair any leaks or loose fittings as necessary.

2. Inspect the fuel filter: A clogged or dirty fuel filter can restrict fuel flow, leading to loss of prime. Remove the fuel filter and inspect it for any signs of dirt, debris, or clogs. If needed, replace the fuel filter with a new one.

3. Check the fuel pump: A faulty fuel pump can also result in loss of prime or air intrusion. Ensure that the fuel pump is operating correctly by checking its pressure and flow rate. Refer to the manufacturer's specifications for the recommended values. If the fuel pump is malfunctioning, it may need to be repaired or replaced.

4. Verify the IPR valve: The Injection Pressure Regulator (IPR) valve regulates the oil pressure in the fuel injection system. A faulty IPR valve can cause issues with fuel delivery, resulting in loss of prime. Use a pressure gauge to measure the oil pressure at the IPR valve. A pressure reading outside the recommended range could indicate a problem with the IPR valve. Consider servicing or replacing it, if required.

5. Inspect fuel lines and connections: Examine the fuel lines, fittings, and connections for any cracks, loose connections, or damage. Even a small air leak can affect the fuel system's prime. Tighten or replace any damaged parts as necessary.

6. Check the fuel tank vent: An obstructed or clogged fuel tank vent can create a vacuum in the fuel system and lead to loss of prime. Ensure that the fuel tank vent is clear of debris and functioning properly. If needed, clean or replace the vent.

If you have completed the above steps and are still experiencing issues with loss of prime or air intrusion in your 1997 7.3L Powerstroke, further diagnosis may be required. Consider seeking assistance from a professional mechanic who specializes in diesel engines. They have the necessary tools and expertise to diagnose and repair complex fuel system issues.