I am working on a 1990 chevy p/u, and having the following problem, the check engine light does not come on and the vehicle will crank but does not get fuel from injectors. If I short across the oil pressure sensor the light comes on and truck starts and runs for 20 seconds and then fuel shuts off.

This link should help:

https://www.askmehelpdesk.com/cars-t...ml#post2123675

Be sure to test all under hood and under dash fuses. Also, check/replace the fuel pump relay. If the problem persists, clean the main PCM ground and check out the PCM.

I also had the Ecm retested, I also checked for codes and there were none

Do you hear the fuel pump run, when the ignition switch is turned to ON?

Yes

I would check/change the sensor. If it is sensing heat(falsely), I could see where it would want to shut fuel down.
Verify you have the correct sensor.