No Oil Pressure!
 

I just put a new oil pan gasket on my car when my tranny was out and i backed the car out of my garage to let it run for a while and i got back in it and It read 0 oil pressure but the car was running fine. Wouldnt the car run like crap or die if it had no oil pressure? I followed the wiring harness under the car and didnt see any plugs that were unplugged. What could it be?? Where is the sending unit for oil pressure??

Sending unit is on the back of the engine. http://shbox.com/1/oil_pressure_sensor.jpg You probably broke it during your repairs.

The sending unit is on the back of the intake. I was told that these can go out very easily. Check to make sure it's plugged in. If it is, then get a mechanical gauge on it and see if it reads any differently.

If there isn't any pressure with the mechanical gauge, then the most likely possibility is that the pickup fell off into the pan somehow. Knock on the bottom of the pan and see if you can hear it bouncing around.

I can't see how you'd break the sending unit just taking the oil pan off, unless you took the whole motor out.

We just ran in to the same problem new trans and now very low oil pressure, someone shed some light on this one for me please???

I also drop in the red if my car runs for a while standing still once warm. I took it to the shop and with it pretty much almost in the red I had 12psi on the oil which apparently Chevy calls for. My sending unit and wire was changed do to a lot of damage but its still doing it. My car runs fine when it is in the red. Sometimes if I back up with a quick press and release on the pedal and its almost in the red it will hit the red and the engine will almost die but jumps back. Really weird but no one has ever had any answers.

Get a manual gauge on it. Check to see if pressure climbs with more RPM. If it does, then it could be your IAC.