I have a 1980 280zx and it when I put the key in to on position, the fuel pump turns on and floods the engine with gas, causing the engine to lock in place. Any idea of what might be causing that?

That's not a fuel pump problem it's an injector or cold start valve problem.  One of those is stuck open.  The pump should be able to run continuously without flooding the engine.

Could be the ECU or it could be a short circuit on the injector wiring.

How long have you had it?

I've had it for about a year

I replaced the injectors and the cold start valve. So I'm guessing it probably the computer then?

Edited March 30, 20205 yr by 12meese

Don't guess. Test.  Disconnect all of the injectors and the CSV and see if they still allow fuel through.  Best to do that test with a pressure gauge, or by removing all of them and watching for leaks.

Or disconnect the ECU and see if they leak.

Why did you replace the injectors and CSV?