I recently just put a used motor from a late 80's chevy truck in my 1989 firebird because the original motor threw a rod. we broke the exhaust manifold bolts that hold the exhaust on so im running open right now. i was driving the other day and after about five minutes of driving the ses light comes on and my car starts running like crap. the idles all screwed up and it feels like the engine lacks alot of power. when i grounded the terminals i got codes 43, 44, and 54. to my understanding 43 was a low voltage to the est. 44 was a lean code. and 54 was low voltage to the fuel pump. i pulled off the connector for the fuel pump relay and it looked all mangled and burnt. the fuel pump does prime when the key is on. i read somewhere on here that a lean condition could cause a code 43. but im not sure thats the problem. any ideas? thankss

5.0 tbi
automatic trans