1996 Chevrolet Impala SS 5.7L LT1 with engine codes P0300, P0303, and P0306

Question

My 1996 Impala lt1 Showing PO 300,303, 306 codes. I have changed the distributor cap, rotor, wires, and plugs. Have changed the coil, and fuel pressure regulator, but the car still idles rough in gear. The fuel pressure reads 40 psi with key on and at idle, under driving conditions it reads 41 psi under acceleration, and then when you back off the throttle it reads 38 psi. Is my fuel pump going bad?

Answer 1

HI there,

If the fuel pump were the issue then it would affect all 8 cylinders and not just 2 of them. I would start by checking for intake manifold gasket leaks. If none are found, then the next step would have to be a compression test on the cylinders with the codes. You may have an internal issue causing the misfires.