1997 Infiniti J30 P0325, P0400, P0443 - Emission Failure After Fuel Pump Replacement

Model: 1997 Infiniti J30 Fault Code: P0325 Posted: 2009-03-16 08:15

My 1997 Infiniti J30 has been failing emissions tests even after clearing the check engine light codes. My stepfather recently replaced the fuel pump using a DIY tool, but now the car is showing persistent fault codes: P0325 (Cylinder 1 Knock Sensor Circuit Malfunction), P0400 (Fuel Pressure Regulator Issue), and P0443 (Evaporative Emission System Vent Control Valve Malfunction). The check engine light has remained on since I purchased the car two years ago. In addition to the codes, I occasionally hear radio interference, which may indicate a wiring short, and the air conditioning does not blow cold air despite having adequate refrigerant—this could point to a faulty AC fan or thermostat issue. A previous mechanic suggested replacing the AC fan as a fix. I'm wondering if these codes are directly related to the fuel pump replacement. How should I diagnose and repair them? Is this repair expensive, and can my stepfather handle it given that he's not a professional mechanic but has extensive car knowledge?