How do I properly figure out what could be wrong? And how can I fix it? I have replaced the fuel pump and filter. I have also check all fuel lines and cannot find the problem. The vehicle will start, however is not running properly. It sputters and coughs giving me the impression there is not enough fuel going to the engine.
Check to make sure the fuel pressure is within spec. Check the fuel pressure regulator, check to make sure the pump is getting 12 volts. Since you feel it is fuel related, check that first. If the check engine light is on, have the computer scanned to identify trouble codes. Most parts stores will do it for you for free.