Nissan Repair: 2001 Nissan Sentra GXE loss of power, mass air flow sensor, fuel pressure regulator

Question
I have a 2001 Sentra 1.8liter, 63,000 miles, about a week ago the engine started acting up.  It has lost most of it's power and gas mileage has dropped way off.  The car will often hesitate while accelerating and it struggles to get the rpms over 4000.  It doesn't run rough, and the idle is stable. Below about 3500 rpms everything seems normal except underpowered but that part goes in and out. I checked the vacuum lines and there doesn't appear to be any loose wires. Other than that I don't know where to start and don't have much money for a mechanic so I was hoping you may be able to offer some suggestions.  Thank you for your time

Aric

Answer
Aric,

Check the plugs for over richness and you will find which injector is leaking.  That would be my first guess.  The second one is that the fuel pressure regulator is defective in the fuel tank.  Nissan has the pump and regulator in the fuel tank and you have to get a special adapter to check the fuel pressure.  But, the first thing and the easiest one to check is the plugs to see which one is black.  The spark plugs should be gray and if all of them are not the black ones will be the ones where the injectors are leaking.  Change the injector in the cylinder where the plug is black and you should be fine.  If all the plugs are black on the ends then the regulator has failed.  you did not mention if the check engine light was on.  These models have issues with the mass air flow sensor and that can cause over richness too.  But, that is only if the check engine light is on for your particular model and year.