my gas mpg has been relly bad latley ie betwen 15-16 mpg. this has been going on for about a year. i have no check engine codes on and have tried various forms of driving. second of all has anyone over removed the cat. does the motor still run alright and does the car gain mpg and horse power

 

oh i have done a complete tune up all new filters,new starter,alternator,waterpump,and the rail pressure is about 3 lbs below spec

 

sounds like a bad fuel pump to me if it is 3 below

 

here are a few things to look at:
you put new plugs in? if so what plugs and what are they gaped at?

what type of oil you running? a high mile synthetic blend might help a little

get a new pcv valve

check for vacuum leaks.

 

Also change your o2 sensor on your rear exhaust manifold.

 

New delco plugs and new wires. Standard conventional mobil 5000 oil, new pcv valve and there are no checkengine lights on. Would the rear o2 throw a code if its bad. Wouldent lower fuel pressure give better mpg

 

actually with lower pressure the spray pattern would not mist like is should and cause wasted fuel.