On a '03 E-150 with a 4.2 motor.... i have a "Flat" space about 10" long on the Exaust pipe going between the Cat and the front of the muffler. it looks like its a Factory impression but i am unsure if it is Factory or the Van has bottomed out somewhere along the line? The check engine light has been comming on and it always says codes P1131 - P1152, i have replaced all 4 of the O2 sensors, replaced the intake gaskets, had the Mass air cleaned, the PVC valve is working properly and the engin runs smoothly, just poor gas milage. Now the mechanic says that this exaust pipe needs to be replaced because its restricting the exaust flow and thats my problem... Can anyone tell me if the "Flat" spot is a Factory depression or is this Mechanic just trying to take my $$$$ aagin. Thank you....