2005 Cadillac STS • 204,000 miles

The car has a brief hesitation and is rough for a few seconds at times while driving at 30-50 mph when you go to accelerate then it picks up and feels ok, it maybe low power feeling too. The CATs were changed at 196K, the plugs changed at 140K, the Fuel pump not been changed yet and from previous experience a I am thinking it could be the problem. While you are in park and tap the gas to about 2k rpm there seams to be a little roughness and the fuel psi drops about 2-3 psi from 57-58 to 55-56 or so. I hooked up a gauge to the fuel rail watched it while driving too. At steady driving fuel psi is 57, when you tap the pedal it drops to 54-55 ish. At full throttle it drops to 45, and at 3/4 throttle to about 50. Do you think this is a weak fuel pump?
February 28, 2013.

One more thing. Already changed the fuel filter.

Mar 1, 2013.
Fuel pressure should be 55-60 psi, anything lower can cause problems. Try scanning for codes see if anything picks up on it. It may be a vacuum leak as well kind of sounds like wak pum but that is an exspensive fix and not be the problem.

Mar 1, 2013.