2004 Chevy Trailblazer 4.2 Lt 6 cyl. Service engine soon light is on DTC P0172 Fuel Trim System Rich. Repairs = Serviced transmission, changed fuel filter, air filter and spark plugs.
Question = Symptoms, Engine runs very rough with very little power to go up small hills on highway. Trans was serviced because it was time and while it was in shop I just had it done. After the new plugs were installed it runs not much better. I am stationed in Germany with the military and it is hard to find qualified mechanics to work on American vehicles. I found your web site through yahoo and I am glad you have such a site!!!!!!
Answer: Many things can cause p0172-rich condition. There is a computer re-programming available to correct this code, but not usually a running problem with the engine.
Things that can cause this are excessive high fuel pressure, a stuck open injector (s) caused by contaminated fuel, poor fuel economy, vacuum leaks, a leaking fuel pressure regulator, or just a faulty oxygen sensor.
If running so bad, there should also be a history in the computer for which cylinders are misfiring. A live data stream through a scanner would reveal that. This could give indication as to which cylinder (s) have a problem.
Would suggest having fuel pressure checked, should be about 50psi. Pull the vacuum hose off the fuel pressure regulator to look for signs of fuel in the vacuum hose.