2000 OBW Automatic 2.5L 4Cyl. 195K.
It was running fine then started to lose power when accelerating and generally running rough. After running fuel down low and filling up the tank got a P0170 code shortly after that.
Could I have just mucked up some bad fuel at the bottom of the tank which clogged injectors? Any ideas?
The 170 code is a general fuel delivery code that the computer hasn't determined whether its too lean or too rich. It could be either. A number of factors determine the fuel trim. It is a code that sets after the computer sees a problem over a period of time. That period is generally within a single drive cycle or about 20-30 miles of driving. Sometimes, depending on the severity of the fuel trim, quicker.
The AF sensor, the front one, lets the computer know what the fuel trim level is at within the exhaust gases exiting the engine prior to the CAT. The rear O2 sensor lets the computer know if the CAT is actually doing its job as designed or if there is another issue that is effecting the CAT's performance. Since your computer knows the state of the sensors, they are most likely good.
Things to look in to:
Fuel quality Yes, a bad tank of gas will effect the fuel trims if it is not burning properly.
MAP sensor manifold pressure feedback to the ECM
MAF sensor How much air is feeding into the engine
Fuel Filter Flow 'nuf said
Fuel Pump Output Same as above
Fuel pressure regulator Causes back pressure on the fuel rails to allow for a proper spray pattern at the injector to provide for proper atomization and combustion. A dirty spray will cause a rich value from the AF sensor.
Dirty air filter Engine has to breath
Clogged PCV valve Same as above
Vacuum leak Throws off values of MAP and MAF making the engine run lean.
If its been over 15k since you replaced the fuel filter, start there, clear the MIL and drive it.
Use a good quality gasoline. No Murphy station gas. It's no good for the engine.
Tune up???????
