2001 Ford Ranger, 4.0L V6 engine, 68,000 miles - Check engine light went on and the store said it was Fuel too lean - mixture bank 1 & 2. When you start the car it hesitates and sounds like it is going up and down like to fuel is not getting there. Once it runs for a few minutes it runs fine, but begins again when you start the vehilce. I replaced the fuel filter, still happens.
Read the topic above about the code issues with the 4.0L engine. Carundell has a very good post on the matter
March, 5, 2007 AT 4:22 PM
A code P0171 or P0174 indicate the engine is running lean. This means there is too much air and/or not enough fuel. You can confirm the engine is running lean by looking at Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT). Normally, STFT and LTFT should be plus or minus 5 to 10 from zero. If STFT and/or LTFT are more than about +12, it indicates the engine is running lean. Negative numbers (-12 or more) indicates the engine is running rich.
A lean fuel condition can be caused by: * Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (Use a fuel pressure gauge to check fuel pressure at idle)
* Dirty fuel injectors. (Try cleaning the injectors)
* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)
* Leaky EGR valve. (Check operation of EGR valve)
* Leaky PCV Valve or hose. (Check valve and hose connections)
* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)