1996 Dodge Neon emissions test faild

  • 1996 DODGE NEON
Engine Mechanical problem
1996 Dodge Neon 4 cyl Front Wheel Drive Manual

I keep failing smog test its running to rich but the check engine light is coming on, the code PO171. Running to lean. I replaced the upstream oxy sensor but the down stream oxy sensor is not showing any voltage. Today when I drove home from the smog test it was dieing at every stop light but it would start up right of way and ran fine?
Do you
have the same problem?
Wednesday, March 26th, 2008 AT 5:43 PM

1 Reply

Rich codes include P0172 & P0175. Typical symptoms of an engine that is running rich (too much fuel, not enough air) are poor fuel economy, elevated emissions (Carbon monoxide or CO), and engine may have rough idle or surge condition.

Possible causes include a bad O2 sensor, excessive fuel pressure (bad fuel pressure regulator or plugged return line), leaky fuel injectors, dirty air filter or restricted air inlet, or a defective coolant sensor that prevents the engine management system from going into closed loop mode.

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 8 from zero. If STFT and/or LTFT are more than about +10 or higher, it indicates the engine is running LEAN. Negative numbers (-10 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)
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Wednesday, March 26th, 2008 AT 8:20 PM

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