bitchinmustang

I have a 1996 mustang gt 4.6L V8 that has this exhausty smell/smog that lurks up my driver side window and i can see it and smell it. If the car is next to a white wall and the sun shines against the "smog" you can see that there is some type of smog that leaking out and coming up from under the car. Has anyone experienced this before? Also, just recently the check engine light came on to tell me codes P1131 and P0171 which means bank 1 O2 sensor is crapped out or a vacuum line is leaking. I want to know if this is all related or separate issues and where to start. If i replace the O2 sensor will the car stop running lean and i wont smell the exhaust coming up anymore?

Rohan

What kind of exhaust system do you have? If you gut or completely do away with cats then you will get an exhaust smell. It will play havoc with O2 sensors too. Are you for sure running lean?


-Rohan

bitchinmustang

the car is running lean according to the codes it puts out but i'm a rookie fix it yourselfer so i don't know all the terminology. What does it actually mean to run lean?

I have the same exhaust as this one, the gas seems to be coming from or around the catalytic converter, is this a common issue? .Shouldn't i also be getting a code to change the O2 sensor on that side if so much exhaust is leaking out.

http://www.miracerros.com/mustang/pipes_V6_V8.gif

cliffyk

The codes indicate that the sensor is reporting the engine is running lean, not that it actually is running lean--judging by what you report it is likely running very rich. When an O² sensor fails it no longer generates any output voltage and no longer "switches" as the AFR varies--this is the P1131 code.

The P0171 code indicates this "perhaps" lean condition. If you click on the link you will see possible causes and diagnostic tips.

An exhaust leak near the sensor will cause it to report a lean condition. This happens because the exhaust flow is not one homogeneous stream, but rather a series of pulses created by each exhaust event. These pulses have a head, body, and tail; each with different characteristic, with their pressure relative to the outside world being the most significant.

• The head is at a pressure higher than ambient, when it passes the "leak" the gas flows out into the world; but the chemical composition of the gas in the pipe remains unchanged;
  
• The body is at or close to ambient pressure. When it passes the leak nothing happens as it and the ambient pressure are nearly the same--the chemical make-up of the gas in the pipe remains unchanged;
  
• The tail is at less than ambient pressure (nearly a complete vacuum), and when it passes by the leak it sucks in ambient air--changing the exhaust gas chemical composition and making it appear "leaner" to the O2 sensor;

This is why the leak makes the PCM believe the mix is lean, a big or close enough leak can cause the sensor response to slow or even appear "stuck".

If this condition exists long enough the rich mixture (the PCM will richen the mix because it thinks it's lean and the leak prevents it from reporting properly) the O² sensor will be damaged by the overly rich mixture.

The sensor can be bench tested using a propane torch and multimeter, however the exhaust leak needs to be fixed or the "lean" condition will continue, and it will just ruin a new sensor...

bitchinmustang

I think you gave me the best explanation and very detailed, except now the code went away, the car stopped leaking so much smog, and the car stopped sputtering like it was. I am planning on fixing the exhaust and o2 sensors.