Originally Posted by AzEKnightz
Have you personally tried using a gas analyzer and see the result when there is an exhaust leak? What happens to O2 readings?
I can tell you that IT does get through and IT WILL affect O2 reading.
I am not trying to be defensive here, but personally from experience with my exhaust manifold gasket all rusted due to age and heat etc, there was an exhaust leak.
I was lucky enough that I was doing smog class at the time and I was able to put on the smog machine to measure exactly what those readings were about 2 years ago.
Before fix, I had about 2% air leaking through the exhaust gasket. After the replacement of my exhaust manifold gasket (before O2) and I was curious as to the differences of the gasket would make.
So, I decided to put it on the machine and have it analyze the readings again.
Result came out just as expected. O2 reading down to 0.1% and the car was combusting all gas and less HC was measured at the pipe and CO2 level (the quality of a combustion went from about 13.4% - about 14.2%.
Hopefully this help supported my statement
"Exhaust leak infront of O2 = more air into the exhaust and will affect O2 reading. (Extra O2) ECU would compensate for that extra air in the system which will result in extra fuel added to the combustion chamber. "
I admit I'm nitpicking to begin with, but this subject could be important in certain situations.
Here's my problem with it. I don't think air is getting into the exhaust. In order for this to happen, the pressure in the exhaust would have to be lower than the outside. Not the case as far as i know.
Your o2 readings were high. You believe it's because air was getting into the system.
Oxygen is a component of the exhaust gases. I believe that because less exhaust gas was getting to the sensor, the sensor saw less oxygen. Then, to correct the low oxygen reading (a simulated rich condition), the computer leans out the mixture, therefore more oxygen exists after combustion, creating high o2 readings on your analyzer.
Fixing the problem allowed all of the exhaust gasses to reach the sensor, therefore all of the oxygen existing after combustion was registered by the computer. The computer no longer leaned out the mixture because of this.
The system operates on the assumption that all of the gas exiting the engine reaches the o2 sensor because there is no mechanism to measure exhaust gas mass flow rate.
Now, I may be wrong, but this is my understanding of how it works.
Originally Posted by unvmyrx7
another way to find a exhaust leak is to use a shop vacuum in reverse (blower side). place the hose in the exhaust tip, seal it up with duct tape. get a bottle of soapy water, i prefer a few drops of dawn
dishwashing soap. start spraying all the flanges and watch for bubbles.
that's a pretty good idea!