Possible Explanation for Some O2 Sensors and Headers
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Staging Lane
Joined: Oct 2004
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Possible Explanation for Some O2 Sensors and Headers I found the following explanation while researching the problems that I have been having with the front O2 sensors in my Pacesetter headers.
I realize that several people here have mentioned that the sensors being farther away could be the problem, but this explanation appeals to me and it seems to explain some other O2 sensor problems that I have read about.
If it applies to your situation, then great. If you don't like it or don't agree, then post a response. I'm not the author, just a reporter.
Posted: January 26, 2005 2:34 PM
Okay, this is what I have uncovered.
The problem is simple, but a true cure does not exist. What happened is this; the header, having an actual collector and being made of stainless steel rather then cast iron as the stock manifold is conducts heat away from the exhaust gas faster then the stock manifold. Because of this the O2 sensor that is now further then it used to be and in cooler exhaust gas then it used to be does not see a fast enough switch in the Air/Fuel curve. What I mean by that is the Air/Fuel curve is a sign wave going from lean to rich as it should, with A/F=14.7:1 being the middle of the wave.
Sometimes the problem can be solved with a new O2 sensor, a new heating coil may over come the cooler then normal exhaust gasses, but in time as the heating coil wears out the code will come back once again. Seeing as you just put in brand new sensors that step, as redundant as it becomes over time is not even necessary for you.
The only other solution is to have the code programmed out as you would when you have a car tuned/dyno-tuned. The code will not adversely effect your car from what has been seen in similar cases thus far, but its seems like turning the code off in the PCM is the only way around it.
Headers with longer then standard collectors such as LG Motorsports headers have the problem more often then others, but the problem does occasionally occur with other header manufacturers. Simply put, the exhaust gases are not hot enough for the O2 sensor and it is not seeing a fast enough switch from rich to lean due to the lower temperatures.
I know I really did not give you a solution, but I hope this sheds light on the mystery.
Alex
I realize that several people here have mentioned that the sensors being farther away could be the problem, but this explanation appeals to me and it seems to explain some other O2 sensor problems that I have read about.
If it applies to your situation, then great. If you don't like it or don't agree, then post a response. I'm not the author, just a reporter.
Posted: January 26, 2005 2:34 PM
Okay, this is what I have uncovered.
The problem is simple, but a true cure does not exist. What happened is this; the header, having an actual collector and being made of stainless steel rather then cast iron as the stock manifold is conducts heat away from the exhaust gas faster then the stock manifold. Because of this the O2 sensor that is now further then it used to be and in cooler exhaust gas then it used to be does not see a fast enough switch in the Air/Fuel curve. What I mean by that is the Air/Fuel curve is a sign wave going from lean to rich as it should, with A/F=14.7:1 being the middle of the wave.
Sometimes the problem can be solved with a new O2 sensor, a new heating coil may over come the cooler then normal exhaust gasses, but in time as the heating coil wears out the code will come back once again. Seeing as you just put in brand new sensors that step, as redundant as it becomes over time is not even necessary for you.
The only other solution is to have the code programmed out as you would when you have a car tuned/dyno-tuned. The code will not adversely effect your car from what has been seen in similar cases thus far, but its seems like turning the code off in the PCM is the only way around it.
Headers with longer then standard collectors such as LG Motorsports headers have the problem more often then others, but the problem does occasionally occur with other header manufacturers. Simply put, the exhaust gases are not hot enough for the O2 sensor and it is not seeing a fast enough switch from rich to lean due to the lower temperatures.
I know I really did not give you a solution, but I hope this sheds light on the mystery.
Alex
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Joined: Mar 2003
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Thanks for the post kbreck. This is the known reason here for the majority of slow switching O2s. If you are experiencing this still I would recommend wrapping your headers. I have seen it make a night and day difference on a friends car. Unfortunately, I was not so lucky...
