Press Release Summary = Many vehicles (Mazda RX7s, for example) have a pump that pumps air directly into the header behind the ports or valves during warm up and then switches to pumping air into the cat after the cat is hot enough.
Press Release Body = Many vehicles (Mazda RX7s, for example) have a pump that pumps air directly into the header behind the ports or valves during warm up and then switches to pumping air into the cat after the cat is hot enough. We have seen numerous cases where the switching valve was completely or partially stuck and air entered into the headers even after it should have been switched off. This will of course make the AFR read lean because of the way WBO2 sensors work. Try to disconnect the air pump and then read AFR.
If your air-pump setup is as described, there's a good chance that your exhaust is in reality very rich, but reading lean during the first 10-15 minutes of operation because air is being mixed into the exhaust before the sensor. When the valve switches, the real rich mixture will be suddenly coming through and the sensor errors out. The 1.1 firmware is supposed to show a \'too rich\' error instead of sensor timing. Internally it is the same error condition, but the firmware checks if the last measurement before the error was very rich (< 9.5 AFR), and if so, it shows "Too Rich" instead of a timing error. If the mixture very suddenly gets too rich, like when the air-valve switches, it does not have time to make a rich measurement before it errors out. Typically with an air-pump system while pumping air before the sensor we see readings of 16-22 AFR because of the air, not 14.
In this case, many users suspect they are getting a timing error from sensor overheating. However, it may not be overheating at all, but running outside the measurement range of the sensor. To tune an air-pump-equipped system you HAVE to disconnect the air-pump. Even when it functions correctly, oscillations in the exhaust system can move mixed-in air to the sensor area and cause erroneous readings.
One other related issue: We've seen cases where an aftermarket ECU was used with a NB02 for closed loop control in conjunction with an air-pump system. The aftermarket ECU was not set up to be air-pump aware (few are) and therefore richened the mixture enough to make its NBO2 show stoich with the air mixed in, while the engine itself was of course running extremely rich.
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2025
