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O2 Sensor aftermarket issues

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Today, I was listening to your podcast #011. You had a discussion regarding the failure of O2 sensors in aftermarket applications. I am currently experiencing this exact issue with a Performance Electronics ECU and two O2 Sensor modules. They are eating O2 sensors. They use a Bosch 4.9 sensor and they seem to be failing within a couple hours of use. They start out OK but seem to fail at some point then drift off to indicating lean condition regardless of fuel or motor tune. At $100 a sensor, this is not a consumable like oil, it is getting a little expensive to play. These are installed in the sidepipe collectors of a Cobra replica, the sensors come in from the side of the pipe but do angle up about 10-15 degrees, within the specified range of Bosch. The injection system is a Borla EightStack ITB's.

I previously ran a similar system that used Daytona Sensor's module with two 4.2 sensors in it. That system performed flawlessly for 30,000 miles.

In the podcast, you mentioned a modification to block the perimeter sensing holes. I am curious to learn more about this. Can you expand on how you blocked those holes and still able to screw in the sensor?

I am also in touch with the manufacturer of the system who is also seeing issues with some installs on some dirt track roundy-round racers. They start out fine but fail within a day of racing. They are seeing a failure rate around 10-15% which is not helping their reputation of quality, performance and endurance.

Any ideas on causation and even more importantly, how to correct?


I would be suspicious of the controller's heater strategy if sensors are failing that quickly in a relatively "gentle" application. What I mean by "gentle application" would be EGT's below 900°C and not heavy exposure to aggressive sustained backfires. Typically failures are caused by thermal fatigue or mechanical shock of the ceramic, if this is not being caused by the engine operating conditions such as those mentioned above then the next suspect in line would be the heater control. You also may need to consider "poisoning" although it is less common nowadays as more people are aware of it - but many silicon-based RTV sealants, silicon-based sprays and lubricants, and leaded fuels can poison the sensor.

In my experience an LSU 4.9 with a good controller that follows the bosch heating practice in this type of application should last several years.

If your controller starts the heater before the engine then you may see some benefit from setting up the ecu so the sensors only start heating shortly after the engine has started so that condensate is not hitting the already hot sensor.

We usually reply within 12hrs (often sooner)

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