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O2 sensor issues

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  • O2 sensor issues

    Hi im trying to fix a problem that started as a very rich idle after install on 351W (11) and it was stationary on 11 Corr. 25 !
    After warmup i tried to raise the rpm´s, then it surged a lot but when i hit around 2000/2500 RPM the O2 sensor wakes up and looks to read what´s happening. (probably because of the heat)
    My exhaust is 100% without leaks.
    I took the O2 sensor out to test it. And it doesn't heat up !

    Question: should´nt the O2 sensor have a constant 12V source to have it heated at al times ? I have absolutely no voltage going to the sensor !

    V2.0 : 125
    ECU 2.8
    Serial 1446
    MAP 36005_V2.TAB
    Last edited by NemesisDenmark; 04-05-2019, 05:28 AM.

  • #2
    Those are classic symptoms of an air leak in the exhaust. The orange wire going to the O2 sensor is powered by the main relay. It only has power when the main relay is on. So when the relay clicks on, you should have power at the sensor. The heater ground does not turn on until the ECU see's RPM. It takes approximately 30 seconds after starting the engine for the sensor to heat up and display a value on the tablet.

    A simple test of the sensor is to remove it from the exhaust and plug the hole with an old spark plug. Start the engine and let it run for at least 30 seconds. Then on the tablet you should see around 20:1 AFR, with the engine still running, take a butane lighter and hold it at the tip of the O2 sensor. Depress the button to start the butane flowing, but do not turn the striker wheel to make a spark and flame. While you hold the lighter in place the AFR on the tablet should drop down to 10-11. This indicates the sensor is working normally. If it doesn't change from 20, then the sensor is bad.