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Thread: Tuner ProRT up and running O2 reads

  1. #1
    Electronic Ignition!
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    Sep 2016
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    Tuner ProRT up and running O2 reads

    Are the O2 sensor readings supposed to swing from lean to rich?
    AKWA 1228747
    New Bosh O2 sensor

  2. #2
    Fuel Injected!
    Join Date
    Oct 2013
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    893
    Yes, that is how it works. Pretty much every closed loop system has a slight oscillation around the setpoint. The O2 signal varies rapidly when transitioning between rich and lean so the change in voltage as the oscillation occurs is very obvious. If you watched the AFR with a wideband you'd only see a small oscillation around the setpoint.

  3. #3
    Electronic Ignition!
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    Sep 2016
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    I would think that a slight oscillation would be acceptable. What I see after closed loop is a big swing from say 100 to 800mv and the iac count is 0 at idle. It leads me to believe that there is a vacuum leak at the bottom of the intake manifold which is the only thing I haven't checked. I squirted carb cleaner around the top of the manifold edges and there was no change. The old sbc's when they would leak it would be able to detect this as they had a cast iron intake and when the gaskets wore out they would leak at the top also.
    I would hate to have to pull the intake just to find out it was something else.

  4. #4
    Fuel Injected!
    Join Date
    Oct 2013
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    893
    You're not understanding the O2 sensor response. All a narrowband O2 can do is tell you if the engine is lean = <0.45V or rich = > 0.45V. Google image "O2 sensor response curve". A very small change in the AFR between rich and lean causes a large change in the output voltage. So, as the control loop oscillates slightly around stoichiometric the O2 sensor output voltage swings widely. It happens the same way with every GM using narrow band oxygen sensors, it just happens faster on newer stuff.

    The IAC count at 0 either does indicate a vacuum leak or you need to open the throttle blades slightly. It has nothing to do with the O2 sensor.

  5. #5
    Electronic Ignition!
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    Sep 2016
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    Thanks. I think I've got it now. Can you recommend any good books? I am having trouble learning this stuff on the internet.

  6. #6
    Fuel Injected!
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    Oct 2013
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    893
    I don't know of any books for the old OBDI stuff offhand.

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