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Should oxygen sensors give the same reading

Discussion in 'VR - VS Holden Commodore (1993 - 1997)' started by Scott1990r, Aug 8, 2018.

  1. Scott1990r

    Scott1990r New Member

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    Getting code 46 fuel/air ratio differs from left to right bank
    All ready done Cam sensor and crank sensor, plugs, leads and mass temp volt as it was throwing other codes although I'm not sure it the Vs throws a code for o2 sensors
    I've chucked a multi reader on 02 sensors as the idle it still slightly out and getting a reading of 0.46 on right sensor and 0.69 on left with I'm guessing is putting out more ratio on the one side throwing it out should I replace both sensors or could it be something else
     
  2. BlackVXGTS

    BlackVXGTS Well-Known Member

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    How are you getting code 46 and the description? Code 46 for a V6 PCM is "No Reference Pulses While Cranking".
     
  3. Scott1990r

    Scott1990r New Member

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    Sorry meant code 78 since I unplugged Oxy sensors to get a reading the code hasn't shown up but the code went away obviously when I reset computer doing other sensors but it's back
     
  4. immortality

    immortality Moderator Staff Member

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    VS V6 has a known wiring issue which stuffs up the O2 readings on one bank.

    You can't really just measure the voltage at the O2 sensor unless in open loop mode, when in closed loop mode the PCM swings the fuel from rich to lean to rich so you won't get a constant reading.
     
  5. Scott1990r

    Scott1990r New Member

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    What's open loop mode?
    What am I best doing first in regards to the error code 78 the idle isn't bad but noticeable and doesn't seem enough pressure coming out the exhaust
     
  6. Scott1990r

    Scott1990r New Member

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    Or could it possibly be the eye valve or iac valve causing it
     
  7. BlackVXGTS

    BlackVXGTS Well-Known Member

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    Here you are, all the things you wanted to know (or maybe didn't want to know) about the V6 Fuel Control System. Also DTC78 info:

    DTC 78 V6 PCM - LONG TERM FUEL TRIM (LTFT) DELTA HIGH

    Circuit Description:
    The PCM controls left to right cylinder bank fuel delivery separately based on their respective oxygen sensor signals. If the PCM detects too great a difference between the left to right cylinder bank Long Term Fuel Trim values, it will set DTC 78.
    DTC 78 will set when the left bank Long Term Fuel Trim value differs from the right bank Long Term Fuel Trim by more than 59% for 32 seconds while in closed loop.
    With a current DTC 78 set, the PCM will not illuminate the MIL (Check Powertrain Lamp). DTC 78 will clear when the fault no longer exists and the ignition switch is cycled "OFF" and "ON".

    Diagnostic Aids:
    Lean or faulty injector(s) on one side of the engine.
    Cracked or fouled spark plug(s).
    Exhaust or inlet manifold leak.
    Make sure oxygen sensor leads are not swapped.
     

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    Last edited: Aug 8, 2018
  8. Scott1990r

    Scott1990r New Member

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    Thanks for that info I've only put new leads and plugs in since last week had a look over them and the sensor wiring and all the plugs leads and wiring looks fine
     
  9. Scott1990r

    Scott1990r New Member

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    Had a close inspection on exhaust and manifold and can't hear any leaks but will double check tomorrow
     
  10. Scott1990r

    Scott1990r New Member

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    All sorted thanks for everyone's reply's I checked injectors and we're all fine today changed the tps and iac valve and also put new oxygen sensors in idles better so much more responsive with no hesitation when you put your foot on throttle I did notice the Iac valve stuck in so weather that was the issue not to sure but one of the three things has made a massive difference if not all of them also new belt and tension pulley
     
  11. Mr exhaust

    Mr exhaust New Member

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    Replace both I'm an exhaust fitter and make sure there's no vacum leaks
     
  12. Scott1990r

    Scott1990r New Member

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    Thanks yeah did do both of them didn't get time to check for any leaks last night so will check all that today
     

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