Oxygen sensor question

Discussion in 'The Projects Forum' started by royco, Oct 29, 2008.

  1. royco

    Thread Starter New Member

    Oct 28, 2008
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    SgtWookie,

    Thanks for all your input. Very helpful!. I have some questions though. You mentioned that the ECU looks at the passes at 450mv, so what makes it see a lean or a rich mixture? The frequency of passes?

    My car already has a Wideband O2 5 wire ( 2001 VW Passat) , what kind of circuit would it need to modify the AF ratio as seen by the ECU. The main signal wire has like 3V steady.

    Thanks
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    I have moved this new post from this thread - http://forum.allaboutcircuits.com/showthread.php?t=14794&page=8 - which was already hard to follow.

    Welcome to AAC. We encourage posters to always start new threads rather than starting off in a different vein from an existing thread.

    Could you expand on what you mean by "passes"?
     
    Last edited: Oct 29, 2008
  3. royco

    Thread Starter New Member

    Oct 28, 2008
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    Sgt Wonkie mentioned in the original thread I posted in that the ECU looks for crosses on the 450mv threshold. I was wondering what is it actually looking for to see a rich or lean condition. Is it the frequency of crossings over the 450mv or the value thats over or below the 450mv threshold?

    Thanks
     
    Last edited: Oct 29, 2008
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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  5. SgtWookie

    Expert

    Jul 17, 2007
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    Broadband O2 sensors have a relatively linear response from very rich to very lean conditions.

    Narrowband O2 sensors only have a very narrow range of response, centered around stochiometric (14.7/1) fuel/air ratio.

    If your vehicle had a narrowband O2 sensor and you monitored the O2's input to the ECU, you would see it swinging back and fourth from nearly 0v to nearly 1v in the mad "cat and mouse" game that the older narrowband O2 ECU feedback loop plays.

    With the wideband O2 sensor(s), the ECU simply adjusts fuel flow to keep the O2 input at a constant level (greatly simplified explanation, of course).

    If you want to change the A/F ratio, you'll either need to change the ECU programming, or add/subtract an offset voltage to/from the O2 input.

    Doing so would (of course) void your vehicle's warranty, be in violation of federal emissions laws, along with gravely risking severe and expensive damage to your vehicle's engine and attached components (exhaust, catalytic converter, etc.)

    Without proper instrumentation (such as EGT monitoring at a minimum) the rapid destruction of your vehicle's powerplant is assured.

    This isn't some "cheap and quick" mod that you can just slap together, stuff under the hood, and expect to drive the vehicle to work everyday. There are some "cheap" mods that are out there on the Internet, such as using a pot to change the MAP sensor input. They won't work properly; they'll throw your ECU out of closed-loop mode, forcing it into the default map - or worse yet, cause it to stay in closed-loop mode with invalid inputs.
     
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