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a/f ratio question

Discussion in 'The Garage' started by g_mo, Apr 26, 2005.

  1. g_mo

    g_mo 1/2 ton status

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    can i use 4 wire 02 sensors, or wide range a/f sensors to monitor a/f ratio on a carbed 350? if wired to a digital a/f ratio gauge will the gauge display what the sensors are reading, or will i need to monitor the sensors with a voltmeter?
     
  2. Thunder

    Thunder 3/4 ton status

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    Autometer makes AF ratio guages that work with any 02 sensor. Just plumb A 02 sensor in your exhaust pipe near the manifold hook it up to the guage as instructed and you are good to go. The heated 3 or 4 wire sensors give the best readings. But the guages will also work with single wire 02 sensors.
     
  3. ntsqd

    ntsqd 1/2 ton status

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    Wide band O2's are 0 to 5VDC, 'normal' O2's are 0 to 1 VDC. A gauge designed for a 'normal' O2 will be confused or even hurt by a wide band.
    I think I posted it here a long time ago. Search O2 readers/gauges as I have a simple reader circuit that costs about $30 at RadioShack for the components.
     
  4. Mad-Dog

    Mad-Dog 1/2 ton status

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    4 and 5 wire sensors are for wide-band applications (very expensive),
    a simple 3-wire heated sensor will work fine for you.
    heated sensors are far more accurate than non-heated sensors.
    I use a Halmeter AF/30 unit with a 3-wire heated sensor (check out the web page for pics of the unit in dash.
    It costs around $275 but it is very accurate, 3-wire sensors have 2 blacks and a white....the white is signal and the 2 blacks are for the heater which is bi-polar and does not care which of the blacks go to power or ground.
     
  5. g_mo

    g_mo 1/2 ton status

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    i have access to alot of 4 wire 02 sensors. they are used and have bad heater circuits, but i am told the sensor is still good. could these be used?
     
  6. Mad-Dog

    Mad-Dog 1/2 ton status

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    yes, with a wide-band decoder...
    you don't need to spend that kinda money bro, forget the 4-wire sensors and keep it simple man.
    a single wire sensor will work for you and it will help you calibrate the jetting just fine.
     
  7. Triaged

    Triaged 1/2 ton status

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    All the wideband O2 sensors I have ever seen are 5-wire. To my knowlage there does not exist a 4-wire WBO2 sensor.

    The 4 wires are:
    Sense Cell Voltage
    Sense Cell Ground
    Heater +
    Heater -

    If you wanted something real simple you could just watch the voltage with a volt meter. Stoich. is around 450mV, lean is lower, & rich is higher.

    ntsqd,
    What did you do for a circuit?
     
  8. sled_dog

    sled_dog 1 ton status

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    4 wire is just a grounded/heated O2 sensor. 5 wire is wide band.

    A/F guages show what the sensor is reading.... sort of. They put the voltage into a LED display. My summit one cost like $20. I could have built one, and should have. Or just put a voltmeter on the output wire.
     
  9. g_mo

    g_mo 1/2 ton status

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    thanks for the info. i am going to run the 4 wires sensors and watch them with a voltmeter.
     
  10. ntsqd

    ntsqd 1/2 ton status

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    I was told that .7 to .75 is the leanest you want to be w/o a computer. Any closer to Stoich and it'll detonate too easily. The Lamba vs. Voltage curve of a narrow band O2 sensor is quite steep in that area.

    I've built several of these readers, but I do not consider them anywhere close to equal to a Horiba (sp?) or similar tool. They do work well enough to get an idea of what's going on.

    EDIT: Realized that this diagram is NFG unless you know something about the LED output. It is a ten segment LED assembly. When you're where you want to be (i.e. near Stoich) the first five segments will light up. It's been a while since I used mine, by I recall that richer = more lights. You can plug this in, in parallel, to a computer controled engine and watch the computer see-saw the A/F back and forth across the ideal.

    O2SENS.jpg
     
    Last edited: Apr 30, 2005

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