Engine 1st Gen 2nd Gen 3rd Gen A resistor to fool the O2 sensor?

Discussion in 'General Technical Questions and Answers' started by Whine not Walnuts, Oct 6, 2018.

  1. Whine not Walnuts

    Whine not Walnuts Active Member
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    Up until last week I had a high flow 200 cell catalytic converter attached to my 4-2-1 header via a doughnut connection. When I worked on my transmission recently I pulled the high-flow off and installed a used OEM cat that I bought from CL as I have my yearly inspection coming up that includes emissions.

    The high-flow in conjunction with a O2 extender worked well for about 6 months but then the precious metals must have dissipated to the point that even with the extender codes started being thrown. I have done allot of research on cats and aware of the "magic" dimension for long life and how the matrix folding impacts life span as well. With the high-flow attached to the 4-2-1 and the JCW exhaust I had a great tone and the pops/burbles were quite nice, not overly loud.

    Back to the O2, it does not really sense oxygen levels but rather the temperature of the exhaust as it exits the converter. If the engine mixture is rich then there will be more fuel, hydrocarbons, and the precious metals within the converter matrix will "burn off" this excess via a chemical reaction that creates heat. More unused fuel in the exhaust, the hotter the post converter exhaust stream. A lean fuel mixture will have less unused fuel so the the post converter stream will be cooler.

    I am thinking that if you know what impedance range the ECU is looking for a resistor in conjunction with a capacitor may do the trick.

    Something like the picture below. O2 trick.jpg

    Anybody had success with this?
     
  2. Dave.0

    Dave.0 Helix & RMW Powered
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    This looks interesting for those running OEM o2’s.

    I am running OEM o2’s but my ViPEC ECU controls everything with the Innovative wideband O2 I had installed into my RMW street header.
     
  3. Whine not Walnuts

    Whine not Walnuts Active Member
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    I like the sound of the high-flow and my butt says its quicker so I will be putting it back on after my inspection. The CEL is a PIA as I don't like driving around with a the light on as you don't know if something else pops up. I don't know if this is different then "eliminating" the post stream O2 and then whether there are long term adverse affects.

    I need to do more review.
     
  4. Whine not Walnuts

    Whine not Walnuts Active Member
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    From what I can find this should eliminate the codes. Below are the part numbers that you can get on Radio Shack or Amazon. Appears the biggest issue is keeping both dry and away from the muffler/cat. If I did it I would run some travelers up into either the ABS or the Brake Master Cylinder bays.

    Also appears to work only on narrow band O2 sensors that the OEM system has.

    A 1 Microfarad (1μF) Capacitor - RadioShack part number 272-1055
    A 1 Mega ohm (1MΩ) Resistor - RadioShack part number 271-1134
     
  5. vetsvette

    vetsvette MINI Alliance Ambassador
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    Solder the connections and use some good heat-shrink and you should be good.
     
  6. MCS02

    MCS02 Moderator
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    Where did you get the high flow CAT? I am going to pull my CAT because I believe it is bad and have a muffler shop make me a test pipe to run till I gel a new CAT
     
  7. Whine not Walnuts

    Whine not Walnuts Active Member
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    OK, first let's talk about cats. The rule is thumb is the cheaper the price, the less precious metals to act as catalyst agents and that many will not hold up under the forced induction heat/pressures that forced induction produces. The space where the cat can be installed also is a factor. The factory cat is about 5.25 inches (diameter) on the Gen1. There are allot of high flow cats out there but longevity can be linked to the overall diameter and a minimum number that is discussed is 130 mm (5.1"). Many "green" highflows are 6" in diameter so unless they are very short they may hit part of the heat shield or body/frame.

    The matrix within the cat comes in either metallic or ceramic. There is some discussion that the metallic matrix is better for forced induction but the OEM cat is ceramic.

    Cats matrix.jpg

    Then the metallic matrix can be folded two different ways. The first, and least expensive method, is the "paper towel" type roll above. The "s-fold" like below is more expensive and many of the European exotic cars have this "s-fold" matrix that is said to stay together better.

    S fold matrix.jpg

    Last is the number of cells that the matrix has. The higher the cell count, the OEM is 400, the more resistance and more "muffled" the sound. The last I knew Jan at RMW is using a Vibrant GESI high flow cat that is a 300 cell count. Kooks in North Carolina makes a 300 cell high flow that is rated for 900 HP forced induction. This unit is the "magic" 130 mm in diameter and when I spoke to them they said their unit would withstand numerous track days.

    I went with an Eastern metallic matrix unit with a 200 cell count. I found that Yonaka, many Hondas use, has a 100 cell unit with a "s-fold." Remember the lower the cell count, the less resistance and the louder the sound. The Eastern 200 cell with my JCW exhaust was really sweet, similar to a 4 cylinder motorcycle sound. If Sully can get the video function up I will post some vids. The Eastern and the Yonaka are 100 mm/4" units and are usually less than $100. The green units such as what Jan uses or Kooks makes are over $300. This cost is the result of the amount of precious metal in the matrix.

    I am thinking the cheaper cats through time consume the precious metals up and then are basically just a screen inside a metal tube. With no precious metals there is no "reaction" and therefore the O2 sensor is not sending proper voltage parameters back to the ECU. The precat narrowband O2 modulates between the 0.1 and 0.9 volts where the postcat sensor either sees around 0.05 volts in a rich state or 0.9 in a lean state. This makes me think that the O2 sensor is like a resistor where the richer mix that has a greater reaction/more heat allows less voltage to pass then when the mixture is lean/less heat that would pass more voltage.

    Hopefully this thread will awaken a static member that has allot more mental functions then I have but has not been participating. About 1:45 in the below clip.

     
  8. Dave.0

    Dave.0 Helix & RMW Powered
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    Also cover any connections in silicon and let it dry before you heat shrink it.
     
  9. Sully

    Sully Administrator
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    For my RzRs which spend lots of time in water, heat shrink is the key. I’ll look up the ones I buy. They work great.

    Regarding the rest of the article, just learned a lot about cats.. :)
     
  10. DneprDave

    DneprDave Well-Known Member
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    I bought some heat shrink tubing at Harbor Freight that has sealer inside the heat shrink, it oozes out the ends when heated and shrunk.
     

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