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AEM Air/fuel gauge reading high?

Discussion in 'Engine/Tuning' started by mbreaux05, May 16, 2014.

  1. mbreaux05

    mbreaux05 Member Established Member

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    I just installed my aem air/fuel and oil pressure gauges. I installed the widenand sensor right in front of the cats (next to what I presume is the factory wide band). The stock computer gauge reads a constant 14-14.1 while the aem gauge reAds 15.1ish...

    Any idea what is causing this?? The car has the stock tune still.
     
  2. BrianH87

    BrianH87 Member Established Member

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    Aftermarket widebands are usually calibrated for a stoich of 14.7, pure gas. Coyote factory widebands are calibrated for stoich of 14.08, E10 gas. That is most likely your deviation.
     
  3. mbreaux05

    mbreaux05 Member Established Member

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    So which is more accurate?
     
  4. scott_0

    scott_0 Well-Known Member Established Member

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    are you definite you installed the wide band BEFORE the cats? reason I ask is, you cannot actually see the factory wide band in the stock location, assuming you have stock shorty headers, sounds like you installed the wide band after the cats near the rear o2 sensor........
     
    Last edited: May 17, 2014
  5. mbreaux05

    mbreaux05 Member Established Member

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    No I'm sure it's before the cats. It's right at the front of the cats actually. I seen another sensor right in that same area. I assumed that it's the factory wide band.
     
  6. 04sleeper

    04sleeper Runs On "Liquid Gold" Staff Member Super Moderator

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    This.
     
  7. 01bluesnake

    01bluesnake Authorized Vendor Authorized Vendor Established Member

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    My guess is the aem wideband is too close to the cat. There's not much room between the converter and the mounting flanges, so not sure how you managed to weld a bung in there. Unless you pulled stock manifold and welded one in there? That would be a pita though so doesn't make sense and angle would be less than ideal . Post a pic of the aem wideband sensor position, because the only way I can see the AFR that far off is bad placement or after cat. My aem is pretty close to what the stock wideband reads on mine but I have no cats.
     
  8. Shaun@AED

    [email protected] Authorized Vendor Authorized Vendor

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    This is why learning to read Lambda makes things so much easier.
    Factory strategy always targets 1.0 Lambda (unless at WOT, or decel, etc), the programming determines what the Air Fuel ratio is by multiplying the Lambda by the programmed stoich.
    For New Factory Fords, that's 1.0 Lambda * 14.08 Programmed.
    For All aftermarket Air Fuel gauges that's 1.0 Lambda * 14.64 Programmed.

    Your ACTUAL air to fuel ratio is identical (1.0 lambda), it's simply the programming that is different.

    The rest of the deviation can come from the programming as well. There are tables were we can tell the ECU the O2's are not reading correctly. IE, if the programming says that at 2000RPM / low load the O2's are reading 5% richer than actual, the ECU will take that into account and adjust fueling accordingly. An aftermarket wide band will reflect the change (5% leaner) yet the stock ECU will still read 14.1 on the track app (1.0 Lambda).
     
  9. mbreaux05

    mbreaux05 Member Established Member

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    ^^^ made my head spin a little!

    So I guess my air fuel, stock, isint 15.3ish like the aem is reading at idle.
     
  10. JUIC3D

    JUIC3D Boost Junkie Established Member

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    Lambda > *

    Let me see if I can simplify it and have it make sense.

    Stoich is defined as the perfect amount of air/fuel such that the ignition will completely consume all of the fuel. It is the idea combustion that results in the complete consumption of the fuel at hand.

    Stoich is ideal for part throttle and idle as it results in the highest fuel economy.

    AFR is defined as an air fuel ratio. X parts of air mixed with X parts of fuel. Depending on the type of fuel, it takes different parts of air to mix with the fuel to arrive at the stoich for that fuel.

    For example, the stoich in terms of AFR for PURE gasoline is 14.7:1. 14.7 parts of air for 1 part of fuel. When ignited in that ratio, the fuel will be completely consumed and result in the "perfect burn"

    Stoich for E85 (85% ethanol mixed with 15% gasoline) is 9.8:1. 9.8 parts of fuel to 1 part of air.

    See how ethanol stoich is lower than gasoline? That's why the stoich in terms of AFR for E10 (what's available at the pumps now) is LOWER than pure gasoline. The 10% ethanol in gas lowers the stoich for the fuel.



    Now that we've covered stoich, let's talk about lambda.

    Lambda is a % based measurement instead of ratio-based. 1.00 lambda = stoich. .8 lambda=80% of stoich.

    Once you know the stoich of your fuel, figuring out your fueling is so much easier. Lambda simplifies it and says a lambda of 1 for a given fuel is the stoich for that fuel. Values of <1.00 are rich, values of >1.00 are lean.

    Lambda of 1.00 for pure gasoline=14.7 afr
    Lambda of 1.00 for E10=14.1 afr
    Lambda of 1.00 for E85-9.8 afr


    The stock tune commands .82 lambda at WOT which in terms of AFR would be 14.1*.82=11.56 AFR.


    You can either do math calculations in your head to figure out air fuel ratio OR you can convert to "lambda thinking" and forget AFR altogether. Lambda of 1=stoich, and anything lower is rich, higher is lean.

    1 lambda at part throttle and idle and .77 lambda at WOT for me. It's that simple.


    Hope that helps!
     
  11. mbreaux05

    mbreaux05 Member Established Member

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    That's for taking the time to explain all this!. I definitely understand it better now.

    I'll try to get of a picture of my sensor as soon as I can.


    If anyone has cats with an aftermarket wide band, can you post pics of your sensor location??
     

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