Wideband/Narrowband AFR
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This is a discussion on Wideband/Narrowband AFR within the Tuning: Electronic Engine Management forums, part of the Tech & Modifying & General Repairs category; So i decided to start this thread after a little motivation from Sinister. This may help out people in the ...

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    Registered User wrx0131's Avatar
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    Wideband/Narrowband AFR

    So i decided to start this thread after a little motivation from Sinister. This may help out people in the future looking to know the difference between a wideband afr and a narrowband afr.

    Quoted by Sinister:

    Narrowband only reads between 11 and 21.

    A proper tune will be riding the line of 11.... so you'll never know if you're tuned perfectly or if it's maxed out.

    A narrowband is necessary for the computer to be able to maintain a stoich air to fuel mixture. (14.7). But Stoich for certain fuels can be as low as 9 (E85) or lower if you're running straight alcohol. The 14.7:1 is calculated in closed loop, but as soon as you're wide open throttle, the ECU moves to an open loop system and no longer uses the narrowband AFR.
    what does a wideband read?
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    UnBanned Sinister's Avatar
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    Quote Originally Posted by wrx0131 View Post
    what does a wideband read?
    Here's a very good quote from Wikipedia. I couldn't have said it better. And it explains the voltage part which I was going to stay away from... lol.


    there are two types of sensors available; narrow band and wide band. Narrow band sensors were the first to be introduced. The wide band sensor was introduced much later.
    A narrow band sensor has a non-linear output, and switches between the thresholds of lean (ca 100-200 mV) and rich (ca 650-800 mV) areas very steeply.
    Also, narrow band sensors are temperature-dependent. If the exhaust gases become warmer, the output voltage in the lean area will rise, and in the rich area it will be lowered. Consequently, a sensor, without pre-heating has a lower lean-output and a higher rich-output, possibly even exceeding 1 Volt. The influence of temperature to voltage is smaller in the lean mode than in the rich mode.
    A "cold" engine makes the sensor switch the output voltage between ca 100 and 850/900 mV and after a while the sensor may output a switch voltage between ca 200 and 700/750mV, for turbocharged cars even less.
    The Engine Control Unit (ECU) tries to maintain a stoichiometric balance, wherein the air-fuel mixture is approximately 14.7 times the mass of air to fuel for gasoline. This ratio is selected in order to maintain a neutral engine performance (lower fuel consumption yet decent engine power and minimal pollution).
    The average level of the sensor is defined as 450 mV. Since narrow band sensors cannot output a fixed voltage level between the lean and the rich areas, the ECU tries to control the engine by controlling the mixture between lean and rich in such a sufficiently fast manner, that the average level becomes ca 450 mV.
    A wide band sensor, on the other hand, has a very linear output, 0 - 5 V, and is not temperature dependent.
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    UnBanned Sinister's Avatar
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    Dummed down version?

    Narrowband isn't as accurate because temperature influences the reading. But it's effective enough that the engine is able to maintain approximately 14.7:1 Air to Fuel Ratio. This is stoich... where you get the best gas mileage.


    Wideband is accurate from 0 until it's maxed out. You don't care about what it maxes out at because you should never be that lean. During tuning you may end up anywhere between 8 and 13 AFR depending on many factors, but the general consensus is ~~ 11:1 AFR under full boost. You'll see tuners anywhere from 10-12 though.
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    Registered User wrx0131's Avatar
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    Quote Originally Posted by Sinister View Post
    Dummed down version?

    Narrowband isn't as accurate because temperature influences the reading. But it's effective enough that the engine is able to maintain approximately 14.7:1 Air to Fuel Ratio. This is stoich... where you get the best gas mileage.


    Wideband is accurate from 0 until it's maxed out. You don't care about what it maxes out at because you should never be that lean. During tuning you may end up anywhere between 8 and 13 AFR depending on many factors, but the general consensus is ~~ 11:1 AFR under full boost. You'll see tuners anywhere from 10-12 though.
    nice!

    thanks for the info

    If I remember my car reads about 10.3 under full boost....maybe in the 11s, i dont really remember lol
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    UnBanned Sinister's Avatar
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    Sure... If anyone else has more to add, I'm a scooby newbie
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    Quote Originally Posted by Sinister View Post
    Wideband is accurate from 0 until it's maxed out
    Widebands will usually only read down to 10:1 gasoline AFR or close to .68 lambda.

    Since a wideband is essentially measuring lambda and not gasoline AFR's however, it can be used even in applications with E85 where the stoich is 9.8:1 in gasoline AFR's and WOT mixtures can be in the high 7's.

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    Quote Originally Posted by xsnapshot View Post
    Widebands will usually only read down to 10:1 gasoline AFR or close to .68 lambda.

    Since a wideband is essentially measuring lambda and not gasoline AFR's however, it can be used even in applications with E85 where the stoich is 9.8:1 in gasoline AFR's and WOT mixtures can be in the high 7's.
    good point!
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    Quote Originally Posted by xsnapshot View Post
    Widebands will usually only read down to 10:1 gasoline AFR or close to .68 lambda.

    Since a wideband is essentially measuring lambda and not gasoline AFR's however, it can be used even in applications with E85 where the stoich is 9.8:1 in gasoline AFR's and WOT mixtures can be in the high 7's.
    Depending on the sensor some do read down alot lower than 10:1 gasoline.My LC-1 will read down to 7.5:1.
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    Quote Originally Posted by Donkey View Post
    Depending on the sensor some do read down alot lower than 10:1 gasoline.My LC-1 will read down to 7.5:1.
    I believe some of the higher end stationary units will read pretty low as well.
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    Admiral Ackbar the 1st mycologist's Avatar
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    The temperature isn't the important bit IMO - it primarily sounds to change the end line voltages for lean and rich but it would still be worthless for WOT tuning. It is the narrow band switching. It is a lean rich switch and nothing else is accurate. Sometimes a picture is worth a thousand words:
    Narrowband voltage switch - you are either lean, rich, or accurate from ~14-15:1


    Wideband linear voltage - you can read it across the scale accurately


    This is critical for tuning because of the rich range required to prevent detonation - as explained you are not targeting stoich.
    Last edited by mycologist; 07-07-2009 at 02:58 PM.
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    thats a good set of pictures for the new guys who keep trying to hook up air fuel gauges to their stock oxygen sensors. Maybe a link (or the pictures themselves) could go in one of the FAQ's somewhere to help people understand?

    And someone correct me if i'm wrong here, but isn't the stock manifold-located oxygen sensor some sort of different oxygen sensor? I know it seems to stay on par with my wideband down to about 12.5:1, and seems to be able to read up to 16:1 fairly accurately. Granted there is usually a .2 AFR point of difference between the two. This may be due to the fact that one is pre-turbo, and one is post-turbo.

    Also what would be an acceptable solution for us wideband users with EWG thats VTA? It should make the sensor show lean correct?

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    Admiral Ackbar the 1st mycologist's Avatar
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    Quote Originally Posted by xsnapshot View Post
    thats a good set of pictures for the new guys who keep trying to hook up air fuel gauges to their stock oxygen sensors. Maybe a link (or the pictures themselves) could go in one of the FAQ's somewhere to help people understand?

    And someone correct me if i'm wrong here, but isn't the stock manifold-located oxygen sensor some sort of different oxygen sensor? I know it seems to stay on par with my wideband down to about 12.5:1, and seems to be able to read up to 16:1 fairly accurately. Granted there is usually a .2 AFR point of difference between the two. This may be due to the fact that one is pre-turbo, and one is post-turbo.

    Also what would be an acceptable solution for us wideband users with EWG thats VTA? It should make the sensor show lean correct?
    The graph is generic to illustrate the distinct response, it is not a WRX graph. I based the range of accuracy off the graph to illustrate how to read it. The range of accuracy for the WRX sensor I don't exactly know, but your numbers sound familiar. An actual WRX graph would be better for a sticky or link as a reference.

    I would like to hear what others say about the EWG situation.
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    Admiral Ackbar the 1st mycologist's Avatar
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    Also, I believe your fuel trims will change if you use e85 within the range they are allowed. This would seem to indicate that the stock sensor is reading lambda as well.

    Also, your > fuel trim is based on the stock sensor, and it will carry over into open loop (at least in some cases) IIRC.
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    Quote Originally Posted by mycologist View Post
    Also, I believe your fuel trims will change if you use e85 within the range they are allowed. This would seem to indicate that the stock sensor is reading lambda as well.

    Also, your > fuel trim is based on the stock sensor, and it will carry over into open loop (at least in some cases) IIRC.
    Correct. Stock sensors read lambda. Actually i'm pretty sure all oxygen sensors read lambda.

    I think your right on the learned fuel trim carrying over into open loop. By > did you mean positive?

    I noticed this evening while tuning that my factory wideband was pegged at 11.13 (its lowest reading possible) while my wideband was showing 11.8:1. I know its way out of its efficiency area and that pre-turbo the sensor can be affected by the varying backpressure, but i'm thinking im actually running much richer than 11.8 (external wastegate was open) I need to address this as being richer than the lambda equivalent of a gasoline AFR of 11.8, is unnecessarily rich on E85. I just had it set at 11.8 to get my boost tuned right, before attempting to lean it out any.

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    Quote Originally Posted by xsnapshot View Post
    thats a good set of pictures for the new guys who keep trying to hook up air fuel gauges to their stock oxygen sensors. Maybe a link (or the pictures themselves) could go in one of the FAQ's somewhere to help people understand?

    And someone correct me if i'm wrong here, but isn't the stock manifold-located oxygen sensor some sort of different oxygen sensor? I know it seems to stay on par with my wideband down to about 12.5:1, and seems to be able to read up to 16:1 fairly accurately. Granted there is usually a .2 AFR point of difference between the two. This may be due to the fact that one is pre-turbo, and one is post-turbo.

    Also what would be an acceptable solution for us wideband users with EWG thats VTA? It should make the sensor show lean correct?
    The stock is kinda a wideband with a very limited range.Sad part about that is the ECU doesn't use O2 feedback at WOT as it goes into "openloop" and relies on the MAF sensor for the primary fueling data.
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