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[FAQ] Understanding How A/F Gauges Work

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Old 10-31-2004, 06:50 AM
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Default [FAQ] Understanding How A/F Gauges Work Part 2

I desided to make this thread because I know thats alot of people, like myself before i got my own and went tuning. So here is a little info i know and please if you know something i dont or i said something wrong correct me, because, like everyone else, im here to learn.

Ok first off what is a A/F Gauge :


(Same type i have but mines white, wish i saw this one cause i would have got it, oh well im over it )

An A/F gauge gives you a nice little light show that tells you weither or not your running rich or lean or Stoich reading the signals from the o2 sensor.

Now What is an o2 sensor?



An o2 sensor tells your ECU if your running rich or lean and tells your ECU how to counteract the way your motor will run, with its reading. (Kind of like a MAP sensor but not really, MAP sensor understanding will be on another thread, for another time)

Usually when you hook up an A/F Sensor you want to hook it up to a wideband o2 sensor because it will give you a better reading. But if your like me and take long trips frequently and want to make sure your not wasting gas you would get a A/F gauge to give you an idea of how your driving is going (or you just might like a light show, i dont know).

What is a wideband o2 sensor?



Now those are the 2 basic objects used for an A/F gauge (one is a super object to get the job done right ), Now this is what each one does and how it works.

A/F gauge: The A/F gauge gives you the reading of the o2 sensor like i said before but how does it do it. It sends you the info in forms of colors (except for some which give you number readings like the wideband), to let you know if your running rich or lean and what not. Now know when you are tuned or if your car is stock sometimes you wont even see the light show up. From my understanding thats because your injectors shut off or are on idle where its not enough to let the o2 sensor read anything.

o2 sensor: A little sensor that gives the car readings of how its running. Edited to Shaundrake's post . That is because the o2 sensor isnt getting a good reading of mixture in the air and reads it very rich, also when the o2 sensor is fully warmed up thats when your car will be warmed up as well. o2 sensor is also a key object used for tuning because you use A/F for tuning. I dont understand why people take out there o2 sensor because thats the stupidest thing you could do, your car would run like **** just to save 10 bucks for a bung to be welded on. Not worth it IMO. Also for us Cali people we need it for smog.

Pre OBD2 cars have 1 o2 sensor that is usually located before the cat. OBD2 cars and up have 2 (maybe more on different cars) that are usually on the exhaust manifold and right before the cat.

Wideband o2 sensor: Now this o2 sensor i dont really know to much about because i dont have the money to run one (i cant save money that long without spending it on something else ) But i know theres members on here (Like Ricey) that are running this. So guys please chim in on what i say wrong or put out more info yea?

Ok from what i know about the wideband is that it reads in numbers instead of pretty little lights, same as if you went to a dyno. This is because it gives you a better accurate number. The numbers are set (usually) from 10 (ive been past there before ) to 18. The higher the number the leaner you are and the lower the number the richer you are. Usually people want there cars to run around 14.7. But <FONT SIZE="3">EVERY CAR IS DIFFERENT!!!!!</FONT> so your motor might want to run richer then 14.7. Wideband gives you a good reading because of the numbers used to show you how your running. Thats about all i know about wideband other then the price which is about a 1000 dollars (might have changed since last time i thought of getting it.)

Well thats my little right up of it. If i can think of anything else ill add, if im corrected then ill correct. This isnt a tuning thread (although not a bad idea) this is just a thread to inform people how it works and what it does. Add on!!!!!


Modified by Luserkid at 8:03 AM 10/31/2004


Modified by Luserkid at 11:38 AM 10/31/2004


Modified by Luserkid at 11:02 PM 10/31/2004


Modified by Luserkid at 11:03 PM 10/31/2004
Old 10-31-2004, 06:56 AM
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Default Re: [FAQ] Understanding How A/F Gauges Work Part 2 (Luserkid)

Good writeup Luserkid!

I've always wonder if my B16 has problems with the o2 sensor. I know 02 sensors get defective and sometimes don't throw any code at all.

*Oh yeah don't forget to fix the wideband 02 sensor pic.
Old 10-31-2004, 07:03 AM
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Default Re: [FAQ] Understanding How A/F Gauges Work Part 2 (handa)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by handa &raquo;</TD></TR><TR><TD CLASS="quote">*Oh yeah don't forget to fix the wideband 02 sensor pic.</TD></TR></TABLE>

Good looking out I wrote it all up on notepad and just through it on so i didnt check the pics.

Old 10-31-2004, 07:58 AM
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Default Re: [FAQ] Understanding How A/F Gauges Work Part 2 (Luserkid)

i always thought that the higher the number the leaner and the lower the number the richer?
Old 10-31-2004, 08:21 AM
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you can get widebands for like 350 and cheaper now.
Old 10-31-2004, 08:56 AM
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Default Re: (shrug)

Yeah widebands are a lot cheaper than a grand now. The AEM gauge type wideband is arguably the best and that goes for around $550. This type of wideband is different and not as scientificallly accurate as true widebands found on a dyno, but they are extremely useful nonetheless.

Like he said you got your lean/rich numbers mixed up. 12 is the richest I see on most cars and when you go into the high 15s you risk detonation from running lean. Most of the time you want to hover close to 14.7, a stoich mixture and one that Honda engines make a great deal of power at, until you reach high RPM at which point you want to be going rich for safety.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">To work the car needs to be fully warmed up. When you start your car in the morning (or in my case, all the time ) your car will most likely shoot to 1500 to 2k to some cases, like me, 2500 rpm to warm itself up. That is because the o2 sensor isnt getting a good reading of mixture in the air and reads it very rich, also when the o2 sensor is fully warmed up thats when your car will be warmed up as well</TD></TR></TABLE>

This whole paragraph is wrong. I'm not trying to be mean but you're not qualified to write this article. You're misleading people. Just go to the manufacturers websites and do youre reading. I wouldn't believe anything I read on Honda Tech.

The O2 sensor, not the car, needs to be warmed up. 4 wire O2 sensors warm up rather quickly because they have a heater.

Your car sounds like it has a problem with the FITV. Your car shouldn't be over 1800RPM or so to warm up. This process has nothing to do with the O2 sensor but is completely dependent on water temp. The reason why youre running rich during warm up is because your ECU is purposely running rich to warm your engine up. Also, because the intake air is so cold, the fuel does not atomize, so your engine has to compensate by shooting more fuel.

During WOT, your AF gauge should be pegged to the rich side. This is because your ECU goes into open loop mode and uses a predetermined fuel map. Leaning this area out with an aftermarket ECU can result in large power gains, but should only be done on a dyno by qualified personnel.

During cruise or zero throttle deceleration, your AF gauge should be pegged lean. This is because the ECU turns off the injectors for deceleration, and purposely runs lean for fuel economy for cruising.

AF gauge with a narrow band O2 sensor is useful for telling you if you have a lazy O2 sensor, or functions as an idiot light so that you can back off and save your engine should you run lean at high loads and RPM. It's not useful for tuning unless you are tuning strictly for 14.7, which is the only value a narrow band O2 sensor is accurate at reading.

As you said, an O2 sensor is not strictly a smog device. It's just like a MAP or IAT sensor giving your ECU the information it needs to determine the right injection times. Simply running rich does not increase power, and running in open loop certainly does not increase power.

It's not as easy as swapping your narrow band O2 for a wideband. Until recently, you couldn't hook up your aftermarket wideband to your ECU, so you had to have a seperate bung welded in and use both. Your original O2 runs to the ECU, and your narrow band runs to your gauge. Now there are brands like AEM that can output a signal appropriate for your stock ECU.
Old 10-31-2004, 09:00 AM
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Default Re: (shaundrake)

nice write up man.. very informative
Old 10-31-2004, 10:37 AM
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Default Re: (shaundrake)

Shaun thanks for the info, like i said im here to learn just like everyone else so if some of my info is wrong correct me.

I got my car tuned to high 13s up until boost then it goes down to mid 12s. But my motor likes it right here which is why i said all motors are different.

Im changing that part that you quoted and going to say to look at your post.

Also i didnt know that wideband was that cheap now. I might look into getting one again.
Old 10-31-2004, 11:39 AM
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Default Re: (Luserkid)

good info to get some of the basics down....

here's a little to expand on wideband/air-fuel, as i know enough of this stuff to get by, but no actual experience. and that post about search.... its right...


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Hondaddict &raquo;</TD></TR><TR><TD CLASS="quote">

First of all, your stock O2 sensor outputs 0-1 Volt reference to your ecu. The higher the voltage, the richer the air/fuel ratio. The problem with a narrowband is that it has an "accuracy window," which means it is accurate ONLY from 14.3:1 - 15.3:1!!! (To make this easier to read from here on I will write this as: 14:1-15:1)

Here is an illustration to show the limit of the stock narrowband sensor.


The stock sensor is incapable of measuring richer than 14:1, or leaner than 15:1! Your Autometer gauge would read a full green LED, FULL RICH at any air/fuel ratio richer than 14.3:1!!!! Now how can a gauge with a sensor that can measure air/fuel ratios from 14:1-15:1 be used when you are aiming for 12.0:1? The stock sensor is incapable for high performance tuning!

The solution:
You don't have to throw away your Autometer (or similar) gauge. PLX Devices has a product to use the Autometer gauge with a wideband sensor. Using any M-series wideband controller (PM me for the best price) and a $35 converter, your Autometer gauge can read air/fuel ratios from 10:1-20:1!!! Problem solved.

Here is an illustration of the output of the PLX wideband sensor:


What it comes down to is that a "wideband" sensor must be used, in conjunction with a controller to measure air/fuel ratio. A good wideband sensor can read from 10:1-20:1, and in my experience a "digit display" is the best where LARGE digits display the air/fuel ratio so you can see it.

Hope this clears things up, I really hope people can understand now why they can't use their autometer gauge for full throttle conditions!

</TD></TR></TABLE>

great article by hondaddict... i've cut it up to highlight some of the important parts...

entire thing can be found here...
https://honda-tech.com/zerothread?id=1001592

-pauL
Old 10-31-2004, 11:54 AM
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PLX has a device out to make a/f gauges actually useful, its kinda cool


Old 10-31-2004, 12:27 PM
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Default Re: (WrongWD)

where can i find that, is it cheap, cause if it isnt u could just get a wideband lol, thanks
Old 10-31-2004, 03:24 PM
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WOW im in someones sig! i read that and said ahah thats funny, then saw that i wrote it. god damn im the ****.
Old 10-31-2004, 04:19 PM
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Default Re: (shrug)

I think the first thing in the FAQ should be a clear paragraph with the narrowband output graphs posted explaining why any a/f gauge hooked up to a narrowband 02 is simply a blinky light toy, nothing more.
Old 10-31-2004, 04:23 PM
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Default Re: (Prod)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Prod &raquo;</TD></TR><TR><TD CLASS="quote">I think the first thing in the FAQ should be a clear paragraph with the narrowband output graphs posted explaining why any a/f gauge hooked up to a narrowband 02 is simply a blinky light toy, nothing more. </TD></TR></TABLE>

Almost completely agree, except that the lightshow a/f gauge does indicate if your o2 sensor is doing ANY kind of monitoring
Old 10-31-2004, 09:39 PM
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Default Re: (senpai)

when you said your motor likes it, i hope you mean that on the dyno, the graph went up. not that youre turning a fuel pressure **** in your garage or something.
Old 10-31-2004, 09:47 PM
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Default Re: (shaundrake)




Im not that stupid to tune in my garage on a butt dyno. And no adjustible FPR, its on 440cc's
Old 10-31-2004, 09:54 PM
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Default Re: [FAQ] Understanding How A/F Gauges Work Part 2 (1993sir05)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 1993sir05 &raquo;</TD></TR><TR><TD CLASS="quote">i always thought that the higher the number the leaner and the lower the number the richer? </TD></TR></TABLE>

pretty sure thats right,

its an AIR FUEL RATIO not just a number,
so remember, a larger number ratio is actually larger,
like 1/4 is a bigger chunk than 1/16

or some ****..
Old 11-01-2004, 02:19 AM
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<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Soccerking3000 &raquo;</TD></TR><TR><TD CLASS="quote">where can i find that, is it cheap, cause if it isnt u could just get a wideband lol, thanks</TD></TR></TABLE>

PLX sells it directly from their website.

It isn't any cheaper than a wideband, simply because it isnt there to substitute, just supplement so you can always keep an eye on your a/f
Old 11-01-2004, 03:57 AM
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Default Re: (WrongWD)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by WrongWD &raquo;</TD></TR><TR><TD CLASS="quote">

PLX sells it directly from their website.

It isn't any cheaper than a wideband, simply because it isnt there to substitute, just supplement so you can always keep an eye on your a/f</TD></TR></TABLE>

Actually, all that item does is allow you to hook up a wide-band signal to a common Autometer A/F gauge. If you're using the stock O2 sensor, it won't help you at all.

"The M-Series Narrowband to Wideband Gauge Converter is a small inexpensive device used to connect between the M-Series' wideband output signal and the input signal to any AutoMeter air/fuel ratio gauge....Must be used with PLX M-Series Wideband controller."
Old 11-01-2004, 04:47 AM
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i know thats why i said it isnt any cheaper than a wideband setup and that it is a supplement to it.
Old 11-01-2004, 05:07 AM
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Yeah just to let you know, 14.7 is great and all, and that makes the most power, but thats without thinking about the cooling the fuel has to do inside the chamber, to keep from detonating....just a little tidbit of info.
Old 11-01-2004, 06:58 AM
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Default Re: [FAQ] Understanding How A/F Gauges Work Part 2 (slow poke)

Jesus tap dancing titty ******* christ it was that bad.

Did any of the stuff that i wrote (which i thought i knew but now standing correct) was right, or somewhat close?

**** i dont know beans about A/F sorry guys.

But on the plus side the people that do know are chiming in
Old 11-01-2004, 07:34 AM
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Default Re: (xerox445)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by xerox445 &raquo;</TD></TR><TR><TD CLASS="quote">Yeah just to let you know, 14.7 is great and all, and that makes the most power, but thats without thinking about the cooling the fuel has to do inside the chamber, to keep from detonating....just a little tidbit of info.</TD></TR></TABLE>

In all reality, 14.7 is not where any setups make the most power from what I've seen.

~14.7 is what I try to tune the idle for. That's it. Idle and partial throttle cruising. For N/A setups, they seem to want to make the most power between 13.0-13.8, and FI seems to like 12.0-12.8 (agian, this is just what I've seen from tuning cars). This is where the plugs are a healthy brown and they run well and make power.


Just my .02.
Old 11-01-2004, 08:02 AM
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Default Re: (Ricey McRicerton)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Luserkid &raquo;</TD></TR><TR><TD CLASS="quote">Jesus tap dancing titty ******* christ it was that bad.

Did any of the stuff that i wrote (which i thought i knew but now standing correct) was right, or somewhat close?

**** i dont know beans about A/F sorry guys.

best thing ive heard him say

But on the plus side the people that do know are chiming in </TD></TR></TABLE>

thank you to those that contributed very useful and helpful info
Old 11-01-2004, 08:38 AM
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Default Re: (WrongWD)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by WrongWD &raquo;</TD></TR><TR><TD CLASS="quote">i know thats why i said it isnt any cheaper than a wideband setup and that it is a supplement to it.</TD></TR></TABLE>

It is a wideband setup. The device simply takes the wideband output from one of PLX's wideband controllers and allows it to be displayed by an Autometer gauge. The unit still requires a PLX wideband controller and a compatible wideband O2 sensor.
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