Air fuel ratio using voltmeter

Chuck Schneider · Post by **Chuck Schneider** » Tue May 22, 2001 4:58 pm

Does anyone know what voltage corresponds to what air fuel ratio using a voltmeter on an 02 sensor. I have a book and all it says is that 1 volt is rich and 0 volts is lean and .5 is stociometric. Thanks for any help

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GDRBO · Post by **GDRBO** » Tue May 22, 2001 8:34 pm

The only thing that is accurate at any given point is that .5 = 14.4:1 AF ratio. Anything on either side only indicates rich or lean but not by how much. .4 or .6 might indicate you are close but another .1 is way down the scale as it drops off very rapidly. You can't say that .4 needs 2 jet sizes and each .1 after that needs 2 jet sizes as well.

Chuck Schneider · Post by **Chuck Schneider** » Tue May 22, 2001 9:09 pm

If it isn't accurate then how does an air fuel gauge work?

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bruce · Post by **bruce** » Tue May 22, 2001 9:11 pm

In my experience, you can't get it to run at stoic. It'll either run rich or lean. When you are close, it will swing wildly on either side. Get it to run stable at .85V.
Note, these observations are with carbs.

Steve Arndt · Post by **Steve Arndt** » Wed May 23, 2001 8:45 am

How does an air/fuel gauge work?
They don't, to put it simply. People that buy a 20 dollar gauge and 20 dollar sensor and expect it to tell them everything are in for a surprise. However, the people that buy the stuff knowing it is telling them the truth at 14.4, and only a wild ass guess everywhere else are going to benefit.
You may ask why are these sensors such crap outside of stoich? They are designed that way for a reason. Catalytic converters work best in this range. They designed the sensors to work good in that range for when computer run in closed loop, to keep the engine as close to where the cat can do its dead. It is fairly simple.

If you want a tool to tell you air/fuel ratios then you need a wide band O2 sensor and interface. M&W, Heigo, Autronic, etc. They start at about 800 bucks.

Veepster · Post by **Veepster** » Wed May 23, 2001 10:25 am

from a lot of experience with an O2 and a voltmeter and a VW you don't want stoic.....they do not like to run that lean...

it is a great assistance to tuning but it is not the holy grail...I have been able to track down flat spots and have used mine for general tuning guidance and reassurance.....It is worth every penny!....$25 for the O2 and a digital voltmeter

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Peace.............BartG www.teamgodspeed.com

Chuck Schneider · Post by **Chuck Schneider** » Wed May 23, 2001 4:37 pm

Steve with the exception of idle and very low load conditions you never want to see 14.7 you get peak acceleration at between 12 and 13 to 1. I just need to know what voltage equates to what number. I have one of those Cb guages but you have to use a jap o2 sensor. I am tuning a SDS efi turbo motor and I am using a bosch o2 sensor. THe Bosch is incompatable with the cb guage. I tuned it in at around .9 volts and need to know what this equates to. It seems like it could be a little snappier so I am thinking that this is richer than 12 to 1. Maybe it is just because it is a turbo that it isn't as snappy. I never tuned a turbo before. It does make the power though. It was running 8.00 in the 1/8 with the carb and that was pinging in high gear. It doesn't ping any more with the injection so it should be faster because I can crank the boost up to 15psi.

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Steve Arndt · Post by **Steve Arndt** » Thu May 24, 2001 8:39 am

I know what ratios work best on an aircooled engine.

.5 is 14.7:1 or very close.

You can not obtain ANY other ratios from ANY other voltages. You can only know lean and rich. That was my point, and the reason I explained WHY they designed the sensor to work this way. It is not a design fault, it is on purpose.
Steve

Steve Arndt · Post by **Steve Arndt** » Thu May 24, 2001 8:41 am

Keep it at .9 and you "should" be rich enough under boost to not melt it. Tuning with with a wide band O2 sensor on a dyno is the only way to extract max power.

Veepster · Post by **Veepster** » Thu May 24, 2001 1:48 pm

Steve you ae tight on the money!.....I have understood the same...the cat likes the swings from rich to lean to keep them working properly.....

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Peace.............BartG www.teamgodspeed.com

turbo6bar · Post by **turbo6bar** » Fri May 25, 2001 7:19 am

Chuck, with due respect, please study up on narrow band O2 sensors. If you are tuning the engine WOT with the O2 sensor, you may run into some serious issues. Parameters such as exhaust backpressure and EGT will affect the curve, and what you think is 12:1, may in fact be 9:1, or worse, 14:1. As Steve and Bart said, the O2 sensor has a wild curve. The OEM emissions-compliant ECU actually switches the mixture from lean to rich, which is easy with the narrow band O2 sensor, since it's voltages swing wildly away from stoich. If you are doing some serious tuning, I hope you are pulling plugs. That is a far better measure of your mixture. Of course, if you have access to a wide-band O2 setup, then you are doing a lot better (than narrow band, that is).

regards,
jay

Veepster · Post by **Veepster** » Fri May 25, 2001 9:17 am

so with all this talk about wide band, I am looking into purchasing one.......has anybody done any research on the prices and features of the ones available?.......any help would be appreciated!

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Peace.............BartG www.teamgodspeed.com

Chuck Schneider · Post by **Chuck Schneider** » Fri May 25, 2001 5:05 pm

Guys, Since I can get no answer on this subject I just got my CB air fuel gauge and o2 sensor and tuned the car to 12.5 to 1 on my gauge. I will put the bosch o2 sensor back in and see what voltage it is putting out. I think it is quite a large waste of money to spend 1000.00 dollars to tune a car when the same thing can be done for 50 bucks.
I have tuned quite a few cars with a narrow band o2 sensor with no problems at all. All you need to do is get it at 14.7 to 1 at idle and then 12.5 to 1 under hard acceleration and believe me I know that my guage is correct if you have the ratio at 13 to 1 you can definitly feel the difference in power.

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turbo6bar · Post by **turbo6bar** » Fri May 25, 2001 6:03 pm

<BLOCKQUOTE>quote:<HR>Originally posted by bruce:
Jay, that wide band O2 sensor for near $1000 is no good. You have to have an in-ground dynomometer and a 5 gas exhaust analyzer. Anything less is a waste of time. This should only cost a mere $15,000.
<HR></BLOCKQUOTE>

Bruce, is the above a fact or your opinion? I have heard absolutely nothing negative about the wide-band setups. Trying to compare an $800 M&W wide-band setup to a $10-20k Horiba is not fair.

Go to any Haltech forum or the DIY-EFI list, and you will find everyone does not agree with you.

regards,
jay

turbo6bar · Post by **turbo6bar** » Fri May 25, 2001 11:02 pm

<BLOCKQUOTE>quote:<HR>Originally posted by Veepster:
so with all this talk about wide band, I am looking into purchasing one.......has anybody done any research on the prices and features of the ones available?.......any help would be appreciated!
<HR></BLOCKQUOTE>

You have a handful of models from which to choose. There are two classes of wide-band O2 setups. One is based on the Bosch LSM-11 O2 sensor. It has decent response, and is indeed much better than the narrow-band sensor you find in virtually every OEM application. The second type of wide-band setup is built upon the NGK wide-band, which is considered superior to the Bosch LSM-11. The NGK is such a good unit, it is reported that you can actually see a misfire, and be able to distinguish the offending cylinder.

As far as available kits, Autronic, M&W, and a few other guys sell them. The M&W is the cheapest, and also uses the superior NGK sensor. The M&W is roughly $800US for the interface, sensor, and harness. You still need a notebook computer to interface. Various displays can be purchased to read out air/fuel ratios, but that adds another $100-1000 to the $800 price tag.

I am going to buy one in the near future. If anyone is interested in time-sharing or renting it, I'd be willing to discuss.

All the wide-band setups will give you readings within roughly .1 AFR. This is true accuracy, and not some haphazard guess, as with all the narrow-band kits.

jay