Help with a/f ratio logging and xcal2q

J

justinschmidt1

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Jun 15, 2005

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Mar 8, 2007

#1

• Mar 8, 2007

• #1

I logged my a/f ratio with my xcal2...from what ive heard it reads like 1.0 is normal and i think it was anything over is lean anything under is rich..so if it reads 1.10 it is .10 lean so it adds fuel right?..or is it reverse...I was messing around with it seeing how it worked and it went from 1.0 to about .75 when I was accelerating full throttle in first...at like 5500 or so it went to the .75 or .8 or so...what does this mean?

 

Give Me TP

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Jun 17, 2004

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Republic of Texas

Mar 8, 2007

#2

• Mar 8, 2007

• #2

It's reading voltage from your stock O2 sensors rather than a A/F ratio. To obtain useful A/F ratio numbers, you must datalog via a stand alone wideband O2 monitoring system rather than reading output from your stock O2 sensors via your vehicle's ECU. There is no way that I know to directly convert voltage readings to A/F ratio.

 

Don 95Vert

Founding Member

Oct 1, 1999

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Delaware, OH

Mar 8, 2007

#3

• Mar 8, 2007

• #3

The short term trims use the stock 02 senors for adat. If they are reading 1.1, then the processor is adding 10% fuel and 10% needs to be pulled. At WOT the STFTs reflect the commanded fuel from the base fuel table in lambda - so if you are seeing a STFT at WOT of 0.75, then the commanded fuel in the tune is 10.98 - which is really way too rich.

 

Give Me TP

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Jun 17, 2004

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Republic of Texas

Mar 8, 2007

#4

• Mar 8, 2007

• #4

Does stoich of 14.7 then roughly translate to 1.0?

 

the98stang

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Aug 12, 2005

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Clovis, CA

Mar 8, 2007

#5

• Mar 8, 2007

• #5

Give Me TP said:

Does stoich of 14.7 then roughly translate to 1.0?

Click to expand...

Yes but that's still too lean IMO

 

J

justinschmidt1

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Jun 15, 2005

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Mar 8, 2007

#6

• Mar 8, 2007

• #6

and the way to fix this is get a custom dyno tune right?...Ill be installing a pi intake soon...I plan on getting a dynotune after that.

 

fastfive_ogt

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Jan 31, 2006

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Wisconsin

Mar 8, 2007

#7

• Mar 8, 2007

• #7

well well my well knowledged friend don. This stft's you are talking about do not mean exact a/f ratios. Like Give me said the only way to read true a/f ratio is with a wide band. stft's do not take into account for worn or old parts etc... The table you are talking about is a base table also which is only used in open loop. once closed loop then pcm uses other factors to keep a/f at stoich 14.7 or to be precise a little above and a little below. Your method though would work closely but not the best way to tune a car. Dyno with a sniffer or wide band is best.