Air/Fuel Ratio Question

[Mustangtk]

Hey guys,

Just installed a new unrestricted tune on my Steeda CAI, the air/fuel ratio under full throttle is now 11.6-11.9. That seems to be kinda a low number is this new tune safe to run? Regular acceleration the air/fuel is in the 14's

Thanks for the help

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[gtmiller1001]

Here's a good basic explanation of AFR: http://www.turbobygarrett.com/turbobygarrett/airfuel_ratio_tuning_rich_vs_lean

The lower the number the richer (more fuel/less air) the mix is. Motors don't pop because they are too rich, they fail because timing is too far advanced or the AFR is too lean (higher number). Too rich of an AFR will cause issues over time though...fouled plugs, injector issues, etc. For the record, I don't think your current AFR is anywhere near too RICH to actually cause issues, but you aren't maximizing potential power.

It also depends when you are taking the reading. On a naturally aspirated car (no supercharger, turbos or nitrous) you should be fine with a lambda of .85 at WOT. If you're using actual stoich of 14.7:1 then a .85 lambda would be an AFR of ~12.5. Basically, on an NA motor you should shoot for a lambda of .85 under WOT...that stays constant. Then you convert it to AFR depending on your type of fuel is. Pure gas (no ethanol), pump gas with some ethanol, E85, race gas...they all have different stoich points.

Since gasoline has up to 10% ethanol these days that old standard of 14.7:1 for stoichiometric AFR is actually slightly high. I think you can use something around 14.3 for current gas blends with up to 10% ethanol (someone correct me if wrong here). If that is what you use and you go for a lambda of .85 then .85 x 14.3 = 12.15:1 AFR at WOT.

Long story short, seems like you are still pretty rich (safe) an probably have more room left for power if they lean out the AFR a little more....assuming you are seeing this reading under WOT, the timing is within check (you'd have to log, no factory gauge for that) and you're not getting constant or excessive KR (again, you'd have to log for that).

EDIT: just saw you said under full throttle....I'd say you have room left for power if they lean it out a little...talk to your tuner.

 

[Timo5.0]

That write up was outstanding and spot on. Nicely done!

 

[Grimace427]

Here's a good basic explanation of AFR: http://www.turbobygarrett.com/turbobygarrett/airfuel_ratio_tuning_rich_vs_lean

The lower the number the richer (more fuel/less air) the mix is. Motors don't pop because they are too rich, they fail because timing is too far advanced or the AFR is too lean (higher number). Too rich of an AFR will cause issues over time though...fouled plugs, injector issues, etc. For the record, I don't think your current AFR is anywhere near too RICH to actually cause issues, but you aren't maximizing potential power.

It also depends when you are taking the reading. On a naturally aspirated car (no supercharger, turbos or nitrous) you should be fine with a lambda of .85 at WOT. If you're using actual stoich of 14.7:1 then a .85 lambda would be an AFR of ~12.5. Basically, on an NA motor you should shoot for a lambda of .85 under WOT...that stays constant. Then you convert it to AFR depending on your type of fuel is. Pure gas (no ethanol), pump gas with some ethanol, E85, race gas...they all have different stoich points.

Since gasoline has up to 10% ethanol these days that old standard of 14.7:1 for stoichiometric AFR is actually slightly high. I think you can use something around 14.3 for current gas blends with up to 10% ethanol (someone correct me if wrong here). If that is what you use and you go for a lambda of .85 then .85 x 14.3 = 12.15:1 AFR at WOT.

Long story short, seems like you are still pretty rich (safe) an probably have more room left for power if they lean out the AFR a little more....assuming you are seeing this reading under WOT, the timing is within check (you'd have to log, no factory gauge for that) and you're not getting constant or excessive KR (again, you'd have to log for that).

EDIT: just saw you said under full throttle....I'd say you have room left for power if they lean it out a little...talk to your tuner.

Ford uses 14.079 for their stoich calculations.

Otherwise, yes I agree the AFR readings are fine. Also should note OP I bet you were reading the AFR via the instrument cluster. If you really want to know if your tune is good you should datalog.

 

[cbrtrx]

That is normal fueling for these cars with those mods.

 

[gtmiller1001]

Ford uses 14.079 for their stoich calculations.

Otherwise, yes I agree the AFR readings are fine. Also should note OP I bet you were reading the AFR via the instrument cluster. If you really want to know if your tune is good you should datalog.

Didn't realize stoich was that low...if that's the case then yes, your AFR reading of just under 12 is fine. But I agree, if you want to get the most accurate reading you need to log.

 

[Dortzs550]

Question on the air/fuel ratio . My brother installed the blow off valve on his ecoboost now his air/fuel jumps up to 20 when driving . When at a stop sign the ratio is 14.5 . Any one alls having this issue ?


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[dgc333]

If you take your foot off the gas while the car is moving the ecu shuts off the fuel injectors and the air/fuel gauge will go to 20.

 

[Grimace427]

Question on the air/fuel ratio . My brother installed the blow off valve on his ecoboost now his air/fuel jumps up to 20 when driving . When at a stop sign the ratio is 14.5 . Any one alls having this issue ?

Not an issue, perfectly normal. Only time you should really focus on A/F is when WOT.

 

[Daytona Coupe]

Often times a tuner will add a little extra fuel as a little insurance against detonation. It doesn't hurt power much at all, and it helps lower combustion temps. It's not a problem.

 

[theredmeadow]

What's your air/fuel ratio at idle and cruise speeds? After a recent tune mine sits at 15.1-15.3 so I was wondering if this is a little high?

the car definitely feels faster, quicker acceleration, more pull. nothing sounds and feels different except more power. I'm just concerned bout this latest tune, I mean it's from a reputable/very experienced source and I'm using 91 octane.

 

[dgc333]

14.7:1 is stoichiometric, constantly at 15:1 or a little higher is on the lean side but not a problem for idle and cruising. Should go to less than 12:1 at WOT.

 

[theredmeadow]

14.7:1 is stoichiometric, constantly at 15:1 or a little higher is on the lean side but not a problem for idle and cruising. Should go to less than 12:1 at WOT.

thanks for the response. yeah at idle it'll bounce 15.1-15.3 and when light throttle it'll drop to the 14s but hang around 15.1

 

[NightmareMoon]

Sometimes at cruise a factory may tune on the lean side of stoich. (For low engine loads). I can't remember if that was for fuel economy or clean emissions or why though.

 

[theredmeadow]

here's an image of the datalog

https://drive.google.com/file/d/0BzCRz6Ixy-CMczZaNUNjZlNtbEE/view?usp=sharing

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