fuel air ratio question

[Webbie13]

Before my car was tuned I noticed that the air/fuel ratio hovered around 14.5, now it is 14.0 on average. I am curious as to how low the air/fuel ratio can go before it will kill the cats.

The reason I asked is because less then 200 miles after tuning the car my engine light came on for P0420 "Catalyst system efficiency below threshold" Is this because the engine is running rich? or am I not running rich enough to cause a catalytic converter to die?

Thank you.

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[5.0yote]

Before my car was tuned I noticed that the air/fuel ratio hovered around 14.5, now it is 14.0 on average. I am curious as to how low the air/fuel ratio can go before it will kill the cats.

The reason I asked is because less then 200 miles after tuning the car my engine light came on for P0420 "Catalyst system efficiency below threshold" Is this because the engine is running rich? or am I not running rich enough to cause a catalytic converter to die?

Thank you.

14.5 to 14.0 is not "rich" enough to cause a cat code I am pretty sure. Usually its a bad O2 sensor, or an exhaust leak maybe. There can be a few things related but going 14.5 to 14.0 AFR is not the most probable reason.

 

[Juben]

14.08 is stoich for E10 (pump) gas. There's nothing to be concerned about at 14.0 as that's perfectly where it should be. The factory tuning is dynamic in that it can adjust itself for E0-E15 gas. If you saw a swing, i.e. it was higher or lower at some points, then it was just the tuning self adjusting for the amount of ethanol (E) in the fuel you're using.

Check to make sure the downstream (O2 below the cat) didn't come unplugged. A few hundred miles wouldn't kill the cat, even if it was running rich. If it's still plugged up, I'd clear the code and see if it comes back. If not, it was probably a fluke. If so, flash back to stock and see if it happens. If it doesn't on the stock tune, consult with your tuner. If it does on the stock tune, take it to the dealer. That code means a) the cat has taken a dump (doubtful) or b) something is wrong with the O2 sensor.

 

[jbailer]

When you say 14.5 or 14.1 regardless, you are talking about the car running under light to no load. The tuners aren't changing your target A/F there. Tuners tune A/F under load and most probably shoot for around 11.5:1.

3 primary readings you should see;
14:1 = light to no load
20:1 = fuel cut after you get going, take your foot completely off the gas, after a couple secs it will read this.
11.5 - 12.5:1 = A/F under full load. 11.5 for most tuners and I think stock is about 12.5:1.

A/F reading lag just a little as it takes a little time for what's happening to reach those sensors so don't expect a split second reading.

14.7:1 is stoich for regular gas with 0 ethanol. Then it adjusts downward as the ethanol content increases. Most gas stations use e10 now. It's possible you either switched gas stations or the gas station you've been going to just started using a e10 mixture.

 

[Webbie13]

When you say 14.5 or 14.1 regardless, you are talking about the car running under light to no load. The tuners aren't changing your target A/F there. Tuners tune A/F under load and most probably shoot for around 11.5:1.

3 primary readings you should see;
14:1 = light to no load
20:1 = fuel cut after you get going, take your foot completely off the gas, after a couple secs it will read this.
11.5 - 12.5:1 = A/F under full load. 11.5 for most tuners and I think stock is about 12.5:1.

A/F reading lag just a little as it takes a little time for what's happening to reach those sensors so don't expect a split second reading.

14.7:1 is stoich for regular gas with 0 ethanol. Then it adjusts downward as the ethanol content increases. Most gas stations use e10 now. It's possible you either switched gas stations or the gas station you've been going to just started using a e10 mixture.

So after a little more research I found that under full load my air fuel ratio is 10.8, with 14.0 cruise, and as you said 20 with closed throttle. Is 10.8 at full load a problem?

 

[5pointOh]

So after a little more research I found that under full load my air fuel ratio is 10.8, with 14.0 cruise, and as you said 20 with closed throttle. Is 10.8 at full load a problem?

That's quite rich TBH(depending on your mods). I'd advise your tuner and have them make some adjustments.

 

[stevnoof]

Are u using Cobb ots tunes?

 

[Webbie13]

I am using a Bama performance tune.

 

[stevnoof]

Alright. I was going to say I remember the Cobb tunes running rich when I tried them. I guess same for bama.

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