Air Fuel Ratio

[gandulf2003]

hello everybody

i need some one to explane the AFR to me , coz i searched and foud that the 17 is lean and the 10 is rich!!

i have afr
14.7 cruse + idle
11.6 full throtle

and when my headers break down the AFR goes up to 18 and after that give me error!!!!

can anybody explan what happened to me !!!

and what mods do i have all in the signature

[jetmech]

AFR is simply your ratio of Air to Fuel NOT Fuel to Air. The number displayed on your wideband is the mass of Air to Fuel. 14.7 AFR means that the mass of air is 14.7 times the mass of fuel. Consequently the lower that number, the LESS air in the mixture which yields a rich AFR. And similarly, the higher that number is, the MORE air you have in the mixture which yields a lean mixture. As a rule of thumb, 14.7 (stoich AFR) is the optimum AFR while cruising so you're good to go there. When people say rich and lean, it is always in reference to a certain AFR.

As for full throttle, that number all depends on how much power/torque you want to squeeze out of it. 11.6 sounds fine tho. The richer you go, the safer it is and less power/torque you'll make. The leaner you go, the more power/torque you'll make. However, the leaner you go, the higher the chance you have of detonation. Again this is speaking in terms of full throttle.

When you say "headers breaking down" do you mean to say that your engine is winding down? If so, your wideband will go VERY lean, which is normal - mine does the same thing. Besides, the engine is not under any real load at that point


Overall, your AFR's look fine IMO

[gandulf2003]

thanks for the quick respond, about the headers it was like after the header will be to the atmosphere directlly

thanks again

[jetmech]

Still don't follow you but no matter what you do with your headers, your AFR will go very lean after your foot is off the gas pedal (off the brake too) for a few seconds - especially at higher speeds

And I'm glad I could help!

[pl4yboy]

Also depends on NA, Nitrous, or Boost.

[farmtruc]

Maybe he's referring to decel, like you said.
If so, that is called Decel Fuel Cutoff. The engine doesn't need to be rich during decel.
There is a setting to turn this off, but there is no need in your case.

[jetmech]

Maybe he's referring to decel, like you said.
If so, that is called Decel Fuel Cutoff. The engine doesn't need to be rich during decel.
There is a setting to turn this off, but there is no need in your case.

Yes, Decel is what I was referring to - just couldn't think of the name of it

[George C]

Also to rich will cause detnotation

AFR is simply your ratio of Air to Fuel NOT Fuel to Air. The number displayed on your wideband is the mass of Air to Fuel. 14.7 AFR means that the mass of air is 14.7 times the mass of fuel. Consequently the lower that number, the LESS air in the mixture which yields a rich AFR. And similarly, the higher that number is, the MORE air you have in the mixture which yields a lean m ixture. As a rule of thumb, 14.7 (stoich AFR) is the optimum AFR while cruising so you're good to go there. When people say rich and lean, it is always in reference to a certain AFR.

As for full throttle, that number all depends on how much power/torque you want to squeeze out of it. 11.6 sounds fine tho. The richer you go, the safer it is and less power/torque you'll make. The leaner you go, the more power/torque you'll make. However, the leaner you go, the higher the chance you have of detonation. Again this is speaking in terms of full throttle.

When you say "headers breaking down" do you mean to say that your engine is winding down? If so, your wideband will go VERY lean, which is normal - mine does the same thing. Besides, the engine is not under any real load at that point


Overall, your AFR's look fine IMO

[jetmech]

Really, how so?? About how rich will encourage detonation? I've never heard of this, then again I guess you learn something new everyday....

[farmtruc]

IMO it's not a big deal if it's too rich. When the a/f ratio is too rich, the truck will bog and not feel strong.
Even a 10.5 or 10.2 a/f ratio (at least on my truck and avalanche) still feels pretty decent.
If the a/f ratio is in the 9.0 area, the truck just don't run, so it's obvious that there is an issue, so detonation isn't a concern for me when running rich.
I've never had detonation occur when a vehicle runs too rich, cause 10.5 still isn't too rich, just my opinion.

I've heard others say this, that a rich condition will cause KR, but I haven't experienced it, but I'd like to hear about it.