Thread: Lean burn tuning

GTPower... You are a bit off base here. What Kyne is saying is actually right.. closed loop will ALWAYS set lambda to 1, no matter what. The AFR value you set in the PCM is just telling the pcm what it takes to achieve a lambda of 1.

Considering this thread is about lean cruise, not make my car run on exotic fuels at 1 lambda using AFR numbers in the PCM.... you could trick your narrowband to look for a switch point of like 150mv to achieve some form of close loop lean cruise, although it would be a complete mess and probably wouldnt work.

Originally Posted by GTPpower

Unless I mis-typed something, I don't see where we disagree.



Whatever that table is set at, plus all active adders/mutipliers is what 1.00 Lambda is equal to.

What Kyne is saying, is that the trims will try to correct it back to 14.7:1, no matter what is commanded, which isn't true.

And that's why you misunderstand what lambda is. Lambda is just stoichometry for the fuel. Lambda 1.00 is 14.68 for pure gas or 450mv on the narrow band. So it will always get back to that. You can change the stoich to 16.00 and it will run at that until the fuel trims bring it back in line to stoich.

Originally Posted by GTPpower

No they won't. You can change commanded to whatever you want, and that is what the trims will shoot for.

So, that means:

Commanded=450mv=1.00 lambda.

450mv on a narrow band is stoichometry. That doesn't change even if you change the commanded. 450mv= 14.68 pure gas, 450mv=9.8 e85, 450mv=14.1 e10. It's not commanded, that's a number that depends on the fuel. Put a wideband on it, it may start out at commanded but will slowly go back to whatever your wideband is set up to show stoich. On mine it's 14.57 and the trims will slowly correct to that no matter what.

You have to throw AFR out the window though, that's just a number chemistry tells us is stoich for the fuel. The real number is lambda. The computer doesn't have a AFR sensor, there is no such thing on a car. It has a lambda sensor which determines when there is no limiting reagent in a stoichometry chemistry equation.

Commanded is not lambda 1.00, stoichometry (not rich or lean) is lambda 1.00. If you want an actual afr of 16.00 you have to shoot for a lambda of 1.088 on gas.