Thread: Lean burn tuning

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.

Originally Posted by GTPpower

From what I've discovered, changing commanded will change O2's so that 450mv=commanded.

And, I drive everywhere with a wideband.

The function of an 02 is to find stoich. 14.68. You can't alter the tune and alter what 450mv is. 450mv=14.68 on pure gas period. It's how the o2 works and not something you can change.

Ok ill try to explain lambda a little better. If you have your stoich set to 14.7 and put e85 in there the car will run lean until the fuel trims makes up for it. It will slowly get to 9.8 afr (lambda 1.00) not stay at 14.7. Your wideband will start saying super lean at first and slowly go to 14.7 as the actual afr goes to 9.8. Unless you have an e85 setting on your wideband.

If you go the other way and put your stoich as 9.8 because you run e85 and then put gas in it it will be very rich but slowly go to 14.7 actual. In both cases your commanded will be the stoich value in the computer but will end up with actual stoich.

You also can't change the value that the narrowband Mv is, it's a sensor. So like a temp sensor a certain voltage = a certain number whether its lambda or it's temperature. You can recalibrating the computer to tell it that 400mv is stoich and it will think that number =lambda 1.00.

And lambda isn't commanded, you can command .75-.78 or whatever lambda in PE so that it achieves a fueling of 11.0-11.5ish. Commanded lambda isn't 1 then. That's why it's better to work in terms of lambda, 1.00 is always 1.00 and .78 is always .78 no matter the fuel.

Originally Posted by GTPpower

You are saying that it can't be done, but, I've done it. I put on thousands of miles testing it, and the trims didn't correct it. From my experience, trims will usually correct an AFR within a few minutes after switching to CL.

If I'm understanding you correctly, you are saying that the commanded CL AFR has absolutely no bearing on what the car will actually run once trims are accounted for.

Thats exactly right, if its working for you then something else is wrong on your car. Either your wideband is off or your o2s are bad. If your narrowbands are still switching at 450mv and your wideband says its lean then it's your wideband. If you aren't switching at 450mv then it's your o2s. Care to post a log?

Originally Posted by GTPpower

I have 2 widebands, and they are both within .1 AFR of each other, so I'm sure they are ok.

I've replaced the O2 on it once for general maintence, but it has always switched like it should.

I've been running the car in OL for about the past 3 years or so. So, I'm not sure that I will be able to find a scan anymore. I will check tonight if I get time and see if I can find one.


But, you are saying, that I can zero out (well, not zero...it won't let me), I can enter 8.0 in the stoich afr box, and it will make no difference?

Yeah, it won't run very well at first but once the trims kick in it will slowly correct it to 14.7 yes.

Originally Posted by GTPpower

From what I've discovered, changing commanded will change O2's so that 450mv=commanded.

And, I drive everywhere with a wideband.

nope. If you set it to 10:1, its going to still (try) to show 14.7 on the wideband no matter what fuel you have in it.