Thread: Lean burn tuning

I realize the point of the lean burn tune is to add a bunch of timing to the cruising tables and pull fuel from them. I've added timing but don't know how to pull fuel. Any help is appreciated.

Normally the you'd tune the MAF to add or remove fuel, but for doing it during cruise speeds I've never looked into it.

I've just added timing and never messed with fueling as I can get 30-32 freeway most of the time.

The lean cruise is tricky to accomplish on these. Do what cam said and you'll get excellent mileage. I had about 46° cruise timing. I believe it got closer to 50 at some points. Well over 30mpg all the time.

I run right around 35-38º of timing on the freeway, I've gone higher but it didnt do any better, so I kept it under 40.

Ok guys thanks for the input. I guess I have it setup pretty decent then. I'm running about 42-45* of timing.

Are you running close loop or open loop?

If open loop, you can do as said above.

If closed loop, you can change the commanded CL afr.


You will need to be careful, and possibly move your PE enable to a lower TPS% to prevent KR, because you will command this AFR until you hit PE.


The 04 GTO's have it super nice....there are tables in there for lean cruise that are only hit at certain throttle %'s after a certain amount of time.

as stated above adjust close loop Af. I normally run 14.9 and prob could run 15.0 you could adjust AE enrichment to help when you step on the gas to quench some KR if you see it or pull timing.

Originally Posted by Kyne

This thread is full of win. You can't just adjust CL afr, while it may adjust the computer for a little while the PCM doesn't care about AFR it cares about stoich on the narrowbands so it will slowly correct itself back to stoich or lambda that's what closed loop is. Open loop will work and on some cars so will tuning the o2 switch points. The 04 GTOs did sneak over here with lean cruise in the calibration just not activated, they are pretty slick.

As far as running it when cruising and how it is for pistons and valves, you could run your engine on air at low load and it wouldn't damage anything. Knock happens during high load driving. When you are in a lean burn mode you need to add a few degrees of timing to compensate for the burn rate.

You can adjust afr in CL. I've done it on a Grand Prix.

Lambda will obviously always be 1.00.

I've experimented with E85 by changing commanded CL afr to 9.8:1. Wideband said it was pretty close around there. And, I tested this method for a lot of miles.

Fuel trims will do whatever it takes to get lambda and commanded to match.


You will probably see inaccuracy from the sensor past a certain point, but since load is low for the most part, it won't really matter.

How do I know if I'm in cl or ol?

Originally Posted by Kyne

Facepalm. You obviously don't understand lambda.

You obviously don't understand how this PCM works.

Originally Posted by Kyne

You do realize all O2 sensors are actually lambda sensors not AFR sensors right? It senses lambda then multiplies it by an assumed stoichometry factory (14.68 for pure gas, 14.57 for indolene clear, 9.8 for e85) to come up with this imaginary AFR. So if your commanded lambda in your "lean burn tune" is 1 then it isn't lean burn. It has to command a lambda of >1.0 to be lean burn. The problem lies in your basic understanding of tuning. I was trying to help but I feel like I'm being fought the whole way.

For those who care the definition on closed loop is to keep the fuel ratio at stoich, so you cannot in any car with a narrow band have it lean burn and in closed loop. It has to be in open loop or if it has a wideband for a stock o2 (some newer cars) because the computer will correct it to stoich or lambda 1.00 which is 14.68 afr on pure gas.

And you can tell if you are in closed loop if you have fuel trims or your o2 readings are oscillating.

Ah, so you're saying my car did the impossible then.

Originally Posted by darkhorizon

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.

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.