Why am I getting AFR spark correction when lean cruise is disabled?

[cobaltssoverbooster]

true they aren't gunning for me but i have been corrected here and thats a good thing for the OP, all readers, and for me because its something i can refer to again later.
i got stretched a little thin on this one and made a statement based on another platform that turned out to behave differently. If i had access to this platform like i used to then i would be testing things i have recently questioned myself but posted a comment on anyways using logical reason to try and back up my statement. Ive been wrong three times this week so not really as much help lately. i did try though.


i changed my previous posts to reflect the correct information here.

[Jon S.]

... they aren't gunning for me ...

No sir - not at all.

The original purpose of social media was to share accurate information and different points of view. This has unfortunately morphed into (some) people feeling free to commit verbal attacks and harassment. Back in the day, you would have been rewarded with a slap in the head, for such breaches of social decorum.

Our modern world is better in some ways, while far worse in other ways.

Helping another person is supposed to be an altruistic endeavour. I don’t consistently have the time to participate in this forum, and often go months between bursts of posts. I applaud anyone who consistently helps out.

[Jason B]

It still makes no sense to me. I was logging Lambda and it went to .85, on the chart I posted .85 is all zeros. yet it added 4 degrees of AFR Advance.

[Ben C]

That's because the table isn't lambda, it's equivelance ratio. The issue with tuning factory computers is the weird way they do things.

To explain it may be easier to think of afr.
so 0.85 lambda is approx 12.5:1
14.7:1 being stoichiometric.
that table is referencing 14.7:1.17 approx. So the 1.17 is the x axis on the table. Which is the same ratio, Pretty special.....

Maybe that's more confusing. You just need to divixe 1 by top number to see it. 1/1.17=. 85
remember gm did it for some reason that made sense to them, not for us!

[MikeOD]

Why am I getting AFR spark correction at WOT when lean cruise is disabled? HPTuners help file says that this table is only active if lean cruise mode is enabled. I suppose there's a mislabeled table somewhere?
In editor it's labeled AFR spark advance correction. In the scanner it's labeled AFR advance.
2002 5.3 silverado

Lean cruise or not, with commanded AFR changes, it uses this table.

So everything that HPTuners has written about the AFR spark correction table is wrong? Like in Editor itself? in the help files? All of that is misinformation?

Or is there some other table that I can't find thats adding spark at WOT?

Zero out the table, you'll see the spark correction go away.

The description is not correct then right?
Attachment 82984

Again, try zeroing out the table.

What do the top row of numbers represent on this table?

I'm getting 4 degrees AFR advance and nothing I calculate out is even close to these numbers.

Attachment 82985

They represent EQ ratio, which is the inverse of lambda. So if you're targeting 0.85 lambda, then 1/0.85 = 1.176, which is right between where your table has 3's and 5's, so the 4 degrees you're seeing makes sense.

I'm guessing the GM engineers put the numbers there. It's the stock tune for a 2002 silverado. Wasn't me, ain't that some shit....

They do it because they use PE delay and slow enrichment rate on the trucks, I think for fuel economy.

It still makes no sense to me. I was logging Lambda and it went to .85, on the chart I posted .85 is all zeros. yet it added 4 degrees of AFR Advance.

As I said above, you're thinking in lambda, but these tables in these computers think in inverse of lambda.

The reason the trucks have this table setup like this is because of PE delay and enrichment rate.

If you're driving a truck with a stock tune, and you put your foot down, it will start the PE delay timer. The throttle is open, the engine is pulling in air, but they're delaying how much fuel it gets, so if you immediately went to your full advance, it would knock. As the fuel ramps in from the delay and the enrichment rate, this table ramps spark in as well.

I think they do it on trucks because going up and down hills, especially with weight in the bed or a trailer behind them they burn less fuel this way. If you disable the PE delay, and set the enrichment rate the same as a car, so the fuel is commanded right away, it'll still add the advance from this table, it'll just add it right away. It's also why the main timing tables in the trucks usually look so conservative at higher airflow. If you want to simplify tuning the truck, especially if you're not going to actually use it as a truck (for example my 2005 has an 84mm turbo, no trailer hitch, and will probably never have more than 50 or 100 pounds in the bed again), you can zero this table, turn off the PE delay, and add timing in the main advance table instead.

[Jon S.]

... I was logging Lambda ...

Hi Jason,

With the P01 PCM log GM Equivalence Ratio, rather than SAE Lambda - it will make things easier to interrelate.

[Jason B]

Hi Jason,

With the P01 PCM log GM Equivalence Ratio, rather than SAE Lambda - it will make things easier to interrelate.

I don't see those descriptions.
Anyway I just zero'd the table out. I have two LS1 camaros and this silverado PCM is in an s10 with a 5.3 swap, so it's not going to be used like a heavy truck much.

Thanks everyone for the help.

Attachment 83058

[Jason B]

you put your foot down, it will start the PE delay timer. The throttle is open, the engine is pulling in air, but they're delaying how much fuel it gets, so if you immediately went to your full advance, it would knock. As the fuel ramps in from the delay and the enrichment rate, this table ramps spark in as well.

Makes sense. When the truck gets heat soaked and I go WOT it'll get (usually) 2 to 3 degrees KR. Ironically the same thats being added by this table. And I have the PE all set up like a car. I think I found the source of the KR.