LNF Commanded Lambda - a slow drift down from 1.00

[npaz]

I noticed today that my Commanded Lambda seems to have drifted down over time and different tunes. Currently it's at .95 at idle and .89 at light load and/or highway cruising.

Isn't it supposed to be at 1.00 on closed loop all the time? I thought that this was programmed into the ECU and not adjustable?

I'm nowhere near WOT or high enough load to be influenced by the PE table. Looking back at some old logs and tunes, it looks like it stared out at 1.00 then drifted down to .95 and now is at .89 much of the time. Adding a new tune doesn't appear to change this. Long term fuel trims are at zero.

Any thoughts?

Thanks!

[ECaulk]

If it's shortly after flashing a tune, the ecu is going through tests.

[npaz]

Thanks for the reply ECaulk. How long is shortly? Last flash 4 days and 4 test drives at 20 to 30 miles each. Sitting at .89 now. I would think a new flash would either reset the base commanded lambda back to 1.00, or do nothing.

To update the above. I've looked back at a bunch of logs with slightly different tunes now. I'm between .89 and .95 on all of them. Haven't been at 1.00 for a while now. Idle is steady on all at .95

Isn't base lambda commanded always supposed to be 1.00 on the LNF? Isn't it coded into the ECU? I've never read or found a way to change the lambda settings other than the PE table.

[T-Man]

Post a screenshot of your PE table

[npaz]

Here you go. I started out with a basic tune from Dave at Autowerks. He changed this a few times making it richer (.84) than this one at the high end. COT is off, so I think he was just trying to keep the cat cooler WOT. I am currently running this one though which is a bit leaner:

PE-Table.jpg

[cobaltssoverbooster]

leave the 60 column as 1.0 you dont need pe down there.

as long as COT is all 1.0 then you should only see commanded dips when running cat tests which happen very quickly few seconds at the most

[npaz]

Hey CSSOB. Will changing that column to 1.0 raise the light load / low rpm lambda back up to 1.00? Does the ECU reference the PE Table at 0%-50%? In other words, whatever the 60% column is set at is used for the percentages lower than that? Thanks!

[cobaltssoverbooster]

The ECU is smart as hell. If a table axis is exceeded either by going lower than the axis labels or higher than the axis labels, it has the ability to interpolate off axis values based on the last available cell.
Is it guaranteed, no. Is it possible, highly.

[npaz]

Thanks CSSOB. I flashed a tune with the 60% column at 1.00. Bam! Commanded lambda is now sitting there at 1.00 on two test drives, so that column must be referenced by the ECU in some way. Sweet!

[cobaltssoverbooster]

Sweet!

[T-Man]

I'd put the 80 column back to 1 as well. The pedal percentage header isn't absolute as the ECU will average commanded vs actual

[ECaulk]

I'd put the 80 column back to 1 as well. The pedal percentage header isn't absolute as the ECU will average commanded vs actual

I had the 80 column at 1 and then gave it a little gas in 5th (just accelerating to speed up, like quarter throttle it's 5th gear so not beating on it) and the boost pop'd to 15lbs and command lamdba of 1.00, so I usually run that column above 3500 at 0.95 just to prevent bad things from happening.

[npaz]

Thanks for all the advice! I ditched the old PE table and made a progressive one, keeping the 60% column all 1.00 and going a little richer as the table goes higher load and RPM. I'll see how it goes. I've got COT disabled, but am running a high flow cat.

I find it pretty interesting that the 60% column appears to be used as a reference by the ECU at all RPMs and loads from 0-60% (at less than WOT). Not sure what happens over 60% at less than WOT because my old PE table had the same lambda values straight across at 60,80,90,100. However, on my logs commanded lambda appeared to exactly match whatever value is set in the 60% column/RPM row at less than WOT. (Feel free to test and confirm or not).

I've never read that anywhere on the forum. I always assumed the ECU was hard coded on closed loop at 1.00 lambda and PE Lambda table was only referenced at WOT.

Being able to control this might be helpful to someone wanting to go leaner or richer than 1.00 lambda at a given RPM range or everywhere.

[MikeM173]

It?s not just for WOT. I mentioned it somewhere in some post I made at some point lol. You can?t change the values (60%-100%). You can change them in the tune, but it won?t actually change it on the car like some other tables will. That?s why I keep everything low power below 3000rpm, and then it starts increasing then as well. That applies with my lambda as well. I make some changes depending on what the car is being used for, but most people want a highway monster, with some track time (my experience). I also use .99 lambda instead of 1.0 because I?ve had some issues on cars when using 1.0, and when I used .99 I got 1.0. It just depends though.

[npaz]

If anyone is interested, I came across this old post from Iam Broke. He was discussing using the PE table to set up a lean cruise, but uses a term which I think best describes the PE table 60% column - "60% and less". That column seems to determine Lambda Commanded from 0-60%, but as he points out won't go above 1.0

Term and I both tried to raise the Lambda in the 60% and less column for the PE Lambda table to 1.05 and it wouldn't command anything higher than 1.0 If you change it to say .97, it commands .97 in cruise just fine