Commanded Lambda

[camguynj]

Is a Commanded Lambda > 1.0 commanding more fuel or more air?

[MagnumForceGB]

< 1.0 is more fuel than air, > 1.0 is less fuel than air

[camguynj]

Originally Posted by MagnumForceGB

< 1.0 is more fuel than air, > 1.0 is less fuel than air

Does that imply a Commanded Lambda of 1.10 is commanding less fuel because the engine is running rich?

[MagnumForceGB]

Yes, but unless it is in deceleration or power enrichment mode it should be 1.0.

[Rhino79]

In lambda, less than 1 is richer than stoich, and higher is leaner. In EQ ratio, higher than 1 is richer than stoich, and less than, is leaner.

[camguynj]

Originally Posted by MagnumForceGB

Yes, but unless it is in deceleration or power enrichment mode it should be 1.0.

Found out that Commanded Lambda is calculated by the ECM using fuel map info & various sensors to determine Short Term Fuel Trim.

So a Commanded Lambda >1will result in a -STFT (negative take fuel away) and Commanded Lambda < 1 will result in a (positive add fuel) STFT

[thahemp]

Trims don't have anything to do with commanded lambda. Trims are determined completely by the front O2 sensors in closed loop. If commanded lambda is anything other than 1.0, then narrowband fuel trims are useless.

[camguynj]

Originally Posted by thahemp

Trims don't have anything to do with commanded lambda. Trims are determined completely by the front O2 sensors in closed loop. If commanded lambda is anything other than 1.0, then narrowband fuel trims are useless.

Read the below link ...real good info.
http://info.efidynotuning.com/fuel101.htm

Note these highlights...

Lambse is a derivative of LAMBDA or the "AFR" (air/fuel ratio) the ecu is
demanding" .

STFT = Lambse
Short Term Fuel Trim is the lambse difference from stoich (1.000 - lambse) * 100 ,
It is the exact same representation of Lambse.
To put this into perspective, lets say at WOT we have a LAMBSE of 0.800
1.000 - 0.800 = 0.2 * 100 = 20 (STFT)
Now, lets say we have a negative STFT value of -18
1.000 - (-18 / 100) = 1.18 LAMBSE
as you can infer, a negative STFT means its removing fuel, so lambse will be greater than 1.000 (leaner)
a positive STFT means it is adding fuel, so lambse is less than 1.000 (richer)"

[thahemp]

Ok. I'm not sure what you're trying to get at here. STFT is still only useful if commanded lambda is 1.0.

[camguynj]

Originally Posted by thahemp

Ok. I'm not sure what you're trying to get at here. STFT is still only useful if commanded lambda is 1.0.

I'm saying that Commanded Lambda is the same as Lambse (which is dynamically calculated by the ECU and can be 1.0, <1.0 , or >1.0) to determine the STFT.

So when Commanded Lambda/Lambse is:
1.0 (STFT=0) no fuel change
<1.0 (STFT is +) add fuel
>1 .0 (STFT is -) remove fuel

[thahemp]

No that is not how it works.

Commanded lambda is not used to determine fuel trims. If STFTs are active, then commanded lambda is 1.0. Period.

Maybe you're confusing commanded lambda with actual lambda? They are two different things. STFT of +10% would imply that your actual lambda was 1.10 while your commanded lambda is 1.0. All the STFT is doing though is bringing actual lambda back to 1.0.

[camguynj]

Originally Posted by thahemp

No that is not how it works.

Commanded lambda is not used to determine fuel trims. If STFTs are active, then commanded lambda is 1.0. Period.

Maybe you're confusing commanded lambda with actual lambda? They are two different things. STFT of +10% would imply that your actual lambda was 1.10 while your commanded lambda is 1.0. All the STFT is doing though is bringing actual lambda back to 1.0.

I have a Dashlogic unit plugged into my OBD2 port. When it shows Commanded Lambda <1.0 it shows +STFT , when Commanded Lambda is >1.0 is shows -STFT

[thahemp]

Ok I had to go back and look at some logs to see when mine showed STFT values. Sometimes they don't make sense.. as in the values are there, but are not affecting fueling according to my wideband.

The ECM will command a richer lambda on startup and actual closed loop is on a 10 second delay when startup coolant temp is between 40* and 241*. Once that 10 seconds passes commanded lambda ramps up to 1.000 and fueling swings with the O2 sensor voltages as expected. Driving around I never see an EQ ratio other than 1.0 unless I go into power enrichment.

When do you see commanded lambda at values other than 1.0?

[camguynj]

Originally Posted by thahemp

Ok I had to go back and look at some logs to see when mine showed STFT values. Sometimes they don't make sense.. as in the values are there, but are not affecting fueling according to my wideband.

The ECM will command a richer lambda on startup and actual closed loop is on a 10 second delay when startup coolant temp is between 40* and 241*. Once that 10 seconds passes commanded lambda ramps up to 1.000 and fueling swings with the O2 sensor voltages as expected. Driving around I never see an EQ ratio other than 1.0 unless I go into power enrichment.

When do you see commanded lambda at values other than 1.0?

Always see Commanded lambda <1.0 at cold start up (.96 -.99) along with ST & LT fuel trims, very infrequently see Commanded lambda 1.1 while driving ...as these are displayed on the DIC its easy to view at startup, not so much while driving. Normally while driving I have the display set to oil temp, engine temp & gear ... mines a manual so it comes in handy at times. All good info in this tread. Thanks for your interest and posts.