Try altering the PE settings so PE comes in sooner. Then alter the PE commanded AFR's so that at "cruising" speeds, you run a "leaner " PE. For example, you might set PE AFR's to be 14:1 at 1000 RPM and slowly richen up to 12.4:1 at 2500 RPM. This way you will drop into a richer mixture when you load up the motor more for cruising, but still have plenty of fuel available for WOT runs.
Simon.
Hi Simon,
Good idea. I have reset all my settings. My LTFT are back to +/-0.5%, so i am calibrated on MAF and VE.
I have set my pe to come in at 60kpa and throttle at 40%. My PE is starting at 14.00 moving towards 12.4 at 2500RPM. if this works then i can play allittle more with the spark table.
regards
Mark
what about changing {B3671} by -5%
How is altering the Stoichiometric Ethanol blend value supposed to help here ?Originally Posted by tadmur
Simon.
if the car is flex fuel enabled {B0178}, shouldn't the ECU look up {b3671} to decide what is Stoich. and adjust fuel to get that reading from O2s?
Did I miss where Ethanol was mentioned? I thought the issue was just commanding additional fuel at altitude because the car ran better.
If you read the rest of the thread, the O2's are controlling the AFR's at the the correct stoichiometric level for the fuel being used. So trying to fool the ECM simply won't work as the O2's will pull the AFR's back to stoichiometric.
Simon.
i'm new to OEM computer and EFI... things are done a little different with stand alones..
but i get it... the ECU is using {b3671} to estimate (calculate) how much fuel to use but still trimming using O2 to lamda 1.. no matter what...
unless it is in PE or Open loop.... right??
Kind of, the ECM primarily looks the the O2 sensor feedback in CL. The crossover rich/lean (stoich) is abot .450V. Regardless what fuel is in the tank or what settings you make to B3671 the ECM will strive to switch the O2's around stoich.
If I remember correctly from my stoichiometry class while the A/F ratio changes with the fuel used; the NB O2 looks for 1.5% oxygen (upstream no AS) in the exhaust.
Last edited by VEGASROBBI; April 16th, 2010 at 03:10 AM.
Close.......
The ECM uses the existing fuel maps to calculate the required amount of fuel to add to the incoming air. The calculated amount of air, is then manipulated by the NB O2 readings to either make the mixture richer, or leaner than stoichiometric. The O2's will always give the same voltage output, no matter what fuel is used, as it looks for the oxygen left in the exhaust gas. So the NB O2 sensors will always read "Lambda" and not AFR.
So to control the fueling in CL, the ECM will look at what the NB O2's are reading, and add or remove fuel to drift the lambda reading back and forth from rich to lean. The average of the amount of correction needed to do this, is known as the Short Term Fuel Trims ( STFTs ). Changing any stoichiometric setting in the tune, only effects the base fueling levels, and not the NB O2 corrections. In CL, the O2 readings will force the average fueling back to stoichiometric and only the STFT's with change.
So to alter the amount of commanded fuel, you need to get past the O2 sensor correction. This can either be done by running full OL ( because we don't get a COS with semi OL in the E38 ), or you mess with the PE settings so yyou can retain CL for cruising / idle etc, but can command a different AFR when needed.
Simon.
So, would you say B3671 is the blend factor the ECM applies to modify the ethonal tables? Rather than name it AFR Commanded would it not be better to label it Blend Factor Applired and use Lambda as the units?
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