Questions to professionals

[odd boy]

I've got “why” questions on auto VE tuning tutorial: :help2::help2:

1. Why we change DFCO temperature to Enable? What about the rest of the list?

2. Why we change only "PE based on RPM" ? What about the rest of the PE calibrations?

3. Why we disable “long term fuel trim correction"?

4. Why we adjust the temp to 122 C under "closed loop temp"?

5. Why we disable catalytic converter protection?

6. Why we duplicate the high octane table to the low one?

7. Why we change all MAFs' frequency to 1?

8. How can I measure if I need to modify more or less?

Sorry for the long story :grin::grin:

[2002_z28_six_speed]

The AutoVE is not the whole story. You have to do more than what it says. The tutorial just gets you on the right track.

1. DFCO will throw off wide band tuning. You will realise it is coming on when you tune. Ensure it doesn't by raising the setting to where it could never come on.

2. It prevents the PCM from diverging from stoich so you can tune better. You can blank out more of it if you need to.

3. So the PCM doesn't change fueling. You can't read a tape measure if someone is moving it while you try to read it.

4. See 3. It prevents the PCM from trying to make fueling changes.

5. See 3 and 4

6. This stops the PCM from adjusting timing.

7. So the MAF won't have an effect on the VE. Tune the VE first.

[5.7ute]

Odd Boy welcome to the forum.
Just to add to 2002 z28's replies on a few points. (Though I am no professional)
1. DFCO when operating will cut fuel to the injectors.
1a. While DFCO is on the commanded fuel parameter will still be reading whichever is richer out of B3605 (B3647 if a custom os) & B3618 if enabled. Since the BEN equation is based between commanded & actual AFR the data you will get will be incorrect. This can be filtered out easy enough but as stated previously this is a guide for beginners & not the be and end all of autove tuning.
5. Cat protection is another of those fuelling changes that isnt reported by the commanded fuel parameter.
6. In a standard OS when the maf is failed to enter Speed Density (mafless) mode the low octane table is used by default.( For Safety as speed density is a back up mode) Since we are tuning the car we may as well tune it to its best conditions rather than the low octane table.
7. To enter Speed Density mode first the maf needs to fail. By setting the tables to 1 this will cause the maf to fail immediately upon start up & the fuelling calculations will be based from the VE table.
8. The amount certain cells need to be modified is calculated by the BEN factor. This equation which is your actual AFR measured by your wideband divided by the commanded AFR will give you a factor which then is paste & multiplied to the corresponding cell in the VE table.

[odd boy]

Thanks a lot:cheers: but what is BEN, and still I have some questions to your answer if you don't mind:

1a. I understood if DFCO is ON and PE is also ON the PCM will take the richer between B3605 and B3618. But if DFCO is off (didn't meet all activation criteria) it will go to PE if it is ON, otherwise it will select open loop mode.

[TAQuickness]

Welcome to the forum odd boy.

Lots of good questions. 5.7 and '02 have hit some good points for the specific questions.

The methodology is to create a steady-state PCM calibration to ease the tuning process.

DFCO, PE, CAT protection, and CL fuel trims are all fuel modifiers that will add or subtract fuel from the base fueling table. For instance, if you are trying to hit the low kPa region of your VE table and DFCO kicks in, your WB will report AFR's in the 19+ range. While this WB reading is correct, the data is not valid for producing a BEN (Base Effeciency Numerator [actual AFR/commanded AFR]) that is representative of the Volumetric Effeciency of the repective load point.

Likewise, we copy the high-octane spark table to the low because under normal operation the PCM will use a blend of both the High and Low tables. Spark timing has an affect on AFR readings, so for each given load point, we want to command the same spark value.

In the case of the MAF, the PCM uses yet another blending algorithm to blen VE and MAF table values. Since we are targeting the VE table as the base air flow table to tune, we have to disable the MAF to ensure our changes are applied accurately.

Of course, all of this is dependant on the IFR (injector flow rate) table being scaled correctly for the injectors you are using. Consider the IFR table as the one known constant in your tune that all other tuning changes are based on.

Please feel free to post up any other questions you may have. The more you know, the beter your tuning experience will be.

[joecar]

Welcome to the forum odd boy... :cheers:

Good comments above... :cheers:

When DFCO enables, it cuts fuel, and is not representative of the airmass obtained from the VE table.

The BEN is the correction factor that you apply to the VE table when tuning the VE table (or to the MAF table when tuning the MAF table)...

the BEN is the ratio of measured AFR to commanded AFR.

DFCO is not included in the commanded AFR; COTP may or may not be included in the commanded AFR, and if it is included it introduces transition errors;

PE is included, but if you're not careful it will introduce transition errors in the BEN as the PCM transitions in/out of PE.


During AutoVE you do not want the airmass to be calculated from the MAF, and you do not want closed loop trimming the fuelmass...
you want the airmass to come from the VE table and the fuelmass to be derived from the open loop commanded fuel table (B3605/B3647) and/or the PE table (B3618)...

this is so you can apply the BEN correction factor to the VE table without having other influences...

when the VE table is corrected, then you will see that the measured AFR equals the commanded AFR, which means you just set B3605/B3647/B3618 to produce the best peak TQ and peak HP.

It is important that the BEN represents steady state airflow conditions (good throttle operating technique and map filtering eliminate the transient conditions); a good BEN produces a good VE (and a good MAF when used for AutoMAF).

Cheers,
Joe
:cheers:

[odd boy]

Really all of you are too cooperative, this way I will be able to learn very quickly.

Thanks again.