Best AFR value

[odd boy]

It was noticed that in any modified tuning file under {B3168} part, the AFR is between 11.95 and 13. The reason behind that is to be in the max energy of combustion zone.

My questions:

1. What basis does the tuner follows to select the optimum AFR value for max power?

2. Why changes are added only to B3168 (PE mode) not to B3605 (open loop mode) as well? For example, if I added a cam to X car, the introduced amount of air will be different so fuel should be different, regardless, on open loop mode or on PE mode, is that right?

[joecar]

That range of AFR is to obtain the best peak torque, but it also has side effects: for example the combustion chamber runs cooler (knock/damage is prevented).

1. the tuner runs on the dyno and changes the AFR to obtain the best peak torque and the best peak power; this can also be done at the track, but takes more time.

2. changes may be made to both tables, the last 2 or 3 columns of B3605 can be made as rich as B3618;

in open loop, if PE enables, the PCM selects the richer of B3605 and B3618;


B3605/B3618 are the command AFR... if you change cam, you want to change the VE table to reflect the actual airmass... then the PCM uses this airmass and the commanded AFR to calculate the fuelmass.

Cheers,
Joe

[odd boy]

one more question, do I have to fill the whole table of {B3605} and {B0101}. Still I can't realize how I get different MAP at the same RPM. And How I can create such condition?

[TAQuickness]

+ 1 on Joe's response.

It may not be possible to fill the whole table, so the real goal is to fill as much as you can. You will find the clever use of hills and gears will cover a good majority of the table.

[odd boy]

The picture is getting clearer. I live in sea level area, so I don't need the pressure at heights.

[Wasted Income]

No, he means that you use the hills to place the engine under load.

The engine will need more fuel and air to climb a hill at 2000 rpm than it will to decend the same hill at 2000 rpm, or to drive on level ground at 2000 rpm. It's not about altitude, it's about load.

You could also drag your brakes to put a load on the engine

[jfpilla]

In PE over 4000 RPMs the MAF controls fueling. If commanded AFR(B3618) does not match actual AFR then divide actual by desired AFR and adjust the MAF table at those frequencies by that %. ex: 12.00/13.00 =.923

With the MAF enabled the AFR from 4000rpms and over at WOT(PE) is commanded by B3618 only.

It was noticed that in any modified tuning file under {B3168} part, the AFR is between 11.95 and 13. The reason behind that is to be in the max energy of combustion zone.

My questions:

1. What basis does the tuner follows to select the optimum AFR value for max power?

2. Why changes are added only to B3168 (PE mode) not to B3605 (open loop mode) as well? For example, if I added a cam to X car, the introduced amount of air will be different so fuel should be different, regardless, on open loop mode or on PE mode, is that right?

[joecar]

jfpilla (Joe) is correct:

If you'r running with MAF then you correct the MAF table above 4000 rpm (or what B0120 says, this is the rpm threshold).
If you're running MAF-less then you correct the VE table.

Either way, you try to get the BEN factor equal to 1.00 (actual AFR == commanded AFR).

The commanded AFR comes from (regardless of MAF or MAF-less):
- CL: long/short term trimming to stoichiometric AFR [from O2 sensor feedback];
- OL: richer of OL AFR table (B3605) and PE table (B3618) [when PE enabled]

I'm always assuming that everyone has ditched their MAF...

[joecar]

You can't correct either of MAF or VE below 4000 rpm (B0120) with MAF enabled because the PCM uses a combination of the two.

When correcting the VE, you have to have the MAF disabled.

When correcting either of the MAF or VE, you have to be in OL otherwise the trims are correcting ahead of you.

[jfpilla]

If you don't have a WB you can dial in the MAF in CL using B5001 and LTFTs. You will need a WB or dyno tune to correct or at least check Actual AFR/Commanded.