What to Tune First

[dfe1]

From all of my testing, I would have to disagree and say that once B0120 condition is met, MAF is used exclusively airflow calculation, transient condition or not.

Justin

I believe you're correct. I have an email from a GM engine control engineer that states MAF is used exclusively above what we know as the B0120 data point and that the system uses a combination of MAF and VE below that point, depending on whether the engine is in steady state or transient mode. The only time it uses VE exclusively is in the event of a MAF failure. The actual e-mail is on another computer-- I'll post it tomorrow.

For what it's worth, I've felt for a long time that below the B0120 point, the switch between VE table and MAF input operates along the lines of the high and low octane scalar-- it's never exclusively one or the other, but biased one way or the other depending on operating conditions. In this case, engine speed rate of change alters the bias. I don't know this for a fact, but all my experimenting points in that direction. After being the recipient of flack and other foreign matter about my cat-skinning procedure, and the rough edges it might leave, I put a vehicle that I had tuned using only changes to the VE table, into speed/density. The changes I see in long term fuel trims range between 0 and 12%, but there doesn't seem to be any consistency in the degree of change during steady state operation, as opposed to during throttle transitions. I need to do some more logging to see if any type of pattern exists.

[joecar]

Don't think of it as flack, think of it as a challenge or a debate...

[odd boy]

Guys,

Since I'm new to tuning world, you can ignore whatever I say !!!!

I think if I want to achieve the desired AFR value, either change the air [through {B0101} and/or {B5001}] or play with fuel [through {B4001}]. Why adjust both since it is ratio

[dfe1]

Don't think of it as flack, think of it as a challenge or a debate...

I have a wife and two daughters-- I know flack when I see it.

[jfpilla]

Guys,

Since I'm new to tuning world, you can ignore whatever I say !!!!

I think if I want to achieve the desired AFR value, either change the air [through {B0101}
xxxxB0101 would be used to change AFR in OL or SD.
and/or {B5001}]
xxxxB5001 is calibrated at WOT so that commanded AFR B3618 matches actual AFR.
or play with fuel [through {B4001}]
xxxxB4001 settings are either stock or calculated, IMO.
. Why adjust both since it is ratio

Does this help?

[joecar]

I have a wife and two daughters-- I know flack when I see it.

Man, you're outnumbered...

[odd boy]

xxxxB5001 is calibrated at WOT so that commanded AFR B3618 matches actual AFR.

Do you mean under WOT the PCM calculates the AFR through {B5001} and {B3618} only?

Would you tell me more about how the PCM works under WOT condition?

thanks a llllllllllllllllot

[jfpilla]

Do you mean under WOT the PCM calculates the AFR through {B5001} and {B3618} only?
xxxxx Some think VE's are involved, but I haven't noted any difference when VE's are changed.

Would you tell me more about how the PCM works under WOT condition?

thanks a llllllllllllllllot

I don't get the WOT condition question?

[joecar]

Is this what you're asking:

At WOT:
- the PCM calculates the airmass from the MAF (B5001),
- the PCM looks up the commanded AFR from PE (B3618),
- the PCM uses those two to calculate fuelmass,
- the PCM looks up the injector flow rate from IFR (B4001),
- the PCM uses those two to calculate the injector pulse width.

At WOT, airmass would come from B5001 since rpm is above B0120.
At WOT, PE would be enabled, and B3618 would be richer than B3605, so B3618 wins.
At WOT, MANVAC would be zero, so first cell of B4001 is the injector flow rate.

[jfpilla]

Joe,
Thanks.

oddboy?mmm
The last items I tune are spark and wot AFR.
That keeps everything else constant.
JP