Desired Airflow Question, not your normal question

[Gelf VXR]

No, if I understand your original question correctly, the VE table is not a consideration. When you asked about the amount of air flow you need, I assumed your question was in reference to the "Desired Air Flow" table (B4307). If that's the case, that table has to do with the amount of air required for idle. The entries in this table typically have to be adjusted when a long duration camshaft is installed or any other modification that significantly alters idle air flow characteristics is done.

I never asked the question, but there is a long and short answer. When the MAF is not funtional how does the PCM know how much fuel to add.

Short answer, it uses the main VE Table.

Long answer, by looking at the VE Table, it will tell you it uses RPM sensor and MAP sensor, if you look at the funtion for VE it will tell you it references temperature and uses IAT sensor and ECT sensor, etc.

[Dale]

When the MAF is not funtional how does the PCM know how much fuel to add.

There never was a question on how does the pcm know how much fuel to add.

The question was about Desired Airflow.

[Gelf VXR]

But its relevant

[Dale]

The desired airflow affects the ve table. Yes.

I'm trying to figure out how the desired airflow is calculated when you do the refaig(sp?).

[joecar]

I forgot what the question was...?

Here it is...

What sensor(s) does the ecm read to determine how much airflow you need?

Maf? but what about when its in map only mode?

[Dale]

ok, tried the new maf out last night.

I dont feel that refaig is determined by the maf.

[dfe1]

I think you're getting cause and effect confused. The entries in the "Desired Air Flow" table tell the PCM how much air flow is desired to achieve the specified idle speed. The PCM then adjusts throttle opening or IAC position (depending on whether electronic or cable throttle). Desired air flow varies according to engine displacement, cam profile, throttle body diameter, desired idle speed, temperature and a number of other variables, so the entries in the table are established by the person doing the tuning, not the PCM. The purpose of monitoring RAFIG is to determine the difference between specified and actual air flow. Once this value is known, you can change the entries in the "Desired Air Flow" table so that the PCM has to do a minimum amount of correcting to achieve the desired idle speed.

[5.7ute]

The purpose of monitoring RAFIG is to determine the difference between specified and actual air flow. Once this value is known, you can change the entries in the "Desired Air Flow" table so that the PCM has to do a minimum amount of correcting to achieve the desired idle speed.

Rafig is not the difference between actual & desired airflow as I understand it. It is an airflow correction based on the difference between commanded & actual idle speed.
The amount of correction added or removed from the {B4307} desired airflow table is governed by a couple of other tables.
If the idle speed difference is less than {B4508} then the added airflow correction in {B4514} is used. The maximum short term correction is set in {B4521}.
An idle speed difference of more than {B4509} or when the AC is used will use {B4515} as the added airflow correction.
As I said earlier I could be wrong about this & the STIT & LTIT could use different tables that we cannot manipulate. i might have to have a look over a few old logs & see if I can verify this.

[dfe1]

RAFIG- Running Air Flow In Gear is the sum of long term and short term idle air correction. So in a sense, it is the difference between desired and actual air flow because if they were equal, there would be no correction. The PCM uses a variety of tables to determine the amount of air correction required, but the intent of using RAFIG data is to establish desired air flow data that minimizes the amount of correction required. As you alter desired air flow table data, RAFIG numbers will change to reflect those alterations. As an example, if RAFIG is positive and you increase the desired air flow numbers, the RAFIG values will become less positive or negative, depending on the amount you increased the desired air flow numbers.

I think all this makes sense, but as Joecar said, "I forgot what the original question was...?"

[stigmundfreud]

If you were sticking with a MAF system rather than scale the MAF table what would happen if you adjusted the VE table?