LeftySS

iTrader: (17)

Lets say you are running OLSD and have your VE tuned to produce the A/F ratio you are commanding in your PE table. Then you want to change the PE table to lean the mixture out, Will you then have to retune the VE or should you get the commanded A/F ratio?

jimmyblue

iTrader: (11)

You should still be good-to-go, the VE table ought
to care very little about fueling (though some minor
effect might come from scavenging / residual gas,
ditto timing, it should be "in the noise").

LeftySS

iTrader: (17)

Ha Ha. Now I am confused. I guess I need a little more education.
Just so there is no confusion I plan on staying in OLSD mode. Does what you say still apply? If yes then
how does the VE, OL table, and PE table work together? I know the OL, and PE
are dividers and multipliers of 14.7. So theoretically is the VE table telling the computer what
the air flow is for a 14.7:1 A/F ratio? So it can then calculate the commanded fuel by the multipliers and dividers?

So why do we set the commanded fuel to what we want and then tune the VE instead of setting the VE to what we want and
then tuning the OL and PE tables? I know a lot of guys will set their OL table to 13.0:1 and tune the VE to that. So how does
the computer change the fueling when the OL table is adjusted back to 14.7:1 or a multiplier of 1, when you don't adjust the VE
table for the change?

The reason I ask is because I have the car pretty well dialed in in OLSD. Part throttle and PE. I just want to be able to change the PE table to maybe lean it out a little more to see if I pick up some time, and not have to mess with retuning the VE.

Thanks for your insight.

69LT1Bird

iTrader: (1)

You tune the VE to stoich (via a wideband) and the PE is for commanding fueling above stoich for WOT. WOT is determined by the percentage of throttle or kPa that is preset by you.

If your VE table is deadnuts on you should be able to adjust the PE table (within reason) to whatever you want.

LeftySS

iTrader: (17)

What is that value in the VE table telling the computer? Is that the percentage of air that is filling the cylinder in relation to it's size? The volume of air in the cylinder?

69LT1Bird

iTrader: (1)

VE is an estimation of air in the cylinder determined my engine size and dynamics.

SS Enforcer

The way I see it is we do the data logging to determine the VE of the motor with mods so we can then get afr we command. Mine is OLSD as well and I get commanded fueling everywhere but don't use PE.
If the VE table is correct you should get whatever you command in PE mode to answer the OP's original question.

cheers

JonCR96Z

iTrader: (33)

All of the above.

VE is airflow. Once the PCM knows the amount of airflow into the engine at any given MAP/RPM value then it can add the correct amount of fuel to achieve any commanded AFR

LeftySS

iTrader: (17)

So the VE is the starting point for all fueling. So no matter what commanded A/F you are tuning the VE to, the numbers should end up being the same when you are through tuning?

JonCR96Z

iTrader: (33)

I don't like the way that you're saying it. You're not tuning the VE to a certain AFR, you're using the AFR error % to figure out what the VE is. Same for the MAF. They are just the airflow model, totally unrelated to fueling by themselves.

LeftySS

iTrader: (17)

Ok, I think I see what you are getting at, but why is it that when you change
the VE table the A/F ratio does change? Does the computer not use the VE values in some way to calculate fueling. The way I understand it, is you set the OL table and PE table to what A/F ratio you want then you adjust the VE until you start getting the wideband to match what you are commanding. So how is it not related to fueling in some way? Am I just totally off base here? Not trying to be argumentative just trying to understand what is going on.

Gh0st

iTrader: (3)

If you are in open loop and you modify the VE values, your air fuel is going to change accordingly to what you just screwed up or corrected.

69LT1Bird

iTrader: (1)

Plus its the air side of Air/Fuel ratio. That is why everyone says to make sure the injector tables and values are correct before you begin tuning. If the injector IFR, pulse widths, etc are correct you are adjusting the air side with the VE table(s).

69LT1Bird

iTrader: (1)

From Hp tuners help file:

VE Table: This table is used to determine air mass per cylinder in case of MAF failure and also to provide a base airflow value to check for MAF failure. It is also used to provide transient condition correction to the VCM main air mass calculations. Although it is not strictly a VE table in the traditional sense, it is displayed in % for convenience.

LeftySS

iTrader: (17)

So am I right with this logic? It doesn't matter if you decide to command 14.7 or 13.0 or whatever, when you are tuning VE.

The values you end up with in the VE Would be the same either way? That is if you get the % error down to the same amount for each.

JonCR96Z

iTrader: (33)

VE and MAF are just measuring airflow. The ideal way to tune it would be on a flow bench, but that's pretty much out of the question for anyone except the manufacture.

The PCM then uses the values set in those tables to calculate how much fuel is needed to reach the commanded AFR, but the tables themselves are just airflow.

The reason it changes the fuel when you mess with the VE or MAF tables is because the PCM thinks that there is a different volume of air. So it adds the amount of fuel it thinks it needs to get what it is commanded. Which will be the wrong amount unless the VE and MAF tables are correct.

LeftySS

iTrader: (17)

Thank you. That is what I was wanting to hear/see. I guess I was having a hard time communicating the question I had.

It is Airflow values which are used (in some formula) to HELP determine the fueling. But for these values to

be correct the Injectors have to be scaled correctly. So it doesn't matter what commanded A/F you use to arrive at these values, they should end up being the same?

Thanks for everyones input. Was just wanting to verify what I thought to be correct..

joecar

1. The PCM computes airmass from VE table (g*K/kPa).

2. The PCM looks up the AFR (richer of OL commanded fuel and/or PE tables) independently of airmass computed in 1 above.

3. From 1 and 2 the PCM computes fuelmass.

4. The PCM looks up the IFR table independently of fuelmass computed in 3 above.

5. From 3 and 4 the PCM computes injector pulse width.

LeftySS

iTrader: (17)

Now I am seeing how it all works together. I knew how to go about tuning the car as far as how to setup the scanner and what tables to adjust according to the wideband. Just wanted to know how the computer interprets all this and then determines the amount of fuel. So if no airflow characteristics of the engine change then VE can be left alone.

JonCR96Z

iTrader: (33)

Yeah. If you change your brand of lid or clean your air filter, VE is effected. Though probably not enough to worry about.