shizon

iTrader: (1)

I use HPTuners so I'll direct my thinking in that regard. 2004 LS1

This is how I understand it....(for dummies or as simple as possible without things like ve multiplier, etc)

OK, so let's say I'm in SD. The VE table value holds the percentage of cylinder volume taken up by air. Basically, when we tune the VE table, we are correcting it's idea of how much air we got into the cylinder because we eased restrictions on the intake, MAF, valves, mfg tolerances, whatever else. More air is in the cylinder than the original parts could allow. So now the VCM calculates how much fuel to add to get the commanded afr (stoich in closed loop or commanded AFR/EQ in PE/Open Loop). The LTFT's and STFT's are there to correct the error in the VE table because the o2 sensors (say they report 14.2 A/F) reported that the VCM's calculation of how much fuel it would need to get to stoich was wrong. Thus you would see a +x% in STFT and a continual discrepency would cause a change in LTFT.

So now the next cycle around it looks up the VE table, calcs fuel, then adds the LTFT (assuming STFT is 0 now). Thus if we addthe LTFT directly to the VE table, the LTFT is 0 and the VE table is accurate based on our 02 readings (reading stoich).

But let's say we didn't change the VE table by adding LTFT. Thus LTFT is not 0 and the VE table value is stock.
Now we hammer it and get into open loop still in SD....

With the stock delay at 5500 rpm, we hit PE mode at 5500rpm, 100TPS. Engine load is 100kPa. Basically, since the o2 readings are now ignored, STFT's don't exist and the VCM starts with the VE Table value at 5500/100, calcs fuel for commanded afr (stoich/(final eq based on pe, iat,ect) and adds LTFT to correct for the VE inaccuracy.

My thinking is LTFT that is stored in RAM would not change in PE/Open Loop (no STFT's to change the LTFT's). Moreso, I would never have an LTFT at 5500rpm/100kPa cause I could not get there without more than 19 TPS (thus PE mode and no STFT's). So, how would you log your LTFT/STFT at that high of an rpm/load if they don't exist??? Or does it even matter...read on.

Thus, the only two ways to tune the VE in areas where we are in PE would be 1) the actual/commanded AFR wideband method of making actual match commanded by altering VE or 2)using the graph to make logical assumptions as to where the VE should be in relation to where it was going.

Does this make sense or am I way wrong on how this works. I know it's a bit over simplified, but think big picture.

Thanks guys

gameover

the short answer is you need a WBO2 sensor.

If you like to gamble you can try and work out the actual AFR from the O2 voltage readings using the old 890mv rule... personally i wouldn't recommend it.

ringram

Generally you disable PE so that the whole table is closed loop and use ltft to map all the points out. Its not ideal and not good to hit high map points like this, which is why using a wideband is strongly recommended. If you want to use ltft's and stft's you can, the info should be available on hpt forums.

bmfcamaro

iTrader: (1)

use the procedure in the help file in 2.0 . get a wideband. its worth it. 150 isnt bad compared to blown or underperformed engine.

SilverGoatGirl

iTrader: (2)

(just realized I'm on my gf's username)

shizon:
that's not quite what I was getting it. I understand that stuff.

The root of my question is if the VCM works the way I described, on a stock tune, how could you ever have a ltft when in PE.

ringram

You dont, there are only limited trim cells so the cell for wot is also stock active from 77map and 2400rpm from memory, that get used for PE AFAIK, though I only run open loop now...

SilverGoatGirl

iTrader: (2)

sweet, that's what i wanted to confirm
btw, still shizon