I’m trying to understand how the PCM uses the VE tables for my 98 TA.
There are several open threads in many forums about this topic, but I still don’t get it.

Here what I’ve find until now:
The LS1 PCM mainly uses the MAF signal, this works well at mid – high load and during constant operation.
The MAF is less precise at low load and during fast load changes. In those situations the PCM relates to the VE tables.
The main VE table is for normal operation, the secondary only if the MAF is disconnected (or not working properly).
The table to adjust is the main VE table.
To properly adjust the main VE table I first have to adjust the IFR table working in closed loop, then go in open loop and work with VE.
Open loop: either increasing the Closed Loop Enable Temperature to an impossible value, or disconnecting the MAF. If disconnecting the MAF first disable the SES light for P0102.
Also set the PE table to 0 (and drive at low – mid load!). After doing this (and always after changing the VE tables) reset the PCM.
Scan the O2 sensors at different loads and aim for 450 mV.

This is not my opinion, nor an explanation; it’s only what people write about the VE tables.

Is this the correct way to work?

Hope someone can help!

Stefano

 

VE stands for volumetric efficiency. Basically it means the amount of air that that is used for combustion at a given RPM/LOAD. Alot of people do not believe in VE tuning but Joe Overton has tuned using VE on LS1 cars and I even tuned my car using the VE tables and its an LT1 ( obd2)

From a personal opinion, unless you have a large cam and head work done I wouldnt mess with the VE. If you do not know what you are doing you can hurt your performance.

 

Not worthed for long tubes and FIPK?

 

(maf gms)/(rpm x 8 x cyl. vol.) = Volumetric Efficiency

If your maf is functioning correctly, the VE tables are not used. They are only used in speed density mode (i.e. maf is not functioning, or you have a 1993 or older fbody)

No need to mess with the v.e. tables, in fact, there is a very well known tuner that has a 'generic ve table' that he uses for almost ALL mild-mid cams on 94+ cars, just in case the maf stops working, it will still run a little better than if the stock ve table were to be used. So just keep that maf working and you don't need to touch that table.

 

Juiced LT1, I read here and there that the VE tables are used if the MAF goes bad AND also during fast load changes, this because the MAF can't react that fast.
I changed the main VE tables myself and I saw a difference in the LTFT, however: I don't think that changing the VE tabe is the only place to play when tuning.
Right now I lowered the IFR by 6% and reduced the MAF 5% from 1500 Hz to 2500 Hz, then linear to 0 until 4250 Hz.
All the cells are now between -1 and -2.
I just was thinking that adjusting the VE table I would give me a better response.

 

sorry your wrong the VE tables are used when the maf is fuctioning correctly.
go and put all your ve values at 30 and whatch what happens. you can find tune your blm to 128 very easily with the VE tables.

 

VE tables are used in MAF cars even when the MAF is working. Atleast I can vouch for it on my 97 OBD2 trans am. I do not want to turn this into a debate about VE is or is not used. I know for a FACT its used in my 97 TA. But maybe not for others, however.....Long Tubes and FIPK definatly does not warrant changing the VE tables. Even small cams dont usually benefit from VE table changes. But heads and moderate to large cams definatly can benefit from VE table changes (atleast OBD2 cars)...but again I am only speaking from experience.

 

In the obd2 and ls1 crowd the ve tables are used greatly.. i suggest you head to efilive.com and check out numerous threads about this.. they are explained in great detail... Whats more, they have a way to calc it almost correctly to fine tune it.

 

Thanks Highlander, efilive.com is a good source. Also hptuners.com.
All those informations are like puzzle! Some pieces are always missing. Apparently it also depends on the year of the PCM. Some old PCM uses the secondary, the newer the main VE table. But I still don't have the great picture.
I'm trying myself to change a region of the tables (main and sec) and see which table has the bigger effect. But no explicit result for now.

 

Not trying to beat a dead horse, but explain why the VE tables would be used in MAF mode? The VE of a system is a measure of the volume of space displaced by the cylinders for a given time against how much air actually passes through the maf. I don't see why you'd use the ve tables if you knew the rpm, vol of each cylinder, # of cyl, gms of air through the maf, and air temp (for density). That's what calculates the real time VE. It wouldn't make sense to use a table if you could get a REAL number.

 

Agh.. hptuners...

 

http://www.carcraft.com/techarticles/24549/

says MAF readings are exceptional at reading low-mid air flow, and they don't use the predefined ve-tables, they are only used in speed density mode, but what does carcraft know (and other PAID tuners for that matter)

 

So Iguess the 40 rwhp I gained when tuning my 383 with VE and TIMING tables only didnt really happen. And whats ever weirder is my AF ratio changed too !!!!

 

Just a short information: I lowered my secondary VE table by 30%, reset the PCM and made a long log: the LTFT are exactly the same as before.
I expected to see some cell going positive or at least chenge: just nothing.
Some people was able to change the LTFT messing with the secondary table, this is't the right way for my car (98 LS1).

 

If the ve tables are used in maf mode, what do they measure, or how are they used? Also, what does the pcm use if the MAF goes bad? How will it know how much air is coming in? It's got map, rpm, and air temp, but no maf readings...aka, speed density mode. Ever tuned a speed density car? They rely solely on the ve table.

If you take both of your o2's out of the bungs and let them sit outside, and you run your car for 5 minutes, your ltft's will go to 160, causing you to run PIG rich. Now lets say you get on the road, and punch it, with both ltft's at 160, do you suppose it'll kick into open loop and run fine at WOT? No. It's because the pcm DOES use the ltft's at WOT, and WOT is not OPEN LOOP. WOT simply locks the stft at 128 which locks the ltft's. And remember, when you flash you pcm, your stft and ltft blm's reset to 128, which can change a/f, which is why your car prolly changed a/f ratio's on the dyno.