Kryckter

All this based on TunerCat program

From what I have gathered about computer tuning, I have learned that the VE tables set the air fuel ratio. At least start the process of finding the targer air fuel ratios.
I know that the PE tables in both the % change tables, change the % of fuel from the VE table. Example would be a 10 number in the % change would add 10% more fuel at a certain RPM over the VE tables setting.
What I want to know, Is what formula is used to get the air fuel ratio from the VE table. How can I can get the computer's target air/fuel ratio from looking at the VE table.
What variables go in to account when figuring the target air/fuel from the VE table.
I know there is a lot of debate on VE tuning and I think that VE tuning is the only way to get a good tune.
The people that say NO to VE tuning and change all the numbers in the % change tables are really just chaging the numbers in the VE in a different way. Or actually giving it more fuel. Since I understand that the VE is only the air mixture.
Please shed some light on this.

Tommy'Z 6speed

I'm a little confused on this also.

I've just started playing with TC and from what I've gathered on this board, the PE tables are only active in open loop and/or WOT.
Therefore, the only way I see to tune closed loop is the VE tables.

I've used injector constant to move the whole curve rich or lean, but to alter the curve, I assume the VE table is the answer.

I also assume that, without a wideband O2, it will be trial and error based on BLM values at a given VE point.

Am I close?

Kryckter

Widband would be needed for accurate WOT tuning. The PE tables or % change tables are actually changing the target Air/Fuel by changing the VE tabls in percent. What I dont get is how the formula to calculate Air/Fuel can be accurate with the % change tables if any number is changed in the VE table. Can you only tune the % change numbers if you have stock VE tables. Cause in since if you change the Ve tables, Then all the percent change numbers would be wrong to the new VE tables and target air/fuel.

97Z-M6

no youve got it backwards the pe tables are not used in open loop.

ok now lets talk closed loop with pe tables the pe tables are the pre programed targeted a/f ratio you want to hit. now first: long as your blms are between 108 and 160 your car is running at 14.7 now if you go wot you may or may not be hitting your taget a/f ratio at wot (pe tables). now heres the catch. if your car is showing the blms below 128 it will hit the pe tables. now if the blms are higher than 128 (which shows a correction for what would be a lean condition) it will add the added fuel it was needing to keep you from running lean. so you will be running richer than its programed

Kryckter

But to go off of that..... The PE tables go off of the VE tables. I hear that any number in the % change vs. RPM is just the percent it will change the VE number. So how does one take the VE and get a target air/fuel, or what else is used in the PCM to find the target air/fuel.....VE table and what other variables?

97Z-M6

the MAF is used. it tells the pcm how much is coming so when you go wot the pcm refers to the amount of air entering the engine GPS grams per second. then trys to add the amount of fuel it needs to hit the target that you set in the pe tables.

now theres a big debate that says the VE tables are not used on a car with a MAF sensor. but i can tell you if you take a stock tune and fine out what rpm and map you run at 70 down the highway witht he cruise set, and make a note of the blms at that point. then go in and up the ve tables in that area and when you go back and set the cruise at 70 agian you will see the blms drop (to indicate a richer condition). becuase you are telling the pcm that the engine is more effiecent at that rpm and map so it adds fuel. the ve tables are not really nessasary to tune with, for the normal person. I WOULD LEAVE THEM ALONE.

the pe tables use the maf tables more than the ve tables.
dont worry about the ve tables at all. just use your pe tables.

now it is easier to to use the ve tables for getting your blms to 128 than it is using your MAF tables.

Kryckter

You say not to mess with the PE tables. But all the PE tables are changing are the VE tables. The only thing your doing in the PE tables is changing the VE table a certain percent at a certain RPM. So skip that part and tune the VE. VE tables are most certainly used on an F-body with or without a mass air. I just want to know the formula that the computer sees to make the car run with a VE table. What all does it take into consideration and what variables are used in conjuction with the VE table to make a target air fuel ratio?

Tommy'Z 6speed

97Z - I thought the PE table was used when "Power Enrichment" was needed, such as during acceleration. This is equivalent to the "pump shot" of a carburetor.

I thought the VE table set the A/F ratio during steady state RPM operation (cruise).

I'm looking to get my BLMs consistent in each cell. I would think I could use the VE table but you say I can use the PE table?

97Z-M6

the pe tables are for power enrichment mode. not cruising down the highway.

use the ve tables for getting your blms where you want them.

use pe tables for wot stuff.


now if your want the formula for the how the engine detmines fuel at wide open throtle "wot" then you might as well calculate the IAT sensor and the maf there are other sensors to contend with, in the great skeem of things. just worry about the pe tables for wide open throtle. and use the ve tables for getting your blms right.


and i have never seen the pe tables change the ve tables. i never seen my ve tables change when i chage the pe tables. my ve tables are stock.

are yall using tunercat or lt1 edit

Kryckter

When you change all your numbers in the % change tables...tunercats version of the PE. All you doing is changing the VE tables air fuel ratio, from what I understand. The number you put in the % change table, for example would be 10, that would be adding 10% fuel to the VE tables calculation. If you had a -2% in the % change table, it would be taking away 2% fuel at whatever spot you changed it at. So in turn, all your doing is modifying the VE table.

97Z-M6

its WOT AFR = 14.7 / (1 + %Change vs Cool/100 + %Change vs RPM/100)

Dan K

I think you might be trying to make things too difficult by figuring out how the ve table affects your pe table.
What I have always done (and I've found others to do the same) is to set the ve tables in the wot area to their maximum value, or 99.6.
That way you are taking any variance in the ve table out of the equation. It will make wot tuning much easier, as now all you have to worry about is the values in the pe vs temp and pe vs rpm tables. Looking at all of my pe vs rpm tables in my files, they are all filled with the same value and I get flat wot a/f curves.
The pe tables are there for a reason, take advantage of their simplicity and use them for what they were intended.

If you want to do anything with the ve tables in order to tune your part throttle..by all means feel free. IMHO, if your blm's are between 108 and 160 then the pcm is making any corrections that are needed to keep your 14.7:1 a/f ratio at part throttle. To me you're just wasting your time by trying to get those perfect 128 blms. If I'm between 118 and 138 in a majority of the cells I just leave well enough alone and turn my focus to something else.
The only time I've ever even messed with the ve tables was on a 93 that uses the ve tables solely for part throttle fueling, and for a large Joe Overton cammed car that I did last spring. Stock, hotcam, 230/236, and even 236/242 cars seem to work just fine on stock ve tables.

95Blackhawk

Ahhh the invevitable VE vs. MAF discussion.

VE, on 94 and up cars, was used as a safety net in case the MAF fails otherwise the VE tables are not looked at by the computer.

As for the computers, they at NO time know what the current AFR is. during non-PE mode, they only look at the cross-count from the O2's and adjust from there to get a BLM within a certain cell. In PE mode, they only add fuel to the last BLM seen in (more than likely) cell 15. Unless that cell was lean then it reverts to 128.

If you direct your thinking this way, I believe you will find it easier to understand tuning and get to the goal you want: a perfect AFR in PE mode.

Personally I don't like the term WOT, because the computer enables PE at times other than when our throttle is in the "wide open" position.

GL

Ben

97Z-M6

huh i have news for you they are used on a maf car when the maf IS working properly.

scan your car and record the blms the up your ve tbales by 10% and your blms will go up roughly 7 points.

everybody was saying they arent used so i decided to find out myself and are referenced.

Dan K

I did this on my car and it didn't change a thing.
I did it on a buddies car, and it did work.