slow2000z28

my ltft are at 16+ while at idle and also at low map pressure 35 and under. above 35kpa the ltft are 4. i tried retuning the car adding fuel to bring down the ltft but no matter how much fuel i add or even subtract th numbers remain the same. has any one run into this problem before? by the way, the car is in speed density mode.

Z'mnypit

iTrader: (58)

When adjusted the VE table you do have the MAF turned off right? Have you tried scaling the MAF table?

98redorangeta

iTrader: (10)

On 98-00 make sure your using the secondary ve table in sd mode. Also make sure you are resetting your fuel trims.

Sean Collins

How big is the Camshaft Duration lift LSA ICL ?

slow2000z28

im running in sd mode so my Maf isnt hooked up, therefore the Maf table isnt an issue. i have a stock cam. havent tried to reset fuel trims yet, actually was afraid 2. not sure what happens when i hit reset. i dont have awideband yet so i am trying to do this w/ stock narrowband 02s. if anyone can tell me what will happen if i reset the ltfts that would be great.

brad8266

iTrader: (23)

Make sure you are tuning the seconday VE table. When the MAF is unplugged the PCM runs on the secondary table. If you have been tuning the primary table then you are really making no changes in SD.

Purrvert

[QUOTE= if anyone can tell me what will happen if i reset the ltfts that would be great.[/QUOTE]

Long term fuel trims are learned from STFT. They stay in memory for a baseline fuel correction, supplemented by STFT. If you erase/reset LTFT, STFT will take over and over a period of 50 miles will relearn LTFT. Basically by resetting LTFT you will speed up the tuning process when you alter your VE table.

Sean Collins

Why are you doing this ??? Put the MAF back on. The MAF has nothing to do with closed vs open loop operation aside from the fact that it puts the ECM in defualt mode. Yes it will add a bunch of fuel trim in defualt mode. This is why your ltft is so high. There is no HP to be gained without the MAF and there are Factory MAF's that will support 500rwhp Naturually aspirated with near zero Pressure drop. the stock Intake Manifolds don't outflow the MAF if we are talking the late model 5pin. All your doing is breaking the operating system software in the PCM. It was never intended to run in SD mode unless there was a fualt. The VE tables are for Dyna Air or Accel enrichment and MAF error checking to deal with transient state load changes.The Back up VE table is the defualt mode table however. The Only GM box ever made to run SD with MAF or MAP was the early lt1 stuff. You can reset the ltft without cuasing to much trouble but agian the OS is broken without that MAF input.

Some people have modified the OS to run Sd but I have not seen the effectiveness of doing this as there are alot of Things in the OS that are dependent on the MAF.Secodnly there are large enough MAFS out there to cover the biggest NA motors i have seen. by the time your making 600hp NA then your into a whole new territory where the stock PCM is really a broken crutch.

Flame Suit On

Purrvert

SD mode is primarily used for VE table tuning, but some folks like it and leave it. Tuning objective is to get your fuel trims in the slightly negative area, then when you enter PE mode no extra fuel ie: LTFT from last table you were in before entering PE, will be added to the PE tables, making for unstable PE mode. Folks tune the VE and then optionally tune the MAF.

Sean Collins

Not really going to work since the VE table vaules are patially derived from the MAF input. You just have to log the car intensively and adjust the VE table based on feel, sound and aFR data. Yes the widebadn will be a touch bit behind but you can mentally match it up easily enough. big lean dip with TPS change and MAP increase.

the logic loop is something like this roughy.

Montior TPS,
TPS change,

Calcilate Delta equal to or greater than last TPS or fix TPS change ovr time setup for MAF estimation.

If greater grab last known MAF value ,Look Up VE Muodifier MAP vs RPM table apply Modifier to Last and Current MAf reading Sum all 3 then divide by 3 use average.

Air per cylinder Calc based on engine size then final PW based on simultaeneous injector grs/sec vs Vac.

there is alot more conditioning going on but thats the heart of the dyna air calc.thats why you have to have the MAF to do VE table tunning. without it your not going to get close enough.

Purrvert

Interesting. VE tables are a fixed item, how does the MAF influence?

Sean Collins

They are not fixed in dynamic air management mode.The calculation for dyna air is fiarly long actually.The code treats the VE tables as a conditioner when the MAF is in play on the vehicle. Thats why the standard VE tables don't work when you unplug it and it goes to the back up VE tables instead. The VE table is a conditioner and is used to Avg airflow for transient throttle. Its influence is averaged across 3 MAF readings. This was done due to surge volumes in the plenum and air duct work that ocurr during large throttle transients. I am not going to start pasting code snipets becuase i would be giving away proprietary information you will just have to take my word for it.

To answer you other question thee are 3 components in the VE table calculaiton.

Injector Size , MAF Airflow , Cylinder Size

Purrvert

Here is the end result of your tuning style, a little plagerism here, but I couldn't have said it better.

"I'll give you a basic problem I ussually see.

The car is dyno tuned with a given fuel rate by mass air calc. and injector flow rates. L-terms pretty much stay 0 on the dyno and the WOT A/F is set on the dyno with timing adjustments for the best power.

Now you start driving down the street with the air filter getting a different velocity of air and the computer starts to adjusting the L-terms to maintain 14.7-1 A/F. When the L-terms go + it also adds fuel to the WOT part of the tune. So,you left the dyno at 13-1 A/F,then the engine added +8 fuel at cruise which dumped onto the WOT table and the car has an LEARNED A/F of 11.5-1."

That is the simple way to explain it."

Gary Z

What is wrong with running MAFless (pseudo Speed Density) if the holy grail is to get WOT AFR to accurately track the PE table? This is quite easy if you tune MAFless and it is difficult otherwise.

muncie21

iTrader: (14)

So if we were discussing a theoretical PCM here...what would the code/formula look like?

There's been lots of discussion on what exactly the numbers in the VE table represent. One thing for sure, they don't represent volumetric efficiency solely.

slow2000z28

sorry its been so long since i looked in, (been putting a turbo on a friends h22 accord). im running w/o a maf b/c my maf is messed up. one sensor was hit when installing an intake and it has been off the charts since then. i bought the tunning software to tune the car w/o the maf anyways. that was what many of the people on here run, from the info i gathered when reasearching the software. why should i buy another maf when i can tune w/o it. some smoothe bellows and a tune and the car ran better than it ever did. i jsut reset my fuel trims then ran it and re tuned. car seems to be responding well. ive got a lm-1 wideband on the way so i can more effectively monitor things. thanks for all of the input u guys gave.