kindaslo

Working on a 97 vette 408 stroker ported heads big cam blah blah.

Car idles, and drives decent, but when I go to adjust the primary VE Table beyond a point the car goes into reduced engine power mode. I've backed fuel out of the ve table and the car is good again, but really should have more fuel to get the ltft's to the desired location.

What I do know, I've rescaled the calc airflow p1514 table by 120% and it fixed the problem, until i started adding mroe fuel. I'm hesitant to rescale this table further. Are there any ill effects from this, I understand it is a matter of the VCM seeing one value and expecting another. Is there a way to tell the VMC hey this motor moves more air than you are used to understand it?

Help is appreciated in advance.

HumpinSS

iTrader: (1)

The tables is just a test table you can rescale it again and rebuild it when you are done using a histogram providing you have EFILive or HPT

soundengineer

iTrader: (16)

yeah...just keep upping it till problem goes away...its just there to tell the PCM if there is a problem and to set an error code....doesnt really do anything else

kindaslo

Thanks for the input guys.

Steel Chicken

iTrader: (3)

MAFless?

kindaslo

YES I hav the maf frequency fail set to 0.

Steel Chicken

iTrader: (3)

OK, because when the MAF calibration is off it can interfere with accurate SD tuning, ive experienced that personally, very frustrating till i figured it out.

not to be insulting, but I assume you modified the engine displacement table (cylinder displacement) table as well?

soundengineer

iTrader: (16)

ok..it doesnt work that way....teh MAF calibration can NEVER interfere with SD....
The MAF can be effected by a bad VE table...as the car uses the VE at basically any throttle change greater the 1% and before 4000 rpm.....
but an SD tune cannot be effected by MAF in any way shape or form...

I can skew my MAF table so bad that it wouldnt run no matter what I did with the MAF on....turn it off by setting the fail to 0 or by disconnecting and my car will run perfect

the thing that a badly calibrated MAF will screw with is transmission Shift tuning as it is used on some cars to determine engine load

Steel Chicken

iTrader: (3)

I respectfully disagree. I installed Long Tubes, and tried to get my Long Term trims down. They kept reading lean, lean lean.
Id add fuel to the VE, flash, do it again. after 3 times doing this the car ran like doo-dee. I went back to a pre header install bin, recalibrated my MAF, and then I was able
to tune the car (ve tables) one time. Somehow, someway, the MAF was screwing with my LTrims keeping me from getting a good SD tune. This was with power enrichment disabled.

I had a thread here somewhere going in detail.

soundengineer

iTrader: (16)

IF you had teh MAF enabled then its not an SD tune.
you should always Tune VE first with MAF Disconnected or fail set to 0
the VE is responsible for all non steady state conditions(steady state is defined by tables in your PCM which we can edit if we so desire)
your MAF is only used in steady stae conditions.
IF you try to tune the VE table with teh MAF connected and turned on to normal use...then you are not tuning the VE..you are running off of teh MAF and VE combo...and you will get horrible results.
again...you cannot properly tune the VE tables with the MAF attatched and in use normally. you must either set MAF fail to "0" or disconnect the MAF all together. Then and only then are you in "Speed Density" mode and you can properly tune the VE

and coversly..tuning the MAF before you tune VE is also incorrect....(unless you are a v6 in whcih case it doesent even use the VE unless your maf goes bad or is disconnected)
teh MAF is only used in steady state and unless you can filter out ALL non steady state activity..then the calibration will be wrong..unless you calibrate the VE properly in SD mode...in which case teh MAF and the VE will match so it is a way to control bad data from entering the equation... IF VE is dead on 14.7..and you tune a MAF to 14.7 teh average is still 14.7
if your ve is off..and for easy #'s we'll say its commanding fuel equal to 15.0
and we again shoot for MAF of 14.7 but its commanding 14.0...well steady state its going to run 14.0, and part throttle under 4k its going to run 15.0...
skewing trims....and amking it impossible to tune because they will always be screwed up from one another.

ad heres a good article MAF vs Speed Density
http://www.carcraft.com/techarticles/24549/

Steel Chicken

iTrader: (3)

I see what your saying, but I had MAF fail freq turned to zero. Maybe I should have just unplugged it.

Red12secZ28

iTrader: (2)

I had the same problem. Have you adjusted the etc predicted airflow table. When I went speed density I would get reduced engine power codes Po1514.
I put a cam in and instantly would go to reduced power. When I was in normal closed loop It would close the throttle blade at wot. It was almost like the rev limiter.

joecar

When MAF is disabled by setting fail freq to 0,
the PCM must throw a DTC (top of my head: P0103),
otherwise you're not in SD mode.

Unplugging MAF will get you SD mode.

kindaslo

I have made the cylinder volume change.

ETC predicted airflow? Have not worked on that one. Can you give me more detail as to what changes I should be looking to make and why? I ask why now because I have gotten a lot of bad tuning advice from people that say "it's just how it works" lol.

joecar

When increasing the values in VE table, you must also increase the values in the predicted airflow table(s);

PCM compares airflow (computed using VE table) with predicted airflow, and if computed airflow is greater, PCM thinks there is a problem, throws a DTC and enters reduced power mode;

while SD tuning, just increase predicted airflow by some large amount;
when finished SD tuning, log airflow into a histogram/map, increase by 20% and paste into predicted airflow table(s);

there are various threads on this and other forums regarding this topic.

Red12secZ28

iTrader: (2)

The table your looking for is in engine diagnostics, then under etc,finally etc predicted airflow in Efilive. I don't know where it is under hptuners or edit. Cleared my problem up.

Pavetim

iTrader: (15)

Hate to hijack this but seems like you guys know your ****. I think i'm getting the nitty gritty here but i'm confused on the generals. So first i'd unplug the MAF and tune that way right, which gets the car in tune, then you plug it back in and tune. But the thing i'm missing is if the car always tries to keep it at 14.7 AFR what is the purpose of tuning in MAF mode?