GuitsBoy

iTrader: (4)

Hi all -

Ive been trying to figure out what everyone is doing with VE tables. I dont understand anything about it no matter how much I read up. Im sorry if my questions seem very elementary.

Does the Main VE table affect normal closed loop driving? Or does it only affect startup and throttle transients? Ive done most of my fuel trim tuning via IFR and the MAF tables. I have however scaled down the first three columns in main VE by .85 .92 .97 to try and eliminate some surging i have had with the stock cam ever since the car was new. I have not disconnected my MAF yet. Do I need to disconnect the MAF in order to tune VE by the LTFTs? Will those change not matter once the MAF is plugged back in? My head hurts.

Thanks,
-T

EDIT: Oh, I forgot to say, I have both a stock and ported MAF. I did my initial tune with the stocker and then only changes the MAF tables. Neither tune is terribly pretty though.

jimmyblue

iTrader: (11)

There were some long-winded threads (check the stickies
if you have a lot of spare time) about it. The upshot as I
see it is -

Unsteady MAP = SD only; throttle transients / tip-in.

>4000RPM, steady MAP = MAF only; WOT

<4000RPM, steady MAP = "blended" MAF/SD; favoring
SD more as you decrease in airflow/RPM. Idle in my
experience is nearly all SD.

How your FTC boundaries are set up, has a lot to do
with how consistent the "partitioning" is within each
cell. Stock late F-body has one cell for 2500-6500 RPM
in each of the MAP steps. This straddles a lot of
changing-basis territory and leads to LTFTs that drift
continuously based on short-term driving pattern (did
you spend more time below 4000RPM, getting pushed
by SD, or above 4000RPM, getting pushed by MAF?).
The idle-2500RPM "bin", similar deal - a highly varying
VE map down there and a varying degree of MAF
"contribution" too. Slice it finer and get more intra-
cell consistency, less chasing the weasel around the
mulberry bush.

jimmyblue

iTrader: (11)

Let us know how EFI 102 goes for you.

HumpinSS

iTrader: (1)

What about MAF sensors that are affected by reversion and changes in the intake tract. Can you still rely on them to e reliable in their reportings?

Bryan Wilkinson

iTrader: (1)

I had already taken the class last weekend in GA. Anyone that has any interest in doing even the slightest modification to their car, should take this class. I found that it cleared up a lot of myths running around on the forum.

The best one was how a/f has nothing to do with power.

I highly recommend the class.

Bryan

Plan B

I once met a guy who bought a house from a builder. This house had all the good things inside and out however, there was a slight problem with the way it worked for its new owner. It was nice to look at from the front and it certainly had all the best gear inside, but the owner wasn’t really that happy with the total package. So, he started to ask other builders and architects to help him with the problem. He looked around and found an experienced person who was willing to guide him through his purchased architecture and help with the build rectification.

This new person helped rebuild the steps at the front for easy access and then demonstrated how to open and shut the lounge room curtains, so the new owner could see the light and the shadows cast upon certain objects within the house. The owner was extremely happy and started to tell the world about “curtains and steps” with very little understanding towards the rest of the house.

HumpinSS

iTrader: (1)

Understanding what you wrote i have a few more questions. If the lid changes how the air flows across the resistors in the MAF wouldnt this now e a source of inaccuracy. Also the MAF doesnt know which way air is traveling. If you ahve a decent cam with some healthy overlap I would think this would affect teh maf due to reversion and the air/sound pulses coming back out of the intake. Since the Maf uses bth temp and frequency to measure the movement of air (not the density or weight that implies pressure and that is the MAP sensors job) it would seem to me reversion would cause the MAF to theorectically measure teh air twice thus confusing the PCM into thinking it is very lean and pushing the trims ways positive.


If this isnt the case can you explain to me why when my maf is plugged up (stock unmolested MAF) with my 230/232 cam with 68* overlap or 11* @.050 my trims all spike at +10 or more. This seems strange to me because this was seen with the stock tune. Now we all know when a cam is added to an EFI car because of the lack of vacuum at idle the computer thinks the car is under load and tries to compensate by adding fuel. Sicne the o2 sensors close the loop and realize the car is running real rich it starts subtracting fuel via the trims. While my maf sensor was plugged up I seen none of this happening. All i seen was + trims that wouldnt move no matter how i moved things around. AS soon as I unplugged the maf and removed it from the loop EVERYTHING fell into line. All my trims went - like they shouldve so I decided not to deal with the headache and eliminate it all together.


For someone that is seeing this (not only me but a few other members) how would you tune the car in order to maintain the use of the MAF or are you gonna be tight lipped

J-Rod

Here is what Chris at HP tuners said in a thread about the way he tunes SD. But I think there are tips in here you can use for MAF tuning also.

Chris@HPTuners
HP Tuners Owner

Email | Instant Message

Posts: 1143
Re: MAFless (what to do?)
« Reply #10 on: Sep 26th, 2004, 7:57am » Quote | Modify

--------------------------------------------------------------------------------
yeah, just disable the SES. A GTS will still show P0102 from the factory.

Here's how i do it:

1. connect WBO2
2. disable closed loop, lean cruise, COT, etc..
3. set open loop f/a to 13.0 (or whatever)
4. set PE to 1.0
5. hold various points in the VE table on the dyno and note the AFR difference from 13.0
6. increase or decrease VE table depending on the AFR (if the AFR is higher than 13.0, increase VE)
7. once i get close to 13.0 across the VE table the set your PE table to 1.14 (12.8 AFR) should see 12.8 on the WBO2. If you are aiming for a flot 12.8 acorss the WOT fuel curve then your PE table should be 1.14-1.15 across the board. Yo can usually run a bit leaner in the lower RPM range say < 3000 rpm. A stocky will be commanding 13.5 AFR for example at lower RPM.

The goal here is to get the commanded AFR to match the actual AFR you are seeing on the WBO2 my changing the VE table, and without external influences such as fuel trims.

If you don't have a WBO2 then you can achieve similar results just using your LTFT's in closed loop (use the histogram and aim for 0 or slightly negative trims). Make sure you log commanded AFR and that it reads 14.7. Although you'll also, probably have to wing it a bit in the upper RPM and MAP ranges as i don't recommend trying to maintain 14.7:1 at high load/rpm.

I think LTFT disbale is in v1.5 so you should be able to disable LTFT's altogether and tune using STFT's as well, which move faster.

Hope that helps.

HumpinSS

iTrader: (1)

Good infor J-Rod. My SD tune was based on the LTRIM learning. I did try the open loop WB tuning but realized it wouldve taken longer than i was willing to fight with the car so I used the stock o2's which cant be beat for 14.7 to tune the ve table. when the WB integration cable comes out it will make this a lot easier since I wouldnt have to sit down tablulate and average data. It will all be accesible to us in the scanner/histogram table. Until then I only use the WB for track passes and when in the pits I go back and manipulate 12 seconds of data

Bryan Wilkinson

iTrader: (1)

As I feel that I am already over my head. I will try to give an answer without making my situation worse. I agree with everything you have said, almost. I don't believe I was trying to explain how to tune a car, as I am not 100% sure how to and if I did, I wouldn't do it, not because I don't want to share information, but I do not want to be responsible for sharing the wrong or misleading information.

From the class I took I obseverd the following, If I have misunderstood what I was being told, I apologize. I do believe that the MAF sensor does indeed measure the weight of the air or Mass of the air that is flowing through the sensor, based on Freq and temp of air and it is measures in grams per second. The MAP sensor measure the pressure of the air in kilopascals and it measures the air in atmospheres. Both individually are used differently to get to the same end point. But the MAP sensor does not assist the MAF sensor to calculate the mass of the air. In the new systems GM/ECM the MAP is a backup sensor used as a check against what the MAF has to say. It is my opinion that the MAF is not as acurate as the MAP.

My information was obtained from "How to understand, service, and modify Corvette Fuel Injection & electronic Engine Management 1982 - 2001. by Charles D Probst.

And from EFI University class entitled EFI 101.

Again this information is subject to interpretaion. I may not have fully understood what I learnd in class.

I currently have a stock MAF on my car, but I am working with some very kind people to remove the MAF from the car and work on the MAP alone in a speed density tune.

I think it is best that I hold in reserve any further comments as I am not an expert by any means. The PCM holds entirely too many tables and events for me to be making suggestions. In my limited experience I do understand the MAF and MAP and how they work, but that is a very small percentage of the equation compared to everything else in the engine and PCM.

I apologize
Bryan

Bink

I don't know how to get by the O2 sensors - closed loop re: Emissions. Open Loop and scaling the MAF at idle seems to work with my car. I have 33* overlap at .050". FWIW.

joel

jimmyblue

iTrader: (11)

I have seen some pretty reasonable looking explanations
of how the LS1 PCM uses both MAF and SD, from people
who waded through the code. It appears peculiar but
sensible in light of the MAF's strengths and limitations,
and matches my observations from tune fiddling.

The MAF is an instrument which can easily be corrupted
(by airflow bias, physical modification, contamination)
and in the case that physical errors can't be removed,
the cal is the next best thing to change. Realism in all
things makes tuning straightest.

I would expect the class did not go deep into any single
engine's detailed fuel management algorithms, in the
interest of a more generally useful coverage. But the
details of how and where the MAF, SD or combined
airflow calculation are used matter a lot if you are
trying to tune specific operating regions on these cars.

The first code-interpretation-based descriptions I've
seen well post-date the Probst book. People are still
figuring out all the internal goings-on of the LSx PCM,
5+ years after introduction.

Bink

Here's a link to gameover's Airmass Calc., SD and MAF Thread.....it's the most authoritative in regards to the Airmass Calculations (MAF and SD).

http://www.hptuners.com/forum/YaBB.p...num=1078851555