Has anyone played with the volumetric efficiency table in LS1Edit? I've been following the discussions about wether its better to modify the MAF table or the fuel injector table to fix lean/rich conditions, but nobody has mentioned modifying the volumetric efficiency table. My car is running lean after having headers put on it and I'm guessing that an increase in volumetric efficiency is the reason. I plan to get LS1 Edit in the Spring and start playing with it but I'm curious why no one else has tried this yet?

- Mark

 

Correct me if I'm wrong, but isn't the VE table used only during open loop mode (mainly at cold start-up). On the early '90 to mid '90 cars, only a MAP sensor was used so in those cases, the PCM used the VE table all the time.

However, Our LS1 cars have a MAF sensor (as well as a MAP sensor) which is used all the time. I dont see why you would want to tune the VE table.

IMO, if you are tuning due to high LTFTs and the LTFTs are above 10%, tuning the MAF table is the most robust way to go. If the LTFTs are below 5%, then you could op to adjust the IFR table.

 

From what I've read it has been tried. The conclusion seems to be that there are more undiscovered tables waiting to be found. I Used the Inector Flow table to compensate for the Vararam. So far it's worked like a dream. Not only did this line up all my trims, but I was chasing spark knock and could not get rid of it no matter how rich or retarded I went. The knock is gone and the car is at 900v at cell 22. I had it as high as 950 with no results.

 

I agree the current VE tables available in LS1 Edit have no effect that I can tell at closed loop, only open loop. Currently I am tuning with both the MAF and Injector tables but I agree that we are overlooking something fundamental here and conclude there are more undiscovered tables that need to be done. We should be able to correctly calibrate a MAF and fuel injector to what it actually is, but alter another constant to bring the LTFT's back into alignment. I am dilgently looking for a solution to resolve this as I feel this is the key to tuning the cars correctly. Just my $0.02. :yesnod:

 

I would advocate the reverse. Make large changes to fueling and small changes to MAF, if necessary. The reasons have been posted in this section.

 

I agree too. You should NEVER change the MAF curve unless you change the MAF. Think about it. Would you change your O2's got get a closer LTRIM reading? YOu need to read the air correctly or it wil NEVER run right. You might get sorta close in a sense, but modifying the fuel tables is the correct way to tune for fuel. Don't try to fool the computer.

 

TooMany IDs:

Too Many Lies. NEVER complicate a computer problem by telling the PCM a bigger lie. Fix the problem by going to the root cause. If the MAF was modified, the root cause of high LTFTs is the MAF table, NOT the fuel injector table. IF the fuel injectors or fuel system has been changed, the root cause for high LTFTs is the injector flow table.

IF the MAF has been modified in any way, the MAF table does not match the flow characteristics of the modified MAF sensor any longer. This situation can be rectified by re-calibrating the MAF table. Having said that, it is very important that the method used to re-calibrate the MAF table must be technically correct. The process is not a simply multiplication thru the whole table.
:smash: :smash:

 

I felt that I could explain this a little better.

Lets think about all of the load states the engine can be in, really infinite, but lets accept many load states. The easiest load case to reproduce is the idle load case.

At idle, the engine will consume the same amount or air each second. It makes no difference to the physics of the engine which MAF sensor or type of MAF sensor is installed. Plain and simple!

Even though the same amount of air is going into the engine, each MAF sensor will respond with a different output frequency, no two types of MAF sensors are created alike. Recently, I idled my engine with two different MAF sensors, a GMAF and a modified ported factory MAF. The GMAF put out 2449Hz, while the ported MAF put out 2366Hz, for the exact same amount of air. The LTFTs were -0.8% (GMAF) and +13.3%(ported MAF). (I did allow the PCM to re-learn as I should have.)

The cause for the different LTFTs is that there is only one MAF table for the PCM to use to convert MAF frequency to MAF flow rate. My current MAF table has (estimating between cells) 6.00gms/sec at 2366Hz and 6.50gms/sec at 2449Hz. The flow rates are (6.50/6.00) 108.33% by relation.

The LTFTs add up to a difference of 14.1%, while the air flow values are 8.33% different. So some of you might see the non-linear relationship here between the LTFTs and the MAF flow rate. When I re-calibrate my MAF table for a different MAF sensor, I start out on the conservative side and alter the MAF table values by 1/2 of what I am trying to correct for in LTFTs. Example: If the LTFTs are 10% across the board, then I would make a 5% change across the board to the MAF table. BUT, the LTFTs are not all the same across all engine rpm states. Therefore, a complicated process must be used to properly re-calibrate the MAF table. Its not easy and therefore must people might decide to alter the IFR table (and this is OK for LTFTs below 5%) but then that may result in other complications because too many lies have been told to the PCM. If the LTFTs are about 20% and the IFR table is change 20% in an attempt to reduce the LTFTs down to 0%, this may spell doom to the engine at WOT.

 

Doc,
The first post didn't say anything about a modified MAF, did it?

I'm responding to the comment on positive LTFT's, which indicate a lean mixture. I would prefer to add the fuel to match.

Regardless of the algorithm you use to adjust the MAF, there are repercussions elsewhere (see other posts for detail). Adjusting fuel flow is more direct and the impact is limited to what we want to change, it's the easier path.

As for truth/lie, etc... call it what you will, makes no difference to me. I have SVO 30# injectors in the car, using the stock injector flow table. I guess that's a lie if you want to call it one, but the entire reason for the new injectors was to get the extra fuel. Scaling the injector flow table based on their size, would have put me back to where I started.


[Modified by TooManyIDs, 12:48 PM 1/12/2003]

 

Was the GMAF neutral or calibrated to alter the mixture?

Doc,
I just don't agree. Changing the injector flow table by large amounts (I've done up to 16%), doesn't spell doom for anything. It alters injector duty cycle and if that gets too high, larger injectors are called for.

Maybe we should collectively build a list of the negative impact of MAF table alterations. I've seen a few varieties go by and didn't note them all, so don't take the following as exact, I welcome clarification.

1. Grams/Second is used in the Grams/Cylinder calculation. Alter the first and you change the second. Now, use LS1Edit to see what tables would be impacted by that change. Start with the high/low timing tables.

2. I believe I've seen someone say the PCM doesn't recognize a Grams/Second value above a certain ceiling. I don't recall what the exact number was.

3. Don't we have some kind of secondary checking between MAF table values and the volumetric efficiency tables? Others have thrown codes, when the two have gotten too far out of sync.

That's all I can recall for now.

 

All lies are not the same. ;) Some are smaller, some are bigger, some have greater consequences than others.

My own position is the same as Godspeed's, namely that there's one or more VE tables and/or fueling equations that we don't have access too. Assuming that's correct, neither the MAF nor IFR tables are really the Right Place to make adjustments.

Since we don't have access to the Right Place, a Next Best Place (or Places) is needed. Since adjusting the IFR has such limited consequence (add or subtract fuel only) I tend to prefer it to altering the MAF table. Anything that's a function of load or torque (and that's not a short list, I would also bet not completely known) is likely to be impacted by MAF table adjustments.

Al, your third item is related to the P1514 DTC.

I like that people are challenging tribal knowledge. :cheers:

 

ToplessTexan:

I'm ready for that beer, how about you???

We do not have access to the fueling equation, the equation that determines the injector PW. However, as you know, we have access to many tables and several of these play a big part in the fueling PW equation. At part throotle, we have the injector flow rate table and the MAF freq/flow table. For WOT, we have these same tables, but also at least two PE tables, one vs RPM and another vs temperature. With these tables and the timing table, we can do alot of tuning on any LS1/LS6 car. We do not need access to the actual PW equation.

TooManyIDs:

About the GMAF, I bought it new and it is advertised to be "calibrated". The GMAF appears to be closer to the stock MAF for frequency response than my ported MAF. The MAF table that yield my posted LTFTs is a modified MAF table to closer match the GMAF.

Your pt 1) If re-calibrated correctly, the re-calibrated MAF table will bring you back to the same cell in the GM timing table. Now it is possible to loose some timing, but that is only due to the fact that the GM timing table is on the conservative side, it has to be on the safe side to stay away from KR. If there is a little timing left, the timing table can be adjusted on an engine to engine basis. The stock table represents the 99 percentile factory stock car. This table is not designed to get the most out of a modified engine, not even the stock engine for that matter.

In my MAF test posted above, my point was that each MAF will respond with different frequency output even though they are both flowing the exact same amount of air. Given that, each MAF requires its own unique MAF table.

Your pt 2) Yes there is a ceiling, it is 511 gms/sec. If you try to put in 512 or a higher value, LS1Edit will respond with an error. My highly modified LS1 car will see at full throotle WOT at 6,000rpm about 10125Hz max which is 315.91gms/sec in the MAF table. I have an LS6 intake, MMS stage 2 heads, 218 cam, and FLP headers, etc. BTW: The MAF table goes up to 12000Hz.

Your pt 3) I dont know of any connection between the VE table and the MAF table. Besides, if the MAF table has some problem, it is due to the fact that it was not re-calibrated correctly. I have heard of someone having LTFTs around 15 to 20% and go into the MAF table and multiply thru by 125.0%!!!!!
No, No, No this is not the way to do it.

About my GMAF MAF table, the value in the 10125Hz cell is 315.91 gms/sec while the stock MAF table has 302.31 gms/sec, a difference of 104.3%... In the 2500Hz cell, the GMAF table has 7.48 gms/sec, while the stock MAF table has 6.80 gms/sec, a difference of 110.0%. So what I have been trying to say is that re-calibrating the MAF table properly is a non-linear process. In my specific case for the GMAF (even though it is "calibrated"), at the top end I changed the value by 104.3%, while at idle I needed to change the flow value by 110.0%. At WOT, I have gotten 28* timing with the stock MAF, ported MAF, and the GMAF. The reason for this, I have a re-calibrated MAF table for each MAF. So I have not lost any timing, in fact, I am still running the stock timing table. This table is my next target in search of my top end HP.

Do you think that I could/should be able to pull more than 28* timing at WOT with an LS1 engine??? What is your experience here?? I could use some advise. TIA.

:steering:

 

i didnt read every bit of this entire thread but it seems the original question may not have been answered completely. The VE tables will only come into play mainly during Speed Density operation. Our cars use a MAF as its core reference instead of the MAP, so, adjusting these tables will not yield any improvement in LTFT's or otherwise. If the MAF were to fail, theoretically the computer goes to SD mode, then the VE tables come into play. However, in my experience, any time there is a MAF failure (calculation, hardware, etc), the PCM goes to Reduced Power, or limp mode.

I would like to interject on the MAF table discussion that has promulgated here: I would not use the MAF table to tune with. I have been very successful using only the Injector Flow Rate table to tune my ltrims. I have found that it is very easy to screw up the MAF table to the point where you get lost, especially when changing segments of the table vs scaling. the end result usually ends up being a car going into Limp Mode due to a MAF Calc out of range error. Leave the MAF table at default.


[Modified by rwj383, 1:47 AM 1/13/2003]