Fast Toys Performance Parts

iTrader: (3)

I have a stock internal 2001 Corvette that has a different intake, ported TB and exhaust. Like many corvettes with intake mods, LTFT's are 20-25 % which triggers the SES light with the lean code.

I searched through MANY MANY posts on what the best method is correct for the LTFT's.

The 3 methods seem to be:

1. Recalibrate MAF table
2. Recalibrate VE table
3. Recalibrate IFR table.

There are many arguements for an against each. The injectors and MAF are both stock.

What method are people using that produce the best results? Please post your pros and cons.

Thanks!

Cheatin' Chad

iTrader: (3)

I have done all of the above and what I settled on finally was working the MAF tables.

When I got the +25 I first just added 25%more fuel via IFR. I did this to check to see if I was seeing mechanical problems or if this was something that needed to be corrected with tuning. I was unaware at that time that this was a common problem.
Adding the extra fuel immediately corrected my trims. So I returned the IFR to the correct setting and started working the MAF tables until I got my trims were I wanted them.

As I see it the engine is seeing more air therefore the MAF tables should be adjusted to allow the PCM to work properly. When you change the IFR to get more fuel you are "tricking" the PCM into doing what you want.

I figure "garbage in garbage out" Keep things correct so the mathematical equations the PCM is busting out to keep the car running are correct.

Although there are alot of extremely knowledgable people here It seems that no one here can really say exactly how many things are affected by the many different tables we can modify. If we screw with one thing it may affect many other things.Yes, over the years guy here have figured out ALOT!(way different than when I started with this just a couple of years ago) but I still think there is more to find out concerning this. I assume by "tricking" the PCM you can create alot of little headaches for yourself.

Frost

iTrader: (45)

+1 for working the MAF table.

Doc99SS

iTrader: (2)

Lets think about this,, what has been changed from stock? Not the MAF, so the MAF is completely stock, no specials ends and still has screens (if screens are stock). Right. Therefore, changing the MAF table is not the way to go!!!

The injectors are the same as factory, therefore, do not touch the flow tables.

This only leaves the VE tables.

I think that what you want to do is to scale the VE tables up in the fuel trim cells that have high (+20%) LTFTs. Scale up 10% to start and data log the result. Scale up again if necessary, and re-data log. You will want to tune the VE tables until the LTFTs are between 0% and -5% while driving around (I call this cruise mode)... With this, the LTFTs will not add any extry fuel while in PE mode (WOT). If you need more fuel at WOT, use the PE fuel tables to get the needed fuel. Do not run lean!

Doc99SS

iTrader: (2)

I wanted to add a little to my post. --- The LTFTs are positive, therefore the computer is adding fuel while you are driving around, and you are pegging the amount of correction the computer allows resulting in a SES light. There are 16 drive around fuel trim cells (0 thru 15) and several other fuel trim cells for idle and WOT operation. The 16 drive cycle fuel cells are arranged in a 4 x 4 pattern which overlays on the VE table. If you change one cell or a few cells in the VE table, and then go out and test drive, you will see how the fuel trim cells and the VE table are related. You could change only one fuel trim cells (say #10) from +25% LTFT to +5%... But you want to change several at the same time.

Since the LTFTs are positive, you want to get the computer to add fuel via the normal fuel calculation. You achive this by increasing the values in the VE table. I am not an expert at the VE tables, but I believe that this is the best solution to your new intake and TB situation.

Redline-Motorsports

iTrader: (3)

I agree. The IFR table should not be adjusted as its a constant based upon static flow rate. It was a quick test in Cheatin's situation..........good call.

The MAF is one way to correct the airflow modeling of the engine but the proper way is to get the VE table in line first. As usual there is more then one way to skin the cat!

Doc

iTrader: (9)

So what are the particulars of the intake and exhaust? FAST, LS6, Sheet metal? What Torque specs did you use?

Exhaust, LT's, clamps, flanges, welded?

25% both banks?

Stock injectors, internals, with all of indications you have provided point towards a massive amount of uncommanded air; intake/exhaust leak(s). These pcms can compensate for alot of error, best bet is to fix the problem.

DrkPhx

iTrader: (15)

Exactly right. If the LTFT's on both banks are that lean setting codes, there is a problem. Is the MAF stock?

edcmat-l1

iTrader: (10)

First off, it sounds like something else is wrong with the car. LTFTs usually arent off that bad from just an intake and t-body. Sounds like a contaminated MAF.
As for tuning it, if nothing is wrong, VE is the way to go.
Maf is stock, leave the table alone. Injectors are stock, leave that table alone.
Run it in SD, and if the fuel trims end up closer, the MAF is contaminated. If they are still off, dial in the VE table while you have it in SD, then turn the MAF back on, and everything should be fine.
Tweaking the MAF table will work, its the quick and dirty way of getting the fueling in line, but my exp is it causes some driveability issues (scaled MAF+stock VE). Some that people have and dont even realize it. Like "soft" bottom end, poor throttle response, etc.

Full-Force

iTrader: (11)

Positive fuel trims that high sound like a fuel delivery problem.

Frost

iTrader: (45)

The problem with leaving the MAF stock is that NO ONE leaves their intake tract stock.

A friend of mine is parting out his car and I have been woring his tune as he pulls each mod to look at results. One of the LARGEST changes came from just a lid... something that nearly every car has. This change alone alters how the MAF perceives the world from what was intended and corrupts the factory's table.

His car went from TIGHT trims that were 2-3% negative all around to +8 to +11 LT once learned out. All he did was remove the MTI clear lid and return to the stock airbox for his Z28. Am I to believe that REMOVING the performance lid and replacing it with a restrictive one that makes lower proven dyno numbers that it should need 10% MORE fuel in cruise and light to moderate load areas? Hell no. But what HAS changed is the way the air moves through the MAF. That is why you can't just leave it stock. Most of the fueling the car will see comes from this table, not the VE. Make a perfect VE and re-enable the MAF and see what happens; your fuel trims are off. If your VE was close and the stock MAF table was good, why would you wager this would happen?

Fast Toys Performance Parts

iTrader: (3)

The MAF is stock with screen attached. There are no leaks. The Corvette just has an aftermarket air intake system and ported TB. It is very common on Corvettes to throw an LEAN SES code after an intake install.

It still sounds like lots of debate on the topic! I just want to do this once LOL.

2002_Z28_Six_Speed

iTrader: (19)

Personally, I have always thought that it is where the air is flowing in the intake tract. Maybe when you change the intake it doesn't hit in the same area of the resistors as much. It might flow off to one side more or the other.


--------------------------


Of course if you only tune half the car (VE or MAF) you will always be missing part of the picture. Sure .2 seconds of 18:1 might not hurt something but transistions derived from the VE have to be nailed down as well steady-state from the MAF.


That is just my 2 cents. Correct if wrong.

The Dragon

iTrader: (6)

I think the main problem causing this debate is that so many people on this site do not remember a stock question with such minor/few modifications

If there are no intake/exhaust leaks, I am positive that your "lean condition" is stemming from your ported throttle body It happened to me waaaaaaaaay back when

The best way to tune would be MAF/VE . . . if you have a LOT of time to log-tune-relog-retune, etc., etc.

The fastest way, while still getting the job done, is IFR/VE. A LOT less logging and re-tuning I've done ALL of the tuning options available and for someone who doesn't have hours upon hours of time to devote to your "basically-stock" car (being a business owner I'd imagine you'd fall into this category ) . . . make a general adjustment in your IFR table and then tweak the VE where necessary.

If you plan to modify your car further in the future, which is most often the case, then you will need to upgrade the factory fuel injectors to larger squirters . . . which will require a modification to the IFR table anyway.

As mentioned earlier in the thread, there is more than one way to skin a cat . . . a longer, medium, and short way

jimmyblue

iTrader: (11)

Before you get all excited about changing air / fuel
delivery models, take a step back and make sure the
trimming "impulse" is real and not a sensor artifact
(bad / cold O2 sensors especially).

Putting the car open-loop hot, and looking at the
delivered AFR in cells where you've seen high trims,
is a good way to start. If it runs better open loop
than closed (i.e. closer to commanded AFR comes
out the pipe) then look to the sensors, exhaust
config / leaks, etc.

Rhedalert

iTrader: (21)

I too have very minor mods, and with everything hooked up, my LTFT's were way high, between +7 and +25 (maxed). These numbers were high even without the ported TB or induction. I thought maybe bad O2's, failing fuel pump, etc given my mileage. I disabled the MAF with my tuner and the numbers went down to +-4. Tuned the VE table for minor adjustments and it's good. So in my case, correcting the VE is not going to correct my trims with the MAF enabled. MAF has been cleaned since the day I got the car, but I still think there will be an issue.

Doc99SS

iTrader: (2)

Fast Toys: you said that the MAF is stock and even still has the screens,,, therefore, you can do whatever you want upstream from the MAF and it will not effect the MAF flow characteristics,, because the screens regulate any incoming flow to turbulent flow.
(Now lets dont have a discussion on turbulent flow or not, it does not belong in his post)
Like I said above, I am a MAF tuner guy, but in your case, tuning the VE table is technically the correct way to go.

By contrast, if you had acceptable LTFTs with your setup, then you altered the MAF (like removing the screens or install a GMAF), and the LTFTs changed, then the correct solution in bringing the LTFTs back "home" would be to modify the MAF table.

Fast Toys Performance Parts

iTrader: (3)

I agree. The MAF hasn't been modified but it is common for cold air intakes to through LTFT's out of line. The VE table is probably the correct way but with LS1EDIT and no histograms, it would be much more completed. The MAF table tuning wouldn't be too bad but then it screws up the timing table as well. I think I will try the IFR table.

BTW: The car was pegging the LTFT's even before the ported TB with just a Donaldson Blackwing.

jimmyblue

iTrader: (11)

What I see here is, you don't know which element is the
cause of fueling error. So you can't pick which **** to
twist with any sense.

You can do a not-bad job of VE tuning with the narrowbands
provided they are lit and you maximize the time spent at
1.000 commanded EQ (hold off PE, lower timing if need be).
It takes more time but you just keep raking through the
table adding where O2s show low and subtracting where
they show high, and leaving the middle alone. It might
take you 4 or 5 passes like that to get pretty tight.

But you really want some idea of what's at play.

If your 5000RPM Dynamic Cylinder Air is less than 0.75 g/cyl
I'd suspect the MAF. If it's 0.8ish that's sensible for low mods.
If your dynamic airflow and MAF airflow disagree strongly down
low this probably implicates VE fidelity if >4000RPM g/cyl is OK.

It's a pretty good bet that the injectors have nothing to do
with it, but you might check fuel pressure vs 58PSI nominal.

Slowhawk

iTrader: (12)

Start simple.Make sure the MAF wires are really clean. Then make 100% sure there are no vacuum leaks,expecially in the PCV system.