First VE tune, STFT and LTFT numbers

[puckyou]

Sorry, I don't have a scan but will get one tomorrow.

When I first hooked up the PT and scanned the car my STFT would bounce between +/- 5 and the LTFT would be around -12 at cruise and -22 or so at idle.

So after my first VE tune today I have the following numbers:

STFT +/-5 and LTFT now +/- 5 with the occassional blip to -6 or so.

Since I am new to this and learning as I go, does this sound like the normal thing that should happen?

Should I continue the VE tune another step? I guess I can always go back a step if I get less desirable numbers....

Thoughts?

[Sprucegagt]

You need to drive the car more before scanning. STFT values should be closer to +/- 3 or less. When STFT is constantly around 5 or higher then the car is still learning some. When that's happening you will be chasing the tune instead of completing it. When your done your LTFT values should be between 0 & -5. If you can get between 0 & -3, that's even better. But above all do not settle on + LTFT trims. If your adjustments make your LTFT's turn + then you need to backup and reduce the adjustment amount. Baby steps here will help.

[puckyou]

You need to drive the car more before scanning. STFT values should be closer to +/- 3 or less. When STFT is constantly around 5 or higher then the car is still learning some. When that's happening you will be chasing the tune instead of completing it. When your done your LTFT values should be between 0 & -5. If you can get between 0 & -3, that's even better. But above all do not settle on + LTFT trims. If your adjustments make your LTFT's turn + then you need to backup and reduce the adjustment amount. Baby steps here will help.

Cool, thanks. I will drive it more. So the initial VE tune should not push the LTFT's into the positive? If so, I should step back one?

I followed the directions in the table modifier exactly, baby steps? Since the table modifier is doing the work?

[puckyou]

In the table modifier I used the 100% as opposed to the 50% that the guide suggests. Maybe I will redo it using 50%.

[Sprucegagt]

Cool, thanks. I will drive it more. So the initial VE tune should not push the LTFT's into the positive? If so, I should step back one?

I followed the directions in the table modifier exactly, baby steps? Since the table modifier is doing the work?

Correct. The first adjustments you make should not make your LTFT's turn +. If they are then your using to much adjustment. The term "baby steps" is used to let you know to use small adjustments. That way you don't overshoot your objective. Remember, your just starting out with this, so you may find that a big first round of adjustments may not work the greatest for your car. Something smaller may be needed to get things working right.

In the table modifier I used the 100% as opposed to the 50% that the guide suggests. Maybe I will redo it using 50%.

I normally use 75% for the first adjustment if the LTFT values are way off. From then on I use 50% or less. I also like to have at least 15-20 counts for each cell before making the adjustment. That way I have a good average adjustment amount instead of relying on a few measurements. Don't worry about hitting all the cells during VE tuning, it won't happen. Instead just hit the cells you find during normal idle, cruise conditions up to 75+ mph.

[puckyou]

I'm going to start over then.....use 75% as suggested.

Thanks......

[geldartb]

my STFT and LTFT are the same as what he posted in the first post STFT +/-5 and LTFT now +/- 5 with the occassional blip to -6 or so.

but im runnin a diff setup and i dont have a supercharger.
05 3400 injectors at 55psi
05 3400 fuel and spark data along with maf stuff. runs pretty good so far.
i started out with that stuff cause when i would come to a stop it would want to stall sometimes. too much fuel. wasnt programmed for the new injectors.
i have yet to tune, gonna give it a try this weekend.

[puckyou]

Okay, started over, first with 75% and found that to be too high so I dropped to 60%. Now, with this general adjustment of 60% my LTFT's have dropped considerably to around -7 -8 for cruise with some -12 -14 in there for idle and -4 -3 for acceleration.

My question, am I looking for 0 to -3 for idle, accel, hard accel, and decel? If so, would it be more beneficial to tune each specific fuel cell or continue with the general tune?

[puckyou]

Just did some more research and found that I should not bother with decel as that will be addressed in MAF tuning later. I think though I am going to tune each fuel cell individually as suggested.....

VE tune - 2&4, then 3, then 1.

I cannot understand how global changes to all the fuel cells at once will get each one to -3 to 0 when they vary so much like mine:

1 idle: -14 to -12
2 cruise: -5 to -3
3 hard accel: -3 to -1
4 med accel: -4 to -2

How then do you tune idle, just log info while sitting idling, or use idle info from driving scan, (sitting at lights, etc).

I will conquor this tuning.....

[Sprucegagt]

Ignore decel (FTC 1) you do not need to worry about it. As for the other fuel trim cells (0,2,4), yes they should be between 0 & -5. Don't worry about FTC 3 right now. You need the others in line first. In fact if you are hitting FTC 3 then you need to take it a little easier on the throttle. Idle tuning is done just as you said, sitting in gear.

[puckyou]

Here is a small scan after a initial scan and changes of 60%......

LTFT in the idle are still very high, cell 2 is looking nice with -2 to -4 after one change.

I think I am going to get the idle's down in the -2 to -4 range before I do anymore general changes across the board.

thoughts?

[Sprucegagt]

Here is a small scan after a initial scan and changes of 60%......

LTFT in the idle are still very high, cell 2 is looking nice with -2 to -4 after one change.

I think I am going to get the idle's down in the -2 to -4 range before I do anymore general changes across the board.

thoughts?

Keep working on it. I take it you are selecting only FTC's 0,2&4 in the Table Modifier advanced options tab?

[puckyou]

Keep working on it. I take it you are selecting only FTC's 0,2&4 in the Table Modifier advanced options tab?

In the first VE tune I completed no, I changed all cells. This last change I just completed, only selected 0 cell or idle as I wanted to bring them down from -14
-12 to put them inline with everything else around -4 to -7.

Time will tell tomorrow when I drive back and forth to work.

This VE tuning is killin my tranny.......

[Sprucegagt]

Hold up Chief! Your doing this the long way. When you select the options in Table Modifier you can make the adjustments per FTC cells.

If it helps send me copy of your first VE scan when your tables were stock. I can make some adjustments and let you know what I did.

[puckyou]

Hold up Chief! Your doing this the long way. When you select the options in Table Modifier you can make the adjustments per FTC cells.

If it helps send me copy of your first VE scan when your tables were stock. I can make some adjustments and let you know what I did.

I though by only changing specific fuel cells each time would be the longer way as opposed to making changes to all cells to begin with. By what I read and thought I understood, you begin with changes to all cells, then pick specific fuel cells, to fine tune it, since changes to all fuel cells each time will only get you so close.

PM'ed you.

[geldartb]

ok im in the process of doing the same thing here and so i fully understand things here, anytime there is - numbers its taking fuel away and when its positive its adding fuel right.
just want to make sure im understanding what people are saying.

[puckyou]

ok im in the process of doing the same thing here and so i fully understand things here, anytime there is - numbers its taking fuel away and when its positive its adding fuel right.
just want to make sure im understanding what people are saying.

correct, negative number pcm is removing fuel, positive number, pcm is adding fuel.

One thing I DO understand is, we want numbers, at or around 0 to -3. sarcasm.

Getting there.......well thats another story.......but this learning process is interesting.

[puckyou]

Okay, let me try and explain where I am lost on this.

For example lets say you have the following:

Fuel Cell 0: Idle of -18 to -20
Fuel Cell 1: Decel so we don't use it
Fuel Cell 2: Crusie -10 to -12
Fuel Cell 3: Accel -6 to -8

So we take a scan and gain all this information, when we use the modifier and select to use hits of 3 and 50%.

Does the modifier realize the varying LTFT's between the different cells and correct accordingly?

What I am trying to say is if you are trying to reach 0 to -3 with general changes, how does tit happen????

[puckyou]

Okay, I looked at everything again.....and I think your right, I am attacking this the wrong way.

So, I used the scan that I emailed you and chose the following options:

# of hits 3.
Use LTFT and STFT box checked.
Chose FTC 0, 2, 4
If anything is between -2 and 0 don't change it

[Sprucegagt]

Sorry for the delay in getting back to you, but I do have an update.

Here is what I selected for the Table Modifier Export options:

1. Use LTFT and STFT box unchecked.
2. Hit counts set to 5. But redoing this with 15 from now on is recommended.
3. Percentage adjustment: 60.
4. Only use FTCs 0,2 and 4.
5. Fuel trim filter between 0 and -3.

With this it does give some large adjustments for your idle trims because they are so far off. You really do need to get your IATs down. They should only be just a couple degrees above ambient. If you have to move the sensor away from the exhaust crossover then do it. I had to do it for the same reason.

But the biggest problem I found was your driving during the scan. You can't just stab the throttle and let the car drift back down to 0 mph. Instead you need to be smooth and steady with the throttle. Slowly vary your speed and throttle adjustments from 0 to 4000 RPM. If your having trouble hitting some of the higher VE rpm cells then drive with the gear selector in 2 or 1. But whatever you do, do not go over 100 kPa.

[xonelith]

To support Spruce's comment about not punching the throttle, there's something called Acceleration Enrichment in our PCM's. Basically the computer will dump some additional fuel when the throttle surpasses a certain percentage (ie change in TPS or delta). This doesn't show up in your commanded afr as does PE.

In my stock tune, this percentage is 1.8%!!!!

I'm not 100% sure if i'm reading this parameter properly, but to be safe, you need to do gradual TPS changes or the AE will throw off all your hard work. As a side note, there is also DE (Deceleration Enleanment; sp?)

[puckyou]

Thanks, looks as though I will start over tonight......fresh.

Thanks for the recommendations, I try to drive at night so I can get the rpm's up without stopping for traffic, lights, old ladies in crosswalk, etc.

I will do slow, steady increase and then try to slowly decrease in cell 2 with my foot on the gas so I go down the rpm range the same way I go up the rpm range.

I am trying to understand the hit count......

Hopefully the tranny holds up, clunk, clunk, clunk.

My IAT sensor is located at the top of my SC, do I just remove it and plug the hole, I don't think I can move it back to the CAI piping.

[puckyou]

Spruce,

While looking at the table you attached and comparing it with my VE table, I don't have any 7.xxxx, 6.xxxx etc. All of mine at 0.86, 0.64, 0.50 etc.

[lastyear4gt]

If you are interested in moving the IAT, you're going to want to move it farther upstream from the blower to the intake manifold. Going before the S/C would screw up the readings.

[Sprucegagt]

Spruce,

While looking at the table you attached and comparing it with my VE table, I don't have any 7.xxxx, 6.xxxx etc. All of mine at 0.86, 0.64, 0.50 etc.

Sorry about that. I thought the VE table I used was not fubar'd. I'll get you another one this evening.

[puckyou]

Do you suggest that I start over fresh, or can I continue with what I have and work on better scans for the next round of tuning.

[Sprucegagt]

Start fresh. Your current scans will only make things harder to adjust.

[puckyou]

cool, will start relearning on the way home tonight....

[puckyou]

In order to make the scan more useful, is it wise to start the scan while going up the rpms easy then stopping the scan. Or should I continue to scan the whole time then tailor the scan in excel when I finish.

[Sprucegagt]

I would start the scan just after the car has warmed up. Then stop it just before shutting the car down. Also on second thought let me get a copy of your new scan when your done. I'll use it to redo your VE table.

[puckyou]

I would start the scan just after the car has warmed up. Then stop it just before shutting the car down. Also on second thought let me get a copy of your new scan when your done. I'll use it to redo your VE table.

Yeah, I had one tonight spent 45 minutes, up and down the parkway, kept the car in FTC2 from idle to 3800-4000 rpms, about 10 times in gear 3, then about 5 times in gear 2 and a couple in gear 1. Thinking okay, great scan, lots of info. Get home and only have a little due to the computer being in 25ms, as opposed to 50ms.......AGH!!!!!

I posted the little I retained, and let me know if I am on the right track.

[Sprucegagt]

Not bad. That's how you should be doing all of your scans.

[puckyou]

Okay, got another great scan today, touched on the following:

Kpa 20 2000 to 4000 rpms
Kpa 30 800 to 4000 rpms
Kpa 40 800 to 4000 rpms
Kpa 50 800 to 4000 rpms
Kpa 60 1200 to 4000 rpms
Kpa 70 2000 to 3600 rpms
Kpa 80 2000 to 2400 rpms

I would post it but the file is huge. Only issue I see it between Kpa 20 at the 3200, 3600, and 4000 rpm level I have positive trims, but I don't think that these matter.

[Sprucegagt]

I wouldn't worry about them. You only hit 20 kPa during decel.

[puckyou]

Okay, after the first scan and adjustments of:

Use only LTFT
5 hits
60%
0 and -3 no change
FTC 0, 2, 4

I ended up with the following changes. Per VE-SPLIT1 attached. Now according to that table and the adjustments made, I should not be in any positive numbers and overshooting the 0 LTFT. BUT, on my drive and scan tonight I was reading positive LTFT's between .78 and even 6.25 at or around 2900 rpms to 3500 rpms. How can this be????