Tuning VE with LTFTs

[PerformanceTurbo]

I've been trying to tune the VE on this H/C 00 TA forever it seems. I have logged probably 50 miles worth of LTFTs and modifying my VE table each time. The problems I am having is Every time I change it, and go to re-log, the LTFT cells from 0.8 to 3.2 RPM and 20 to 60 kpa are always showing over -10. All the other cells however have seemed to learn themselves well, only hitting about -5 at the most.
The only thing I can think of is when I go to smooth the VE table, i am using HPT's smoothing and not hand smoothing it. Is it imperative that you hand smooth the sections that are high/low?

[12secSS]

I never use the HPTuner smoothing feature, I always hand smooth everything. After a while, you will begin to see how the VE table trends happen. Are you resetting the fuel trims after every flash?

[ChrisV 02 - Z28]

Are you in speed density mode with the MAF dissable/unplugged, maybe you are getting signals from maf and maybe thats why you trims are remaining the same???

[muayyadf1]

I was getting this problem. It was my wrong procedure. Every time I modify the tables I don't reset the trims. Now I reset after every major change and now things gone better. Tune with SD first. Modify your VE table, reset and scan again for +1 to -4 or around it. Then re enable MAF, reset trims and scan LTFT's against MAF frequency in Hz's. Copy LIFT's you get and paste special them by Multiplying % them into MAF table. Reser trims scan again. Now tune the VE table by LTFT's.


that is what I learned form my experience. May be I'm wrong but it works for me until now.


but when my engine heat soaks after a shut down things go a bit crazy. So I complete things in the next day when the engine is not heat soaked.



Just my 0.02 cents

[PerformanceTurbo]

I guess didnt reset the fuel trims.. I thought they were reset anyways after every flash?

[robison_02SS]

I am still learning but I am trying to understand the fuel trims.How do you reset them?is it just changing them or is it rewriting the calibration?

[gold98Z28]

I am still learning but I am trying to understand the fuel trims.How do you reset them?is it just changing them or is it rewriting the calibration?

thru the scanner vcm controls, under fuel tab.

[rushhour]

Boy is this a timely thread for me.

I started the process yesterday to get the LTFT's in line - they were running +12 to +14. Disconnected the MAF, reset the trims, ran it for an hour under various rpms. Logged the LTFT's after an hour.

As a side note - the scan (attached showed my LTFT's after learn as all negatives, I thought this was counter intuitve - since the LTFT's with the MAF hooked up are all positvie) I was trying to add fuel based on the "normal" LTFT's so I changed them into a a positive. Probably a mistake on my art - this is a first tiem for me.


I changed the VE by pasting - special - add, the LTFT's into the VE as postives. Seemed to be good - idle was .07 and other areas about -5.4 once MAF was rehooked up and drove it for about 20 minutes.

Took it out for a 2nd drive with the VE changed and then all of a sudden the Idle at a light started to go nuts, dropped down to -18 and the car started to die.

I was debating if the MAF had something to do with it. the car was tuned by another person for WOT on a dyno after heads/cam was put in and the MAF Airflow vs Output Frequency table was changed from stock (ie reduced).

I was wondering - should I paste the stock 04 GTO A4 MAF Airflow table back into the tune and then adjust it? If so - how?

Or am I missing something fundamental?

Thanks

Steve

[robison_02SS]

Thanks Gold.That helped alot.Ive used some of those controls just didnt notice it.

[5_Liter_Eater]

OK guys, here are some basics:

To tune the VE, disable the MAF by setting the MAF Fail High Freq to 0 and setting the P0103 DTC to MIL on first error and uncheck the SES Enable box.

Then reset your fuel trims via VCM Controls, Fuel and Spark, Reset fuel trims.

Drive/log and use the built in Histo to plot the LTFT against the VE table. To filter out any outlying data it may be a good idea to set the cell hit to at least 3. Also, if you enter PE the data is no good to you since fuel trims lock out in PE. To keep PE data out of the histo and getting averaged with all the other data you can log commanded EQ ratio and use the following plot filter "[PID.68]>1.0" or log commanded AFR Commanded (low or high res) and use this plot filter "[SENS.121]<14.6".

When you have your data copy the whole grid and paste special, multiply by % (not add) to the primary VE table. Look at the graph for any large spikes or dips or cliff transitions and hand smooth. If you have a secondary VE table copy and paste the appropriate rows from the primary VE to the secondary VE because the secondary VE is what is referenced when the MAF fails (if you have a secondary VE).

When you're happy with your fuel trims you can re-enable the MAF by setting the MAF Fail High Freq back to stock. Now it's important to note that once you enable the MAF the VE is only referenced during throttle transitions. Other than that the MAF is metering the air. So it is normal for your fuel trims to go out of whack again. Because the VE is not metering the air now, the MAF is. You can check this by logging the new 'air calc mode' PID. When it says low it's referencing the VE, when it says high it's using the MAF.

So now you need to tune the MAF the same way you tuned the VE so you need to make sure you're logging MAF Hz and set up a histo that plots LTFTs against the MAF table (one row) rather than the VE table. Once you have that log, flash, clear FT's, repeat until trims are back in line again.

Something else to consider is LTFTs are just a long term average of STFTs. I find it much easier to disable LTFTs, either in the tune or via VCM Controls, and tune off the STFTs using the same methodology.

Positive fuel trims mean that the PCM is having to add fuel above what the VE or MAF is calling for. So the VE or MAF is under-reporting the airflow; more air is coming on than is being reported to the PCM so the narrow band O2's show you're lean so the PCM adds fuel, thus the positive fuel trim. So lets say you have a +5 fuel trim in a cell, you multiply that cell by 105% (by pasting special, multiply by %) and the PCM now reports 5% more air coming in which "should" make the fuel trim go to zero. When you start getting close (within 1-2%), start multiplying by %-half to avoid overshooting.

Questions? Comments?

[rushhour]

5 Liter Eater

Thanks, I already see where I made an error by missing a step and the old write up I was using had add for the VE - so another mistake. And I did enter PE once - damn!

But I am learning with the help from this board.

Steve

[muayyadf1]

Questions? Comments?

Brilliant!

I have a Q regarding PE mode. If the RPM delay is set high will I enter PE mode if I'm on less than the specified RPM?

[5_Liter_Eater]

Not the delay RPM but the Enable RPM. I am not a proponent of altering PE to rxpand the range that you can tune with fuel trims. You're tuning for a situation that will not exist when you set the Enable RPM back and you're commanding stoich under load. Just accept the fact that you cannot tune PE cells with fuel trim tuning.

[rushhour]

Quick question - if we wanted to use the STFT's method for setting the VE, where is the box to disable LTFT's?

I have looked all over VCM editor and can't find an area to disable the LTFT's (nor in scanner). In the Fuel Control ->OL & CL tab, I just have the a column for Long Term Fuel Trims and under the heading it says LTFT Enable in words, no drop down box to disable. Below that is min & max ECT boxes to put in temp.

Sorry about the hassel.

Steve

[Rob]

Set the Min ECT to 284. Then LTFT's are disabled.

[rushhour]

Set the Min ECT to 284. Then LTFT's are disabled.

Rob - thanks

Steve

[5_Liter_Eater]

And in the scanner under VCM Controls, Fuel and Spark, Fuel Trim Learn = Off. I "believe" this should shut off LTFTs and leave STFTs enabled but you should verify that it doesn't whack them both.

On second thought it's better to just do it in the tune. That way you're sure what's going on.

[askipper]

How long should you drive after you reset your fuel trims before you start logging them in a histogram. I was loading my program,starting the car, opening up the scanner,DTC controls,resetting the trims-and immediately logging the histogram. Everytime I did this it would start out with like -16. I would drive the car like 50 miles each time. I did this like three times and every time it would start off showing -15 or -16 LTFT's.

[5_Liter_Eater]

As long as the motor is warmed up you should be able to start logging right away. Are you saying that it starts out at -15 and gradually averages out to less or does it stay around -15? I assume you're making changes inbetween?

[askipper]

As long as the motor is warmed up you should be able to start logging right away. Are you saying that it starts out at -15 and gradually averages out to less or does it stay around -15? I assume you're making changes inbetween?

Yes I am making changes in between to my Primary and Secondary VE. As soon as I load the new program and start the scanner I reset the trims and open the histogram it will go to logging high neg trims. If I drive around a bit before I open the histogram it will log trims around -1 to -8.I have tried tuning my VE's several times and it does this and throws me off. I always get scared and put my first tune back in-I don't want to blow my engine.