LTFT adjustment question V6 Astro

[FGCUhank]

I've read the doc and also found/like the Chevy High Performance article on the press release section and have a question on updataing the LTFT's.

I ran the scanner and my average number is -8. That Chevy doc says try to get +-5 so I am going to modify the MAF Airflow vs. Output table by .92 right??

Second question, a noob question I know, is why do you want to start off by modifying the LTFT trims as the computer covers it on the fly with the STFT's?

Thanks in advance.

[MMGT1]

Make small changes to your MAF scale. 2% at a time is the way I went. If you are tuning via narrow band I would not be aiming for 0 trims. Make sure you keep the trims in the neg. (- trims mean you are rich) Don't trust the NB's at all. Get it to about -3 to -5 and leave it at that until you can get a wide band in there.
And about the LTFT and STFT as to why....the less your car has to think about what it is doing, the more power you will make, and not just power, but EFFICIENT power. Not wasting fuel out the tail pipe and not so lean that you are damaging the motor. Tuning takes the guesswork out of the computer leaving you with a "finely tuned masterpiece"!!!! Now there is a lot more than fuel trims involved in tuning but it is a good starting point. While learning the trims and what is going on you will learn about MAF and MAP and how it is affected by timing, baro, fuel, elevation of the car, time of day, so on and so on..go here and start at the top. This write up kept me busy for quite a while.....

http://www.turbov6camaro.com/tune.htm

There is quite a bit of reading but this will explain a lot to you. It is headed as being for the 3800 but a lot of useful knowledge there.

[FGCUhank]

GREAT! Thanks for the feedback. Stuff is starting to make sense..

Yes, I guess that slighlty rich would be better than slightly lean.. Will start as you suggest and make small changes to get down to -3 to -5.

All the best.

[MMGT1]

Small changes are the way to go to try to avoid overshooting and going lean. Don't let it go lean.

[FGCUhank]

Well I think I made some progress here. I attached my scan logs from before and after. Thinking based on the second log of going down another 1%

I did see a couple of STFT's go positive a few times but this also occured with the factory program. Should I be worried? No pinging on the way home after changes.

I do see, even before when running the stock program that I have periods of KR. And on ocassion, before changing LTFT's I can pickup a slight ping during accell from cruise between 35-45. It almost feels like the TC is locked and the motor boggs. Once it kicks down the ping goes away. Guessing this will be something else I adjust once fuel trims are sorted out.

Also before going too much further should I look into a cooler T-stat?

All the best.
Hank

[MMGT1]

First offf, run your scan through your KR histogram and watch for MAX value. Remove that amount from your High Octane table under Spark Control. Eg:@ 1400rpm from 0.28g/cyl to 0.56 remove 1*. Then @ 2000rpm from 0.36 remove 3*, and from 0.40 remove 2* and so on until you see no KR in your scans.
This is another reason why you tune. You don't want any KR in your tune when you are done. KR means detonation, you want NONE!

Your MAF hz is not showing in the scan for me? Are you logging MAF hz in your table? You need the MAF hz to determine where to correct your fuel trims.

Trims are a bit better too. You are going the right way. Get it within -3%,don't let it go lean though

[FGCUhank]

Looks like we posted at the same time. I will go through your steps and post back.. Thanks

What I posted while you were typing is below
------------------------------------------------


I went down another 1% this am and noticed that in upper RPM's the ECM was adding fuel. Numbers were +1. But down at the low end and especially during idle I am seeing numbers in the -5 to -9 range.

Should I open up the table again and rather than making global adjustments?
Looking at the LTFT histogram from the attached log I was thinking of going down another 1% at the first part of the MAF Airflow vs. Output table, leaving the middle alone and going up 1% near the end to get rid of the positive numbers on hard accell. Question is how does the MAF Airflow table tie to RPM's? I see it uses frequency, at first I thought it was RPM's



Also I have to do something about the air intake and the IAT's I put the factory intake tube back in but noticed that even it sits about 4" behind and to the left of the radiator. Unless I am at speed it is sucking air out of the engine compartment. It is amazing how hot the van engine compartments are.

[FGCUhank]

I'm having a tough time finding where to log the MAF hertz, can you point me that way?

Thanks

[MMGT1]

Go to Table view in the scanner. Right click on table. Click insert. Your PID list will open. Expand Engine tab, then Air Flow. Under Air Flow you will see Mass Air Flow (Hz). Double click on it and it will now be in your table to view in your scans.

Then go to your chart view and right click on it. Chart settings, then add the PID for MAF Hz there as well. You will now be able to view your MAF in the table and chart!

Save the Config as whatever you want. Then you have it and won't loose your changes.

[MMGT1]

Once you are logging Hz this will all make sense. Get another scan with the MAF hz added and post it up

[FGCUhank]

Will do, I really appreciate all your feedback and help.

[MMGT1]

Did installing the MAF hz work for you? Does it show in your table now? Not asking for a scan, just seeing if it worked for you....

[xonelith]

Keep in mind, the wb will tell you if you are rich or lean, not the LTFT/STFT. They just tell you what the narrowband sensor is guessing (averaging) because the narrowband sensor is only accurate at stoich. If it's negative, it's pulling fuel and conversely adding fuel when positive (based on NB readings). So, you really aren't rich or lean as the computer is compensating to get you to stoich. Only the wideband can tell you if you are rich or lean (someone will correct me if i'm off base here)

Read the post by Russ that describes disconnecting your NB sensor to tune your MAF (and VE's). Correcting things while you aren't in PE, becomes time consuming and innacurate if not done correctly.

[FGCUhank]

Will have to set it up at the end of the day. They actually expect me to work full time when I am not in class... Can you believe that... gosh...

[MMGT1]

Yea Xon, I believe for now he is on NB's only. I have said the same thing to him before about the WB. Most of what is here will get him ready for the wideband when he gets it in....
Figured helping now would help to get ready to understand the MAF to AFR relations, then it will be easy for him when the WB is installed

Place this link in your fovourites...don't loose it.

http://www.hptuners.com/forum/showthread.php?t=8815

Once you have your WB follow this post to the tee. It works!!

[FGCUhank]

Awesome, thanks guys... Still at work, will get the scanner reconfiged as you asked and post up a scan later tonight.

Ok, forgive me, point me at the post that says what a wideband is.... Sorry, noob...

[FGCUhank]

Let me clarifiy again, do I really want/need a wideband for a V6 astro? You guys are really pulling more HP and speed than I ever will.

[MMGT1]

http://www.bmotorsports.com/shop/pro...roducts_id/357

This is a wide band. You need one to be able to read the "Actual" air fuel ratio your van is producing. What you see in your scans now is what is called a "narrow band". These are not accurate at all! You are tuning NB right now and this, as Tim said, is just a guess. I had seen in a post before that a WB was brought up, sorry I didn't know that you really didn't know about them!! This is the best investment you can get to tune your van bud. As soon as you can, get one!! I can help direct you on the install as well.

A wide band is not about power and speed per say, it's about having your trims RIGHT! No guessing involved

[FGCUhank]

Here are two quick scans from yesterday. I have not had a chance to look through them yet, think it is a wife, kids and full moon thing this weekend.

Long story on why the vacuum gauge is there...

Am I going to be able to make some progress on tuning without the wideband? I have about 1000.00 in software and hardware for this class that the Univ. won't cover.

I also am guessing I need to do something about the IAT's. Even the factory air intake for the van is inside the engine compartment. Driving in traffic and slow streets it looks like I am sucking in engine compartment air.

Also what about a cooler t-stat?

All the best.
Hank

[Russ K]

A 160* stat would be a good plan. You should also log commanded afr, looks like your PE is delayed. Set the PE delay rpm to 0, and the enrichment rate to at least 2 (some cals allow 4). your LTFT's are close, looking at the maf histogram.

You can remove the right air cleaner snorkel, and the left side air cleaner box silencer for more airflow. These plastic pieces can be removed by prying them out with a screw driver.

Russ Kemp