question on maft settings, and autotap o2, a/f readings

[Magnus]

The PCM will learn your base values.. however at WOT the frequencies are higher and 5% of a big number is more than 5% of a small number. [img]smile.gif[/img]

So the PCM will learn the changes for cruise and mild MAF #'s somewhat accurately, however as MAF values go up, the change also goes up.. but LT's don't get corrected so you are forced to live with the change.

0 base setting. Use it, its your friend. ;)

Does this clarify any better?

Also, if your not convinced... do this..
Log Engine RPM, MAF flow rate, B1S1 O2, B2S1 O2

Log them with NO MAFT do some WOT runs.
Add the MAFT on a -5% base 0 WOT. Give the car 15 miles of cruise (varry TPS) to learn, then log again.

Then do the same for -10% base and -15% base... and then +5 and +10 bases as well...

You might be a little more convinced. [img]smile.gif[/img]

[John_D.]

Alright dang it, you win... [img]smile.gif[/img] I still don't understand it, but I can't argue with the numbers.

The ltrim is the average at other than idle and WOT.
The first MAF (MAFI) column is idle.
The second MAF (MAF12) column is the range in 1st and 2nd at WOT as it went through the rpms.
The third MAF (MAF3) column is in 3rd as it hit 100mph at WOT.

Base Ltrm MAFI MAF12 MAF3 .o2.
==== ==== ==== ===== ==== ====
+00 -10.1 0.64 17-22 19.5 .946
-05 -04.9 0.59 14-21 18.8 .940
-10 -04.6 0.51 14-20 17.4 .917

I didn't quite get 15 miles between runs though...

Found out that the car takes 13-14 seconds to go 60-100. That needs to change if I'm going to hit 100 in the quarter!

[Magnus]

Here's a question.. why are your LT's at -10?

Did you touch your stock TB/MAF setup at all?

[John_D.]

Well, I did touch it once...

Seriously though, not yet. Removing that excess post in there is a possibility down the road, probably no porting or polishing though.

I put on a K&N, broke the fins out of the lid, trimmed some of the divider in the middle of the outlet of the lid, opened up the bottom of the box, and raised the base a little bit. And the free ram air thing.

Haven't removed the silencer or changed the tubing.

Screen is still in.

Maybe the headers and 3" exhaust have some impact?

[ June 04, 2002: Message edited by: John_D. ]</p>

[John_D.]

Magnus, it finally clicked this morning!!!!

I got off in the weeds when I started thinking ltrims only, and forgot about the maf reading itself, and how much each of these is weighted...

Ltrims are probably not weighted as heavily in WOT mode, as the maf reading. So now it makes sense that telling the pcm there is less air would lean out the WOT mixture, since the ltrim correction is only a minor variable.

Especially if the ltrim crosses over zero and goes positive. (which is what autotap reports usually at WOT).

[Magnus]

lololol...

your LT's go how positive at WOT.. At WOT is the ONLY time you should really pay attention to your LT's.. cruise is worthless imho..

What are your LT's at WOT??

Actuall, the LT is a HUGE factor .. its the calculated offset that the MAF #'s must be factored by to achieve the correct air/fuel ratio.

I have NO clue what my LT's are at cruise.. just -14% at WOT.

Also.. short term FT's are worthless to us as well. don't look at those either.

If you look at my above examples, without the LT correction factor the air/fuel would be inaccurate at WOT. The PCM needs both the MAF reading AND the LT calibration to achieve the desired air/fuel ratio.

[John_D.]

I've been surprised at how fast the lt's change. Since they are supposedly "long term" values I thought they would change more slowly, but I can watch them change practically every second going down the road.

There may be different lt's for different cells, I haven't checked that yet, so some of the flipping around may be as the pcm moves through the 0-4 fuel cells.

They run around +2, +3 at WOT and don't change during the WOT time. Even if they were negative right before that. They will typically go to that value a couple of records before the tps hits 100%, usually by 85%, and will hold there for a couple of records after the tps drops back down.

The v8 guys' documentation says the ltrims are not used at WOT... Or are barely a factor. Depending on who you listen to.

(oh, and who were you talking about, regarding the second set of egr block-off plates? I still haven't figured that one out...)

[ June 05, 2002: Message edited by: John_D. ]</p>

[Magnus]

The second set of EGR blockoff plates will remain a mystery... like the sith lord... always 2 there are.. he is out there.. ;)

+2-3 LT's are NORMAL at WOT.. you car is fine. [img]smile.gif[/img]

And don't listen to those V8 guys who say the LT's aren't used... If you could manually change your LT's at WOT, you would notice the air/fuel ratio change with them if the MAF freq stayed constant.

I consider myself a tuning expert. I know whats up. [img]smile.gif[/img]

Also, LT's don't change during WOT because the PCM stops using the O2's for readings... LT's change at cruise because the PCM uses the o2's to see how far it needs to adjust.

LT's are long term yes, but they do learn very quickly.

Another example....
Say RPM and MAF flow remain constant
20lb/min and 5000 RPM's....
lets look at how the LT's effect the O2's..

You say you have a +2 LT... so we can use that as your medium calibration

LT - O2

+7 .915
+6 .910
+5 .905
+4 .900
+3 .895
+2 .890
+1 .885
+0 .880
-1 .875
-2 .870
-3 .865
-4 .860

Now, thats saying you are WOT.. at 5000 RPM's and air flow remains constant... the PCM is in open loop mode and is NOT using the o2's so the LT's will not be learned out.... and if you MANUALLY change the LT's (if you actually could).. thats how your o2's would be affected.

Follow?

This is another reason why you can use the WOT setting on the MAFT to actually change the o2's at WOT only... you see, once you enter WOT, the car stops using the O2's to calibrate, and uses the MAF reading and the LT calibration factor to determine pulse width.. if you decrease the MAF reading, the PCM will not know because it's ignoring the O2's and will just use the associated LT and generate a leaner or richer mixture based on how much you changed the MAF value.

- Keith

[John_D.]

I'm with you on the interactions of everything. [img]smile.gif[/img]

I had just taken the approach of getting the reported air flow value "corrected" across the board. And then I shouldn't need to fool the WOT. Correcting it, meaning if the ltrims approach zero, then the air flow must be getting reported accurately. And if the reported air flow is accurate, then the pcm would be able to do it's job on the a/f ratio at any rpm or throttle setting...

But there are too many variables I think.

So the "simpler is better" approach takes me back around to tweaking the WOT setting only.

I still wonder, if the reported air flow is off by some percentage, then it will be off by a larger amount at WOT, but the ltrims would have been generated while it was off by a lesser amount while running primarily at part-throttle.

But the ltrims are a percentage too, so it should still extrapolate out correctly.

Although I have to say, taking the base to -10 and WOT to 0, has worked out pretty good for the past 50 miles of interstate driving. I run about a .88 o2 at WOT under various load conditions with that combination.

I figure this tuning exercise is not done though... Just trying and learning at this point.

[Magnus]

sweet..

Now to confuse you a little more... the LT is actually the calibration for the air/fuel ratio...

It could be off because your MAF values are incorrect, your fuel pressure is too high/low, you have a leaky injector, too much back pressure,... anything that can off set the air/fuel ratio your LT's make up for.

If your MAF reads 100% accurately, then its most likely the effeciency of your engine that has changed which is why your LT's are off.. but yours are very close to zero anyway.

However when you change your MAF setup like several of us have, the correction is done with the LT's. [img]smile.gif[/img]

LT's are so very important. Without them everything would have to act like stock in your car to achieve decent air/fuel ratio.. change one thing and you will be far off..

LT's are the correction factor.

And the PCM is smart enough to make the right correction at WOT based on what it learns from the cruise readings. [img]smile.gif[/img]

[John_D.]

I am curious why I was getting the -7 to -10 cruise ltrims before the maft.

I believe the wot ltrims were +3.1 before the maft. The wot's haven't changed much, just the cruise ltrims.

I always wonder how far off the o2 sensors drift as they accumulate mileage. Hopefully they stay fairly accurate and die suddenly, instead of drifting off and getting all the other settings off before they go...

Did you look into this issue with the voltage problem with the maft units?
http://www.vetteguru.com/mods/maf/
Just curious if you ran into this, and what you think about modding the maft itself.

[Magnus]

I believe ramchargers has fixed the voltage issue with the units.

[DominusEtDeusNatus]

How can something so simple get so complicated.


1. LTrims Mean Nothing At WOT. Get your LTrims as close to 0 as possible using a MAFT.

2. Get your LTrims from fuel cells 1-19, take a average of these readings. Negative number means rich, positive means lean. Adjust your MAFT BASE for either a rich or a lean condition. Get your LTrims are as close to 0 as you can get them with little to no knock. Around +3 should be fine.

3. When changing values on the BASE setting of the translator you are changing the signal across the whole range. WOT settings fine tune just WOT on top of your BASE settings.

4. Now you want to get 02's that fall in fuel cell 22 with throttle at a 100%. Once again, get the average. The ideal range for these are .89 - .91, anything above .91 is rich and anything below .89 is lean. Adjust the WOT setting until your 02's read between .89-.91 and you have little to no knock. Adjust to negative if you're rich, positive if lean.

Facts:

The PCM will not "learn out" the settings of the MAFT on the BASE. What will happen however is a permanent change in Long Term Fuel Trims. This will most directly effect perceived engine load and timing. Remember that no matter what, the O2 sensors rule in 'closed loop' mode, and will always tell the PCM to adjust to 14.7 stociometric a/f ratio. The MAFT setting during fuel enrichment (WOT) however will always be permanent since the PCM freezes any possibility of updating its fuel trims or any other values. In this mode the PCM solely relies on raw flow data from the MAF, RPM, and TPS. This is what makes the MAFT a very good product.

Source: Shawn Whitehead on corvette forum and LS1Tech.

[John_D.]

Dom - you're right, it did get very complicated. I started out with the exact same info you just shared, and that's part of why it got so complicated. That info is not quite right for the v6 cars.

We don't even have fuel cells 1-19 for starters... Or fuel cells 20, 21, or 22 for that matter. We don't even have one single fuel cell dedicated to wot operation. And the mantra about "ltrims mean nothing at wot" also does not apply.

So it's definitely been learn as I go, on this one, with just a tidbit here and there to help point me in the right direction.

[Magnus]

<blockquote>quote:</font><hr>Originally posted by Dom:
1. LTrims Mean Nothing At WOT. Get your LTrims as close to 0 as possible using a MAFT.
Your WOT LT is the calculated offset from stock type conditions. It does mean something. And no you don't have to get it as close to zero as possible. I ran 14.0 stock heads/cam with them at -12%.

Don't believe the common misbeliefs about LT's.. a LOT of what others think about LT's is false.. I have read it all, and then I did my homework. People believe zero is the way to go because the PCM has to do less calculations... well perhaps if they had a 1mhz PCM they should worry, but our PCMS can do it instantly, thank you come again.

2. Get your LTrims from fuel cells 1-19, take a average of these readings. Negative number means rich, positive means lean. Adjust your MAFT BASE for either a rich or a lean condition. Get your LTrims are as close to 0 as you can get them with little to no knock. Around +3 should be fine.
Blah

3. When changing values on the BASE setting of the translator you are changing the signal across the whole range. WOT settings fine tune just WOT on top of your BASE settings.
If you want to get technical, the WOT setting actually kicks in at a certain frequency. ;)

4. Now you want to get 02's that fall in fuel cell 22 with throttle at a 100%. Once again, get the average. The ideal range for these are .89 - .91, anything above .91 is rich and anything below .89 is lean. Adjust the WOT setting until your 02's read between .89-.91 and you have little to no knock. Adjust to negative if you're rich, positive if lean.
Well, if your volumetric effeciency changes, you will make more power at a different O2. More effecient cars (heads/cam/intake/exhaust) that are NA can make more power with a leaner mixture safely.


Facts:

The PCM will not "learn out" the settings of the MAFT on the BASE. What will happen however is a permanent change in Long Term Fuel Trims. This will most directly effect perceived engine load and timing. Remember that no matter what, the O2 sensors rule in 'closed loop' mode, and will always tell the PCM to adjust to 14.7 stociometric a/f ratio. The MAFT setting during fuel enrichment (WOT) however will always be permanent since the PCM freezes any possibility of updating its fuel trims or any other values. In this mode the PCM solely relies on raw flow data from the MAF, RPM, and TPS. This is what makes the MAFT a very good product.

Yea, umm.. the adjustment of the LT's by the PCM can be considered as learning it out.

I completely agree with the rest of his statement.
<hr></blockquote>

Dom, I read all their articles.. ALL of them.. and began to ask them WHY.. WHY certain things are the way they think they are... most were unable to answer..

The biggest reason I got for 0 LT's was so the PCM would have to make less changes.. But of course, those people had computers that were running with vacuum tubes and not circuits like us.

However, I didn't want to get THIS technical about it but yes the PCM does use the MAF values to percieve engine load and does change timing. Ours seems to work a little differently than the LS1's though.

LS1's have more timing with less load, we have more timing with more load... or to put it another way... LS1's decrease their maf readings to achieve more timing, we can increase ours.


And to get even more technical about it.. the MAF sensor's readings are not linear.. its actuall curved... yet the MAFT adjustments are done on a linear scale... which is one of the main reasons why I strongly urge ANYONE to keep their base settings at zero.. unless you have driveablity issues..

Let the MAF/PCM learn the setup with NO interferance and fine tune the sucker with the WOT settings. [img]smile.gif[/img]

As John now knows, his o2's are MUCH more consistant with a zero base setting than they were when he had a -5 and -10% base.

Have a nice day. :D

- Keith