Tuning MAF at high RPM

[Nithros]

I don't have a wideband. I know I need one but as of now I'm using what I have.

I've tuned my VE table to 4000 RPM with the fuel trims (MAF fail set to 0 and PE off). Now I've reset my MAF fail to stock and disabled DFCO. I'm again using the fuel trims in a histogram vs. MAF output frequency.

Here lies the question - How high can I go (RPMs) in tuning the MAF this way and if not all the way - how do I tune for high RPMs?

I think the areas I've already dived into have been covered pretty well on this forum and others but I've read conflicting information and have a question in general about high RPM tuning the MAF and also problems running high RPMs/loads with PE off. I haven't touched OLFA.

[jimmyblue]

Why do you suspect the MAF needs tuning there?
That is the region where it should be at its best,
fidelity-wise.

[Nithros]

Thanks for your reply JimmyBlue. I guess I assumed that since it was off in other areas with the change in the intake, throttle body and headers - that it would also be off there and I don't want it to be seeing the wrong amount of air at higher RPMs and at WOT for sure. Would it not be? How high can I go in RPMs (4000 and above) before I stop checking?

I guess maybe I've answered my own question (at least as far as WOT goes) in that the fuel trims won't be used at WOT (except those left over from the MAF being off at the point I went WOT) so the only way possible is with a wideband... That still leaves the "how high should I go" question.

My assumptions are that I have the VE tuned SD to 4000 but when I plug the MAF in the fuel trims go positive meaning the MAF is not seeing all of the air which I sould think is normal since the engine is not stock. Naturally, I want to tune it a 4000 and below to mesh with the VE table. Also, my fuel trims above 4000 (when it's all MAF) so I want to tune those also. How high can I go?

[jimmyblue]

My opinion is, if the MAF plugged in jacks the fuel
trims but it's an unmolested stocker, you probably
have arrived at a speed density tune with the right
result, but maybe "two wrongs make a right" - like,
a fuel-side error pre-existing, which the VE table
revision has successfully compensated (as far as
fuel/air) but the actual airflow is different than modeled.

I'm not sure how you'd go about verifying it, that's
the real difficulty, absolute accuracy as opposed to
a relative balance. Seems like, you could get to a
sensible CylAir from first principles (cylinder volume,
MAP/IAT, assume some reasonable VE like 100% at
mid RPM WOT) and compare to the scanner CylAir
and MAF based CylAir (MAF airflow/RPM*???).
Somebody may have been through these calcs,
may be in the tuning spreadsheets or reworkable
from them, I don't know. But I think that's a missing
piece of the puzzle; like my grade school math
teachers used to harp on, you need a way to
check the work, to be confident in the answer.

Now, I've also seen anecdotes that 'vettes do not
tolerate MAF descreening well, that the curved duct
work may bias the airflow; though you may have a
stock Z06 MAF, changing the preceding tract (the
Vararam / power duct) could indeed introduce some
bias and require the MAF table to be reprofiled. Too,
if the Vararam is an oiled filter (?) type there might
be that hygeine problem with the MAF.

I think comparing the SD-mode airflow at MAP*RPM
(pick something like 5000 or so, nothing that challenges
the plumbing or pumping) to the MAF direct airflow and
the theoretical, might be enlightening; hopefully at
least you will get two of the three to agree well enough
to point the finger at the odd man out.

[Nithros]

I read your post and thanks again for taking the time to write that - there was a lot there but I still have the same basic question(s)... I still have the same questions. Don't people normally tune the VE to 4000 and then tune the MAF if they aren't going speed density? Up to how many RPMs would you tune the MAF?

[luv2spd]

ttt, curious on this as well.

[FlaBouy]

I read your post and thanks again for taking the time to write that - there was a lot there but I still have the same basic question(s)... I still have the same questions. Don't people normally tune the VE to 4000 and then tune the MAF if they aren't going speed density? Up to how many RPMs would you tune the MAF?

Don't quote me on this cause I am new too....... I am tuning through the VE tables myself and I have a wideband. I tuned VE up to 4000 or so and got everything like I wanted.. then I gradually increased rpms above 4000 over several logs and using the paste special command, I correct VE above 4000 with the logged histogram recording AFR Error %. It is best to do this in Open Loop (yes EC I learned something) and make sure the fuel trims and dfco is turned off. Seeing as fuel trims are off you need to be careful because if it is lean fuel trims won't be there to save you...... All of this is done with the MAF turned off. Then you go back to rescale the MAF to the VE you finished with. Again open loop to make sure the fuel trims are not playing games with you....

Somebody jump in and tell me that all this is right.......

Hope this helps.....

[Nithros]

I rescaled my MAF using the fuel trims above 4000 (PE and DFCO off).

Even with the way you proposed which is just a different method - same question - how high can you go safely?

[EC_Tune]

Without a wideband, you would be guessing at best. Just leave your PE fuel somewhere reasonable to start.

WS6FirebirdTA00 did some comparisons with MAF Frequency from run to run to see if he was achieving more airflow. Higher Hz = more flow no matter how the MAF is scaled.

EC

[silverTA2002]

I'd love to know how to calibrate the MAF above 4k rpms without a wideband. You definitely can't use fuel trims. And you can't use dynamic airflow (since you can't tune VE at full throttle without a wideband).

If you are off by 3% down low, should you go down 3% up top?

Should you just leave the MAF calibration to stock above 4k?

If after finishing with the MAF, you go to a dyno to accurately tune PE, does MAF tuning above 4k matter?

[luv2spd]

I'd love to know how to calibrate the MAF above 4k rpms without a wideband. You definitely can't use fuel trims. And you can't use dynamic airflow (since you can't tune VE at full throttle without a wideband).

If you are off by 3% down low, should you go down 3% up top?

Should you just leave the MAF calibration to stock above 4k?

If after finishing with the MAF, you go to a dyno to accurately tune PE, does MAF tuning above 4k matter?

I have been wondering this for some time as well. I've always just done a general scaling of the maf tables to get my trims slightly negative but then its not a perfect calibration.

[EC_Tune]

You should tune the MAF on the dyno (with a wideband) so that when you command an AFR, you get it (within reason) you will definitely tune the MAF above 4K RPM on the dyno.

EC

[Nithros]

I'd love to know how to calibrate the MAF above 4k rpms without a wideband. You definitely can't use fuel trims.

Although it's not the recommended or the best approach, you can tune the MAF above 4K with your fuel trims (if you don't have a wideband and this would be better than nothing at all). I think you were speaking of tuning your MAF at WOT which makes your statement true.

[EC_Tune]

Unfortunately, without feedback (wideband) you are guessing. I have seen 950mvdc o2 sensors produce a 13.0 AFR and an 820 mv o2 sensor produce a 12.5. Just not reliable for WOT in any way.

[silverTA2002]

So, when I (finally) get on a dyno.

Should I be changing the MAF calibration table to adjust WOT fueling......

Or, should I use the PE multiplier?

Based on what has been said so far, I would guess that you set the PE to what you want your (desired/commanded) A/F to be..... then adjust the MAF calibration until you reach that number.

But, if the end result is the same (actual A/F ratio), does it matter if you use MAF or PE?

I'd think PE adjustments would be WAY easier, since it's based on RPM, not MAF frequency. Making MAF adjustments, unfortunately, affects MANY different RPM and throttle positions. On a dyno, how would you know where to adjust if a specific RPM was too lean or rich?

[WS6 GreeN]

I know of people who just modify the PE table until they get the desired air/fuel but I like to set the PE table to where I want my commanded air/fuel to be, then adjust MAF accordingly. To answer your questoin about how to tweak a certain RPM, you could log maf hz and rpm and find that frequency range in the MAF table and tweak it that way. Just a thought!

[silverTA2002]

I know of people who just modify the PE table until they get the desired air/fuel but I like to set the PE table to where I want my commanded air/fuel to be, then adjust MAF accordingly. To answer your questoin about how to tweak a certain RPM, you could log maf hz and rpm and find that frequency range in the MAF table and tweak it that way. Just a thought!

That would probably work.

But, I'd imagine it would take more than a few dyno sessions to accomplish.

I think I've decided to go Mafless. After driving around today, I definitely have more power across the entire RPM range without the MAF.

I'm going to get my a/f consistent across the rpm ranges (based on my o2 readings) then it's off to the dyno!

If anything, since my VE table under 4k rpms should be just about dead on, my a/f should be pretty close to what's commanded (under 4k).

Couldn't I use the o2 readings down low and try to duplicate those readings above 4k to get a pretty close a/f ratio?

Down low, my commanded a/f is about 12.8, and my o2s are right around 900 (brand new bosch sensors).

[Russ K]

This is a scan from a 2002 Silverado. The wideband is in place of B2S1. Note that the B1S1 starts out at ~900mv and by 5600 rpm it is down to ~830mv.
The afr is a commanded/actual 13.0. The stock O2 mv is affected by temp and they just aren't accurate above or below ~14.7.

Russ Kemp

[VYSSWagon]

I did my tuning with NBO2's to 6500 RPM, using an AFR of 14.7:1, so I was targeting 450mV everywhere.

All the standard steps to tune to 4000, then:

In the "Dynamic Airflow" Tab set "High RPM Disable" to 6500 RPM.
I used my stock Low Octane Spark Table (10 deg. at 6000 RPM).

To begin with I did this in small steps (as it was a little scary!), but as long as you don't try to run too much spark I don't think it should be an issue.

Well it worked for me anyway, my STFTs are normally all 0 above 2000RPM and at WOT and + or - 3 below that (Top right corner).

[LSROVER]

OP, did you get an affirmative answer on this? I'm tuning my 5.3 truck right now and in the same boat. My thought is to tune VE up until 4k bc I plan on running the Maf still.

I dialed in the maf recording afr % error with a wideband while cruising on the highway trying to achieve steady state.

What is the technique to tune WOT with the maf?

Full throttle and record the afr% error? Multiply x % into the VE table?