RWTD - I took your suggestion on MAF only CL

[5_Liter_Eater]

VE tuning on gen 3's is so easy the benefit is debatable, especially with a big cam. Gen 4's with their virtual VE tables are not as straight forward and the benefit of pure MAF is greater. For the record I ran pure MAF pre-blower when I had a 238/242 .605/.610 on 112. Not the biggest but some decent overlap there and it ran fine MAF only.

[5_Liter_Eater]

Yes you are correct.. and thank you for being patient..

I am JUST getting back into the tuning game after 5 years.. I know I sound like a dumbass newb.. But I Swear to god.. I used to help others tuning with the MAF Translator and logging with Autotap, then on to LS1edit.. Etc..

Anyway.. I promise to listen and learn...

So once the VE is disabled what is the next step in tuning? What am I logging at that point and what trends am I looking for? By the way.. I am in FL with the worst air in the country.. Does this still make sense to disable the VE?

Assuming you fixed your IFR table (you did fix it right? ) then you start logging either AFR error (with a wide band) or fuel trims and use the MAF histogram to plot the error against the MAF table. then you just copy and paste special (multiply by %) the error you get directly onto the MAF table. Best to start a new thread on this as there are other nuances to discuss.

[Matt-B]

One question I have about giving the MAF 100% control by setting the "High RPM Disable" table to 0 is whether or not it disables the 'pump shot' transient fuel function, which is normally controlled at least in part by the VE table. I suppose one could do a WB log to investigate.

Setting the "High RPM Disable" table to 0 sure seems to be the best way to tune the MAF.

[5_Liter_Eater]

It should definitely be part of a routine for tuning the MAF so you're ensured that the VE is not being referenced although I haven't seen it in any write ups.

Not sure about the pump shot thing.

[jtaliaferro]

I'm glad it's working for you well (I wish more would try this). The MAF is always going to be accurate (once it's tuned in properly), whereas the VE can alter based on weather/conditions. Sure, there are correction parameters for VE for these variable conditions, but it's not the easiest to master without GM's equipment and testing methods.

+1

I have been very very happy with my tune since I have enabled the MAF again.

+1
On the idle statement!

[playtoy_18]

Seriously tho, a MAF failing is about the same chances as gettings truck by lightning.

Actually,in the past 2 1/2 years as a Ford tech i've encountered 1 failed MAF and 2 trucks struck by lightening....
So you might have a better chance with the lightening

[mowton]

What Matt is referring to is the transient fueling requirements. The MAF is a device which provides air mass values that are is used in part by the PCM to calculate the cylinder charge. Based on this charge, the PCM fires the injectors long enough to reach the commanded AFR. You are assuming that all the air moving by the MAF will be included as the volume of cylinder charge. This is only true in a steady state condition. When you stab or let up on the pedal, the there is a instaneous change in Manifold presuure. This renders the MAF input to the fueling equation inaccurate because some of the air mass is actually "filling" the void in the intake manifold due to pressure drop or "stored" pressure in the manifold is adding to the charge which had already been measured. The VE is a value which the PCM looks at first and bangs it agains the MAF readings. If a large disparage, the VE value is used until the MAF operation settles out.

That is why the Maf and VE work in concert. Without it you will end up with lean/rich spikes which could be damaging to the engine.

That is my understanding, your mileage may vary......

[69lt1bird]

That is why the Maf and VE work in concert. Without it you will end up with lean/rich spikes which could be damaging to the engine.

That is my understanding, your mileage may vary......

If that was true, how do you explain the thousands of people running in speed density mode. The MAF only variation is just the same thing but using the MAFinstead of a VE table that is only accurate for the day/temp/barometric pressure that you tuned it on.

There are still other tables that have an effect on other aspects of the tune other than the VE table.

[Gh0st]

If that was true, how do you explain the thousands of people running in speed density mode. The MAF only variation is just the same thing but using the MAFinstead of a VE table that is only accurate for the day/temp/barometric pressure that you tuned it on.

There are still other tables that have an effect on other aspects of the tune other than the VE table.

No. Running MAF only is not the same as SD. There's a common misconception that GM computer will completely ignore the VE table when set to "MAF Only".

[69lt1bird]

OK, I am open to a better explanation from someone who knows.

[KLUG'S SS]

OK, I am open to a better explanation from someone who knows.

Me too

[Eagle]

W...the Maf and VE work in concert. Without it you will end up with lean/rich spikes which could be damaging to the engine.

That is my understanding, your mileage may vary......

This is also my understanding. Sd tunes exist because quite a few tuners seem to rush through their tunes and push owners to go SD because its easier and takes less time to get perfect... I've seen it done. Granted there are reasons to go SD, but on a car that is mostly street driven, going SD isn't the right way to do things, IMO.

OK, I am open to a better explanation from someone who knows.

I'm interested in hearing about how the GM PCM still references the VE table while set to "MAF only" mode. Very interesting. Thanks, Ghost!

[5_Liter_Eater]

I'm interested in hearing about how the GM PCM still references the VE table while set to "MAF only" mode. Very interesting. Thanks, Ghost!

Too bad this isnt the 4th gen forum because there is a new PID called air calc mode that tells you whether the PCM is referencing the VE or MAF at any given time.

[Eagle]

How very true. I can't wait to get my hands around my buddies 09 G8 GT... should be quite the experience. He'll be my first 4th gen tune...

[eficalibrator]

No. Running MAF only is not the same as SD. There's a common misconception that GM computer will completely ignore the VE table when set to "MAF Only".

OK, I am open to a better explanation from someone who knows.

It is my understanding that going to "high speed" mode uses the filter MAF exclusively for airflow estimation, per the calibration note in the software.

Remember that during a transient, you still have wall film corrections that are looking at fuel to wall impact and evap factors that will definitely be in flux. If you change the injector targetting or port geometry, expect these to need a little work to perfect.

[My90Iroc]

Sd tunes exist because quite a few tuners seem to rush through their tunes and push owners to go SD because its easier and takes less time to get perfect...

Easier and less time???? I don't believe I agree with that but that's a different discussion.

I have nothing against maf only or sd but can't the same arguments be made against maf only that are made against sd? That all the bases aren't covered? I understand the arguments for as well but I think the 2 systems work best hand in hand.

I guess one of my questions are what experiences are some of you having that are leading to want to run maf only?

[Arcolog]

I just did this the other day and well, I have a pretty stout cam, and at idle the frequency sits at 3500hz the entire time. Doesn't act funny at all, I am actually rather suprised.

Cam is 248/254 (25 degrees overlap)

Seems to run good so far, barely made any adjustments so far, need to finish, but got to busy putting my clutch master cylinder in and adjusting it.

Oh and it was 90 degrees today with high humidity and last night it was 60 with lower humidity and it ran the same no matter the weather condition, and a crap load faster than trying to hit all the cells on a VE table.

[mowton]

I just did this the other day and well, I have a pretty stout cam, and at idle the frequency sits at 3500hz the entire time. Doesn't act funny at all, I am actually rather suprised.

Cam is 248/254 (25 degrees overlap)

Seems to run good so far, barely made any adjustments so far, need to finish, but got to busy putting my clutch master cylinder in and adjusting it.

Oh and it was 90 degrees today with high humidity and last night it was 60 with lower humidity and it ran the same no matter the weather condition, and a crap load faster than trying to hit all the cells on a VE table.

idle is steady state and there are a bunch of other "helpers" keeping the idle right like LTIT/STIT, under/over speed timing, a dedicated table for timing values and most important Adaptive Idle startegies. You still have the transients or dynamic issues associated with MAF only as far as I have learned, but again that is just my experience (over/under fueling transients via STFT logging), understanding (readings) and opinion.

I would like to see someone with a wideband run some logs with some agressive driving (just short of PE) and post their results. The VE tuning up to 4000 rpm is pretty easy as the affects are more affected RPM so you could take the % delta of the cells you hit the most in a given rpm column and use it on all the other cells to get close. Of course this only works if you are starting from a stock table. It also helps to find a hill to assist in hitting as many cells as possible for us not so fortunate to own a load dyno.

Thanks

Ed M

[BTLD_LS1]

very interesting discussion. I might have to give this a shot if i go to the track next weekend...

Seeing as I probably have one of the largest cams, 258/270 @ .050, in a baby motor, 347, it should be a good test

[Ryan L]

Mustangs use a only a MAF (switched from speed density ~20 years ago) while Honda used only speed density until a few years ago. How unsafe can it really be to run only a MAF?