What affect does disabling the MAF have?

[Nexus9]

I've made some modifications to my 2012 Grand Sport (long tube headers, 3" exhaust, ported throttle body, LS3 cam), so I took it to a local tuner, who made a lot of changes I wouldn't have thought of. I've learned a lot from his original tune, but a couple of things puzzle me. One thing I noticed was that the MAF was set to fail at 400 rpm [Engine/Airflow/Dynamic/High RPM Disable], basically disabling it from the system. When I asked the tuner about it, he said he applied a Speed Density tune - but oddly, there is no VE table (MAP vs RPM) in HP tuners for an LS3 that I'm aware of, and there were no changes in the Speed Density section [Engine/Airflow/Speed Density].
Anyway, LTFTs were averaging around +5%, so, having the time, tools, and inclination (but being too lazy to crawl under the car and install my WBO2), I decided to see how close I could get the LTFTs to zero. I manipulated the MAF curve, and sure enough, the LTFTs dropped into place, but now the car was running like crap. Sluggish, weak, bad idle, DTCs for the O2s and catalytics. Clearly, it was rich. This was odd to me - If I add fuel at the MAF curve, and the LTFTs STOP adding it, wouldn't the result be the same? So I went back the other direction, and sure enough, the car woke up again, (and the LTFTs came back up again) until I went too far, and the car was decidedly running too lean. Eventually, I found a sweet spot, and now the car is actually running better than when I first got it from the tuner (and has a slightly different MAF curve).
So here's my question - I was certainly changing the AFR using the MAF curve in HP Tuners, but the MAF function was disabled using the editor. LTFTs were responding proportionally, but they didn't actually seem to be compensating for anything or having any affect. When the MAF is disabled, does the VCU still process the fuel trims, but is not able to apply them? If the MAF is disabled, and there's no VE table, is the MAF table still the primary source of AFR?
Thanks for any insight.
Jon

[mowton]

Having not been a part of the conversation with your tuner, I don't understand what he may have been saying. To clarify your situation, the High RPM enable set to 400 does not disable the MAF, it sets the PCM into a MAF only airflow mode. This table is used to determine when the PCM will operate in what they call a "Blended mode" which is where the VE table is used to validate the airflow being recorded by the MAF and help "fill in" transient fueling events (quick stabs of the pedal, acceleration/deceleration etc.) where the MAF is slow to catch-up. The stock tune is usually 4000 rpm which says the PCM will operate in the MAF/VE blended mode up to 4000 rpm (non-steady state) and above that will go to MAF only (Steady State).

As far as the VE table, in 2006 or so, GM did away with the actual table and went to an equation based system whereas "coefficients" are developed which will define VE. This makes calculating the VE much simpler and precludes the need for memory starving 3 dimensional tables within the PCM. If you go to the Engine>Airflow>Dynamic (same place the High RPM Disable is, you will see the start of the coefficients with Zone RPM and MAP Boundaries. When you look at these two tables they define the overall "virtual table" that the VE will be divided into. Heading over to the Speed Density tab you will find the main VE Coefficient tables which the PCM uses to calculate in real time the VE value. As there is no physical VE table, you must use the Blue Cat VE Software to take these coefficients and develop a VE table which you can use to apply your error corrections to and then regenerates new coefficients which you them export into the tune file.

You can go to the Help section to read more on this and there are many other threads and internet articles on this subject.

The fact that you can alter the MAF curve and make changes to your trims actually contradicts the tuners allegation that it is in Speed Density?

Hope this helps.

Ed M

[Nexus9]

Ed,
Thank you so much for taking the time to write all this out. If I understand what you're saying, the stock GM coefficient tables are considered along with the MAF curve in calculating AFR up to 4,000 rpm; but since the volumetric efficiency of the engine has changed, but the coefficients have not, the tuner just eliminated the coefficient tables. So now the AFR is being controlled SOLELY by the MAF table (and enrichment tables). To do an actual Speed Density tune, the tuner would have needed to alter the coefficients using software such as Blue Cat VE, but instead, he just disabled them. I actually asked him if he used the BC software, and he said he had tried it out several years ago but "didn't like it". He also did NOT tune the MAF curve using the eddy current Mustang dyno in his shop, which was the main reason I brought the car to him - the car was only on the Dyno for WOT runs, which was $100 extra.

I have actually downloaded the Blue Cat software, but up to this point, didn't understand the value of it. First, I will need to learn how to use it. Then, if I imported updated coefficients, I could set the High RPM Disable back to 4,000 (Low RPM re-enable just slightly below that, 3900?), to use both MAF and VE coefficients, correct?

Any idea why the indicated fuel trims don't seem to actually have any effect?

Thank you for your time, Jon

[mowton]

Yes, you have the concept and the Blue Cat software is the only way to tune the VE for Speed Density, or even any changes like a cam where you are changing substantially the VE of the engine. The only other way is to install an HPTuners Custom Operating Systems which have the traditional VE tables. As far as the tuner.........I think I would look elsewhere or do like I did, take matters into your own hands :-)

Ed M

[Nexus9]

10-4, that always seems to work out best for us guys who just can't leave well enough alone. Thanks again for steering me in the right direction.

Go fast, take chances-

Jon

[Ranger6202]

If you don't like messing with the Virtual VE stuff or the Blue cat program, you can always do an OS enhancement and go back to a standard 3d VE table. I prefer it, but then again, everyone has their "tastes". I read not to long ago that the enhancements are free now. Might be worth trying.

[MikeOD]

Hey, I see that you're in Berlin CT...I live in Manchester. I'd be happy to help you with your car.

[BigDaddyCool]

Another 'Professional Tuning' job. I'd go as far to say that probably only like 10-20% of professional tuners in any country are any good, the rest are just rip off merchants who think they do a good job when really they just click a few buttons and hope it makes a difference.

There is ALOT to tuning a car, straight power runs on a dyno and lying to PCM's are BS ......... Atleast yours was like 5%....... my mafless tune was .......... bad. Made less power then standard, drove like utter crap.... all wrong...... Lean as F........ But yes as you said you do LEARN something from having your car tuned professionally.......

1. They know something........ as their is some madness to their methods.........
BUT 2. Its now time for you to fix their tune

[Nexus9]

If you don't like messing with the Virtual VE stuff or the Blue cat program, you can always do an OS enhancement and go back to a standard 3d VE table. I prefer it, but then again, everyone has their "tastes". I read not to long ago that the enhancements are free now. Might be worth trying.

Hey Ranger,

Thanks for the tip. Are you saying this is an HPTuners upgrade?

Jon

[Nexus9]

Hey, I see that you're in Berlin CT...I live in Manchester. I'd be happy to help you with your car.

Hi Mike, Thanks! I could definitely use some help with Blue Cat (I've downloaded it, created a VE table, and not really sure what data I use to modify it) or Ranger is suggesting an enhancement to HPTuners (I think). I'm familiar with the Volumetric Efficiency concept, as that was the primary method used in tuning my 2008 Harley Ultra when I put a cam in that - Would love to have a Speed Density tune on this car by the time we leave for Carlisle next Friday. My email is [email protected]. Would you be okay with shooting me a phone number and we could talk?

Thanks, Jon

[Nexus9]

Another 'Professional Tuning' job. I'd go as far to say that probably only like 10-20% of professional tuners in any country are any good, the rest are just rip off merchants who think they do a good job when really they just click a few buttons and hope it makes a difference.

There is ALOT to tuning a car, straight power runs on a dyno and lying to PCM's are BS ......... Atleast yours was like 5%....... my mafless tune was .......... bad. Made less power then standard, drove like utter crap.... all wrong...... Lean as F........ But yes as you said you do LEARN something from having your car tuned professionally.......

1. They know something........ as their is some madness to their methods.........
BUT 2. Its now time for you to fix their tune

I agree with you, Bud. If you've spent any time with any of Greg Banish's videos, you know that the best use of an eddy current dyno is the ability to tune the entire MAF curve cell by cell without racing down the highway and burning out your brakes. When I found out this tuner didn't even do that, it made me wonder how he arrived at the everything other than the WOT settings - LTFTs? Heck, I could've done that. I don't mind paying for education, but it cost me more than $700 to pick up that car, and I've done a lot of work on it since. The tuner is a nice guy, and I don't want to bash him, but I can honestly say I was a little disappointed.

[MikeOD]

Hi Mike, Thanks! I could definitely use some help with Blue Cat (I've downloaded it, created a VE table, and not really sure what data I use to modify it) or Ranger is suggesting an enhancement to HPTuners (I think). I'm familiar with the Volumetric Efficiency concept, as that was the primary method used in tuning my 2008 Harley Ultra when I put a cam in that - Would love to have a Speed Density tune on this car by the time we leave for Carlisle next Friday. My email is [email protected]. Would you be okay with shooting me a phone number and we could talk?

Thanks, Jon

I replied to your PM.

[Ranger6202]

@ Nexus9. Yeah the 1-3 bar enhancements under your OS tab. Do a quick read in the help menu about the enhancements. For the Gen iv's it gets rid of the VVE tables and makes one 3d VE table we're familiar to using on the gen iii's. It also ads a few other tables to help dial it in. Here's the link for the enhancements page http://www.hptuners.com/products/vcmsuite_enhance.php.

[HartRod]

A lot of good info here!

@ Nexus9. Yeah the 1-3 bar enhancements under your OS tab. Do a quick read in the help menu about the enhancements. For the Gen iv's it gets rid of the VVE tables and makes one 3d VE table we're familiar to using on the gen iii's. It also ads a few other tables to help dial it in. Here's the link for the enhancements page http://www.hptuners.com/products/vcmsuite_enhance.php.

If I read it correctly, it's not free, but costs 2 credits?

[68Camaro]

OS upgrades are free now. bout a month ago hptuners made all upgrades free. just make sure you update your software off of your customer login page and then upgrade away!

[Maxspeed96ct]

I'm another guy here from plainville ct , who did your tune if you don't mind me asking .

I couldn't realy get any positive reviews from local shops .
Let alone get anyone to do a speed density tune .

Long story short, I ended up doig my own sd tune but I'm on a e40 ecu so it was easier . But I may be able to help you out if you have any questions .