MAF Tuning - Hope 5_liter_eater chimes in

[ktoonsez]

Went and finally turned my MAF back on yesterday on my LS3 and was going to do some MAF tuning based on the comments people are now making about VE tuning vs. MAF with the LS3, what a mess. This is the first time I have turned the MAF back on sense I started the VE tuning after my mods (moderate CAM, CAI and Kooks header and x-pipe). Get so many logged Misfires HP can't even keep up with them. Either my MAF is broken (MAF seams OK though looking at the Hz in the scanner table) or I am not modifying the right table (table MAF airflow vs. output frequency) because no matter what adjustments I make it always is misfiring to death with the MAF on. I log the STFT vs. MAF and paste special multiply % to the table "MAF airflow vs. output frequency". Just don't know. Anyone have a clue, 5_liter_eater?

[5_Liter_Eater]

I've never seen that before. I guess it's running real rough and the misfires are real? Or is it running OK but HPT is logging misfires for an unknown reason? Is your MAF table stock? You have LTFTs disabled right? What are your fuel trims saying; extremely positive?

[Spectre]

What if you have turned on in the tune but unplugged, or unplug it while it's misfiring...?

[ktoonsez]

5_liter_eater:

1. 80% or so of the misfires I can not feel, just increments "Total Misfires" in the table in the scanner.
2. The other 20% that is really noticable is at 1 to 10 miles per hour, the car is running pretty rough.
3. "Total Misfires" only get incremented with MAF enabled (when I say that I am talking about setting "MAF Fail High" to 0 hz to disable and 14500 to enable, not unplugging it).
4. I have been logging the STFT vs. MAF and paste special multiply % to the table "MAF airflow vs. output frequency".
5. LTFT is disabled.
6. Fuel trims are as high as 21% negative, doing the paste special on the MAF table has no effect on it.

Spectre:
Can't unplug the MAF, the IAT sensor is built in on the LS3. I think you can do some hot-wiring to pull it off but I know the software switch works due to this problem only occuring when "MAF Fail High" is set 14500hz vs. 0hz.

[Spectre]

Oh yeah, I forgot. I rewired mine to be separate.

[ktoonsez]

One more thing I noticed to 5_Liter_Eater is that logging "Air calc mode" mine never says "Low", I have seen 3 different values with MAF on or off.

1. Normal - MAF was OFF
2. Normal pnt - MAF was OFF
3. High Speed - MAF ON

Where your comments in that one thread about VE vs. MAF tuning on a different vehicle than an LS3?

[ktoonsez]

Here is another observation I had after about an hour of logging with MAF enabled and VE enabled (still have the misfire problem with both on). The "Air calc mode" always stays at "Normal" when idling, cruising with foot off of the gas and WOT until 4000 RPM just like the setting I have set. After 4000 RPM the "Air calc mode" switches to "High Speed" and back to "Normal" after getting below or releasing the gas pedal.

So in conclusion, I am not seeing what some are seeing. My "Air calc mode" is almost always reading "Normal" (VE calcs) and only "High Speed" after 4000 RPM. I am wondering what car these people were tuning? Also wish I could figure out why the misfires are happening with MAF enabled? Another observation the misfires are 3 times worse with MAF and VE enabled over just MAF enabled alone. Wierd.

[EC_Tune]

VE is always enabled. You can't completely disable it, just make it less intrusive.

What is your fueling doing with the MAF enabled? Sounds like the MAF tune needs help there. One quick check is to compare the VE Airflow with the MAF airflow. Where they are divergent that is where the MAF needs help.

[ktoonsez]

VE is always enabled. You can't completely disable it, just make it less intrusive.

What is your fueling doing with the MAF enabled? Sounds like the MAF tune needs help there. One quick check is to compare the VE Airflow with the MAF airflow. Where they are divergent that is where the MAF needs help.

MAF tune is all good now. To do the tuning for the MAF I followed another threads suggestions turning the VE "High RPM Disable" to 100 and VE "High RPM Re-enable" to 0 and did some logging with STFT vs. maf, did the paste special multiply % on the MAF table. All STFT vs. MAF fields in the log are now between +/-2.

Still getting lots of "Total Misfire" counts with the MAF table all tuned in and of course they all go away when I disable the MAF, setting "MAF Fail High" to 0. All the misfires are at low rpm's and mostly when my foot is OFF the gas completely, maybe one out of 10 times if I touch the gas a little bit I'll get some misfires but most of them are zero gas. It can get especially bad when just sitting there in park/neutral as well, most of the time when I turn on the car as soon as the startup delay's for STFT are done and the STFT's kick in the "Total Misfires" number will go from zero to 34, I have seen as high 84.

What would I log to compare "VE Airflow with the MAF airflow", I'm not quite clear on what you want to compare?

[EC_Tune]

First and most important: What mods are there on your Vette?
Second you need to be logging VE Airflow as well as MAF Airflow to see the diffferences. If you wish you can make a custom pid that gives you a % differential from MAF to VE airflow. Most work well with % differences rather than first differences. Use the AFR Error% custom PID as as go by to set up your custom PID.

[5_Liter_Eater]

One more thing I noticed to 5_Liter_Eater is that logging "Air calc mode" mine never says "Low", I have seen 3 different values with MAF on or off.

1. Normal - MAF was OFF
2. Normal pnt - MAF was OFF
3. High Speed - MAF ON

Where your comments in that one thread about VE vs. MAF tuning on a different vehicle than an LS3?

This may be specific to the LS3. IIR when I log it it only ever says Low and High. I'm not sure what Normal pnt is. In any case, if you set the dynamic airflow disable RPM to below the idle speed the air calc mode will always read high speed and the VE calcs will be ignored. That doesnt help your misfire problem though. Could be K&N oil on the MAF wires. May want to try taking it out and cleaning it (with MAF cleaner, yes, they actually have that).

[5_Liter_Eater]

What is your fueling doing with the MAF enabled? Sounds like the MAF tune needs help there. One quick check is to compare the VE Airflow with the MAF airflow. Where they are divergent that is where the MAF needs help.

This is a great idea Doug. I run with the dyn airflow calcs disabled (MAF only) and it runs fine, I could use this method to derive my VE table.

[ktoonsez]

First and most important: What mods are there on your Vette?
Second you need to be logging VE Airflow as well as MAF Airflow to see the diffferences. If you wish you can make a custom pid that gives you a % differential from MAF to VE airflow. Most work well with % differences rather than first differences. Use the AFR Error% custom PID as as go by to set up your custom PID.

EC_Tune:

Here are the mods on the car:

K&N CAI
Kooks Headers and X-pipe
CAM is 224/228 .580 lift 114 LSA

I thought that was what you were talking about with "logging VE Airflow as well as MAF Airflow" and I am. They both are close or even identical in most cases, all fields produce +/-1 to 3 or so, no huge numbers at all. What is really bizarre is the misfiring just sitting in park, so what I did was start there this weekend. I have tried reducing my spark advance for Idle and tried reducing and increasing "minimum air flow" table for idle area, all of them no luck. Is it possible that misfires don't get registered if the MAF has been disabled in the computer so I am really getting misfires in both configurations but just can't see them? I doubt it, but just a thought.

The misfires don't cause any DTC's but I know it can't be good and sense it doesn't do it in VE only it worries me. The car does produce alot more horsepower with the MAF on but does cause some low RPM surging that does trigger misfires but NOT all the time! I would like to use it but not at the cost of misfiring.

5_liter:
I did take a look at the MAF and is looks pristine, car only has 2000 miles on it with the CAI and 4500 total.

[ktoonsez]

Anyone else have any ideas? Do misfires usually occur due to lean or rich conditions?

[DSteck]

This is a great idea Doug. I run with the dyn airflow calcs disabled (MAF only) and it runs fine, I could use this method to derive my VE table.

Bingo. I'm on MAF only, and once my heads are back on and the car is retuned via the MAF, I'm going to derive my VE table with it.

To the OP, you may just have a trash timing table. If your MAF tune is way out, then your dynamic cylinder air is going to put you at an incorrect cell in the timing table. If I had to guess, though, I'd say your MAF is just totally out of calibration. Also, you may want to reduce the sensitivity of misfire counts because a cam will produce *some* false misfires because of inconsistent crank speed.

[5_Liter_Eater]

Do the '06 vettes have a VE table? I thought thats when they switched to the equation. Anyway, I tried this today and my VE was way off! Probably because I have artificial IFR numbers that keep me under 512 g/sec. I'm going to start another thread about it so as not to hijack.

http://www.hptuners.com/forum/showth...766#post138766

Sorry Toons I have not run into a problem with misfires. do you have another MAF you can swap out?

[ktoonsez]

Do the '06 vettes have a VE table? I thought thats when they switched to the equation. Anyway, I tried this today and my VE was way off! Probably because I have artificial IFR numbers that keep me under 512 g/sec. I'm going to start another thread about it so as not to hijack.

Sorry Toons I have not run into a problem with misfires. do you have another MAF you can swap out?

Wish I did just to see if it changes anything. When watching the MAF in the logs it looks pretty steady so I am pretty sure it is not broken, think I am pretty much screwed and will have to leave it off for life.

[LazMan]

06 Vettes are equations-based. I never have been able to get 'into' that conversion program. (Should be part of HPTuners ... idea!)

[Harlech]

Once you get a hang of the program it works like a dream. Once I get my Vette back I will try and see how a basically stock car handles running MAF only and see if the misfires come on. We were talking about it, and the only thing we could think is that the cam might be causing some issues down low leading to misfire or at least the car reporting misfire.

[ktoonsez]

Did some more tests again today.

Set "High RPM Disable" for Dynamic Airflow to 100 and "High RPM Re-enable" to 0.

This made "Air Calc Mode" go to "High" which causes all the misfires. So instead of obeying the STFT vs. MAF frequency reading, which were all negative, I took the value and made it a positive % and put into the MAF table ONLY for Idle area which produces a boat load of misfires. After doing this a few times the misfires actually dropped to almost nothing. But here is the kicker, the STFT were pegged at -26.6% and the wanted to stall because it was giving it so much extra gas. Again I watched the MAF hz in the log and it stays nice and steady between 2500-2700 at idle. So WTF is going on? There must be some other table for this damn LS3 that effects this MAF or something.

And of course after getting so frustrated, turned the MAF back off, set "Dynamic Airflow" values back to normal and all misfires disappear.