MAF frequency table mods cause P0420?

[S2002S]

I have a completely stock 2007 z06. I added a Halltech intake and adjusted the MAF and PE tables a bit. LTFTs are negative (<10). I'm getting a P0420 code (Catalyst System Efficiency Below Threshold), that doesn't make sense for these changes. I restored the stock tune and intake and so far, no code.

Any ideas?

Thanks!

[BBA]

It causes a dead pedal on Trailblazer SS engines as well....

Then again, did you actually tune it against MAF vs STFT's?

Maybe you did, and this is why the MAF is not the best thing to tune. Injectors are better, take the error in MAF-vs STFT, figure out the differences and change the Injector parameters instead. Then recheck VE and MAF against STFT. You should minimize any changes to the MAF table, excessive changes are problematic.

But...that's just my thoughts on doing it in a way that won't exceed some weird PCM setting that throws shit out of whack.

[Blades]

BBA.. am I reading this correctly? Its better to scale the IFR tables rather than to correctly input MAF data? I'd say the opposite, unless the intake does not change anything after the MAF.. If it does.. then obviously the Hz->g/sec will change..

[BBA]

ANything you do that increases airflow needs a corresponding increase in fuel flow.

There are only a few ways to do it:
1. Complete VE and MAF tune.
2. Injector sizing.
3. Injector parameters.

The problem with changing the MAF calibration is your telling the PCM that more airflow is coming in at a given throttle that the PCM is calibrated to. Go far enough out and you get all kinds of weird problems.

All you need to do fuel injector changes is the percentage change in airflow from stock to modified, which you can get directly from logging fuel trims. Then run the calculations offsetting injector parameters against how much additional fuel you need (There is a guide available on this site, I think someone from HPT actually wrote it although it's geared toward replacing injectors with bigger injectors, same principle but easier calculations)

I've just seen too many people with dead pedal problems with LS2's and too many with setting DTC's from going too much on the MAF tables.

You can only lie to an engine PCM so far before it starts having problems with stuff going out of expected ranges.

Contrary to what most people think, the MAF is not the be all-end all of tuning for anything you do. It's only a small part of it.

[Kelp]

These are the two mainstays of tuning principle, air side, and fuel side, each having adamant followers. If one way is giving you trouble, try the other. Life is too short!

[EC_Tune]

If your injectors are stock, leave the IFR alone.... Anyone will tell you that. You will just end up getting really lost if you start changing those values when the injectors are stock. IFR tweaking was so 1998.... LOL

I've tuned tons of LS2/LS7's and tuning the MAF is *the* way to go. However, you will probably want to disable the LTFT's for tuning and tune specifically off the STFT's to get the best averages for the MAF tune. The LTFT's are simply an average of an average.

I have run into issues on the LS7 with a certain CAI kit (I won't name names so don't ask and it was very early on in the 06 model year) that really bungled the airflow across/around the MAF especially at low RPMs. Since it was only worth 2 HP anyways, the car owners just chucked the CAI to get their drivability back.