OK..long story short....C-6 2007 auto with Blackwing CAI...nitrous is a dry setup with two nozzles 3'' from MAF (ala Robert's set up)....MAF is descreened...everything works great EXCEPT P0171/0174 code keeps popping up.....data logged and LTFT was 25 at steady cruise...which explains the lean codes. So....I experimented and replaced MAF with a new screened MAF and LTFT is now around 10 and obviously no codes. I assume with the CAI and descreened MAF the LTFT went well over its limit....descreening seems to be the difference.

I did wide band 1000-5500 rpm and real time A/F's were fine if not a bit rich up top(11.8)so I don't think the engine is actually running lean and no knock sensors codes or datalogKR. Could I run the unscreened and just ignore the CEL and spray away? Or am I faced with either changing the MAF everytime I want to spray or changing the nozzle locations so I could spray screened?

Any help would be very appreciated.

 

Try posting in the tuning section. I descreened my MAF (C-5) no with no issues. From my understanding the screen is in to straighten the airflow as it goes through the MAF (to deal with the elbows some air ducts have). Cars like the C-5 and F-body with a fairly straight intake don't really need them (I know your a C-6, and the same should apply).

If you have tuning software like HPT or EFI Live, you can probably tune the MAF table to correctly reflect the change in airflow it is seeing with the screen gone, with that the code would not likely come up. Its a fairly easy process and is usually done after you modify the VE tables. Wideband is needed to do this though.

Hit the tuning guys in the forum up. See what they think.

Beer

 

Beer hit the nail on the head. Rescaling or a retune is sometimes in order with a CAI and/or descreen. You have just upped your volumetric Efficancy. Now with that said, many times, the computer will and can relearn enough to bring your balance back. Turn the code off, you may have to do this a couple times. However, with positive LTFT of 25, that means your adding 25% fuel for a percieved lean condition, so computer is doing what it should.

But here's where your running rich issue comes from, when ever you have positive fuel trims, then go wide open throttle, they are froze and added to your WOT Power Enrichment Multiplier and causing a false rich condition. If a LTFT is negative, then they are dropped at wot and no effect on commanded a/f (PE Multiplier) at WOT. Even with the screen in a 10% positive LTFT is not desired, getting them into a neg area through rpm band is the desired route to take. This should be done regardless of running a dry hit, or for that matter a wet hit. You just need a good base tune.

Don't run a dry hit with the screen in place. This can cause condensation to build up on screen and then you could have some other issues.

You won't be hurting anything spraying, as long as your not going lean on wide band, however, to get the most out of your n/a capabilities and the dry hit, a basic full tune should be done. Sounds like the system is working fine and how it should be, just a little fine tuning for best results is needed.

Hope this didn't confuse you? If so let me know and I will try to make it more clear, as sometimes I skip over things thinking some stuff is allready widely known?
Robert

 

Always good input from the Nitrous Doctor....