Originally Posted by synolimit
this kinda contradicts its self. your saying the MAF can make the corrections and thats it! but then you say the tuner needs to adjust scaling. so ill hold what i said first. the MAF can adjust BUT not much! thats why you cant throw in 1000cc injectors and be ok. why you cant add a CAI, DP, header, UP CBE and be ok. i put on a CAI with no adjustment and shot up to 33MPG. the car was WAY to lean. the AFR and scaling still needs adjusted because the MAF CANT do it all.
You're missing the point. Putting in larger injectors changes the fuel flow characteristics of the system, not the airflow. Putting in a CAI changes the MAF scaling, thereby throwing off the MAF sensor. If the intake and fuel systems are kept consistent, and no leaks are presented, the resulting a/f SHOULD be very close barring issues with the tune.
The flip side of this, however, is VE. The MAF is not the end all, be all of fueling in the ECU. The ECU receives the MAF signal, uses the calibration table to convert it to an airflow value, and then uses this airflow value along with injector calibration values, trim tables, and VE calibration data to calculate the required injector on-time to achieve the desired a/f target. So if we are indeed keeping the fuel system and intake system consistent and leak free, and the tune is set up properly to handle the given range of airflows, a change in VE could still result in a shift in a/f. This is because VE defines how efficiently the engine uses the air that it consumes. If you increase VE and keep all other parameters consistent (including airflow), you will inherently see a shift in the a/f.
The problem is that its very difficult to say which inconsistency caused the a/f swing without doing an extensive pressurized leak test of the exhaust and intake systems. Now, if indeed a VE change is the actual cause of the a/f swing, its even more necessary to fully tune both setups individually to present actual gains from the part since a change in VE can call for very different ignition advance, cam advance, and a/f profiles.