#2459 - 03/25/0804:43 PMUnderstand MAF and performance
Joined: Dec 2000 Posts: 5,240teamzr1 Owner - Pays the bills
teamzr1 Owner - Pays the bills Lives in Engine Bay
Joined: Dec 2000
It seems most people do not understand what the Mass AirFlow (MAF) purpose is and how many functions the PCM use the MAF outputs to adapt and adjust calibration
MAF output is seen by the PCM in lbs/min, frequency and grams/second that is also then converted to grms/cylinder.
Those values greatly dictate more then the airmass but also engine load, torque, line pressure and AFR needs.
Many cases people spend big money for aircleaners, porting MAF and some type of cold airbox.
When the MAF is mounted right off the aircleaner like a C5 Corvette the MAF is depending on the airpath NOT causing turbulance and rapid changing of the air temps.
It is even worse when the screen in the MAF is removed as it somehow would give performance gains ( BS told on car forums) as the having more of a negative effect to airflowing through MAF
In the testcases below simply changing how the air gets to the MAF not only highly effected the fuel trims going way too lean but also tricks PCM into thinking one side of the engine is leaner then the other side.
Notice that just a simple change of a crappy CAI design causes the PCM to THINK fuel trims are as much as 15% leaner then with a correct CAI design when in fact the grms/cyl report the same and so does the MAF in frequency and lbs/min
Even forcing injectors via a tune to go 10% richer made no difference as to reporting false lean conditions. Odd is how the air enters the MAF fools PCM into thinking one side of engine is leaner then other side as seen in the results.
With the MAF mounted to the aircleaner there is no distance or way for bad airpath to smooth and straighten air as it passes over the exposed sensors in the MAF's airstream.