[Gregski]

MAF Scaling - Calibration

Arguably the Mass Air Flow sensor aka the MAF is the most important sensor on our Gen 3 engines (when it comes to fueling, the Temp Sensor is King overall, ha ha). We all have heard that the engine is nothing more than a sophisticated air pump. Buying into that analogy we begin to understand how the magic of mixing the the right amount of air and fuel at the right amount of (spark) time happens.

Fuel injected engines can rely on one of two air delivery methods, using the MAF sensor or using the MAP sensor (pronounced: Speed Density). To make things even more complicated, GM decided to use both, yes at the same time. Before we get to that, let's highlight the differences.

The MAF method ~MEASURES~ the actual amount of air going into the engine at that given moment in time. Now it seems perfect and makes you wonder why the MAF sometimes gets a bad rap, I mean who wouldn't want to know exactly precisely how much air is entering the system, right? Well the MAF has a few drawbacks, first, it don't know if the air is coming or going, so it measures air in either direction as it passes through it's super duper uber sensitive wire sensor that measures air mass based on how hot or cold that wire needs to be (blah blah blah). So if for some reason a wild cam pushes some back pressure air backwards in the intake manifold guess what? the MAF measures that as if it was going in. The second issue the MAF has is with TRANSIENT (pronounced quick) throttle changes, so you slam on the gas pedal, the MAF goes WTF, same goes for when you let off the throttle pedal right quick, the MAF can't exactly keep up. Thirdly, the MAF lives about a foot and a half away from the throttle body on a cold air intake housing or some sort of plastic tube, well that's where it measure the air, so what if there is a tiny hole or leak in that housing after the MAF, ie past it, the MAF don't know anything about it, so who or what accounts for that additional air, (pronounced: vacuum leak, ha ha)

Enter the MAP. If the MAF is the Accountant in the bunch, the Manifold Absolute Pressure sensor is the Mathematician if you will. Instead of measuring the air, the MAP ~CALCULATES~ it. Well technically the PCM does the heavy lifting but the MAP feeds some crucial information into that super duper complicated formula to come up with something called Cylinder Airmass. (Google: Ideal Gas Law, or don't ha ha). Cylinder Airmass as the name implies is the calculated amount of air that arrives at each individual cylinder, not the total eight cylinders at the same time. This use of the MAP is called Speed Density, you may have heard of guys running only in Speed Density mode, and that's a topic for an entire separate discussion, it just means they disabled their MAF and don't rely on it at all (not smart for daily drivers as it castrates what makes the LSx engines such good engines). The MAP / Speed Density which uses the Volumetric Efficiency aka VE table method also has its pros and cons, such as factoring in air temp, humidity, etc. all which effects the final computation, that's why GM decided to use both.

So majority of the time our Gen 3 engines are relying on the MAF, but when we transition too abruptly with the gas pedal either on or off the PCM takes a peak at the VE table ie Speed Density to keep the MAF honest. Also according to the factory settings, above 4,000 RPM we only rely on the MAF sensor and no longer use both methods (take that Speed Density only guys, joking) as the air rushing in is more stable at that point and the readings are more accurate.

Now we are gathered here today because we most likely done did an LS Swap, in which case we altered the intake track (ditched the fugly OE air box, changed the air filter, changed to a cold air intake, changed the location of the MAF, etc.) The precise calibration that the GM engineers/technicians have done at the factory has gone out the window. This is why we start by tuning\calibrating the MAF. It sounds intimidating at first, but don't be skierd.