TECH advice. Everyone is telling you that your CAI can make your engine run lean. Im going to attempt to explain the reason why. First off, a mass air sensor is a critical component, and one of the most important in the entire engine management system. Its purpose is to accurately determine air flow into the engine. The PCM uses this critical data to determine programmed fuel metering and load parameters. If this critical component is providing erroneous data to the PCM, all engine management calculations will be impacted. So how does this device work? The sensor itself is a tiny heated wire. Air flow over the wire cools the wire and in doing so is correlated to a voltage signal from .5 v – 5.0 v. Each voltage signal is calibrated to a given quantity of air being inducted into the engine. The PCM deciphers the voltage signal to the amount of air flow used in the various engine management calculations. The voltage signal data recorded in the PCMs programming is called the transfer function. You may come across this term in your research, if youre doing any. Prior to the 3v engines, Ford used a mass air meter that had its own tube that was actually part of the meter. Regardless what air tube you put before or after it, it didnt have much effect on how the sensor reacted to air flow, since the tube it was installed in was fixed (i.e. never changed around the sensor). Now sharp bends before or after could potentially impact the direction of the air flow over the sensor wire, which could cause a different reading from the way the transfer function interpreted the signal, so it wasnt entirely fool proof. So here is whats going on with the 3v MAF sensors. With the newer engines, Ford decided to place the MAF sensor inside of a tube that is now part of the air intake system. If you take the sensor out of that tube and place it in a tube of a larger diameter, physics alone will tell you that there is no way it could interpret the air flow in the same manner. Air will flow over the sensor wire slower inside a larger diameter tube. If you want to conduct your own experiment use a regular garden hose. Put a smaller orifice nozzle on the end of the hose and open the valve. Now remove the nozzle and notice the difference in water flow. The same volume of water is coming out of the opening; it just comes out a whole lot faster with the smaller opening. In effect, the sensor is going to react to a smaller volume of air cooling the heated sensor wire when placed in a larger diameter tube. For example, lets say for a 1.08 v signal, Ford has the PCM calibrated to read that signal as 35 kg/hr of air. But now that the sensor is placed in a larger diameter tube, it may actually be taking 48 kg/hr of air to reach the same voltage. Assume for a minute that for a given throttle position the commanded fuel ratio is 13.2:1. Well if the transfer function is 37% off (48-35 = 8, 8/35 = .37), its going to command what it thinks is 13.2:1, but in effect will be 18.1:1 (13.2 x 1.37). That my friend is dangerously lean. My example may or may not be as extreme in reality, but its very unlikely that there will not be a difference throughout the entire rpm range. Adaptive controls can compensate for some minor differences in fuel trims over time, but it cannot compensate for differences as large as this example or even half of that variation. For the guy that claims to see no changes in short term and long term fuel trims, unless you have the ability to turn off adaptive control in your tune, you cannot make that assumption. Trust me; Ive had to build transfer functions from scratch back from data logging when Pro-M was the only game in town. As to warmer air ingested by the intake, it most definitely impacts the tune. The higher the perceived air temperature of ingested air, the more timing that is removed from the engine. There is a sensor that determines that air temperature and its an Intake Air Temperature (IAT) sensor. Any programmer that is capable of data logging will allow you to monitor IAT temperatures with whatever intake you desire. I have a hard time believing that an open element CAI is going to have the same temperature than one that draws air from outside the engine compartment. Perhaps that is not as true as the summer temperatures down here in the south, but if youve ever put your hand on any components far from the engine itself within the engine compartment after driving for a few hours, youll know what I mean. In any event, this is what all these guys are trying to tell you, but might not understand the logic behind what theyve learned. You can take this information with a big chip on your shoulder like all the others if you want, but these are the indisputable facts behind the advise youre being given. Your money, your choice.
Posted on: Tue, 23 Dec 2014 22:09:55 +0000
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