Originally Posted By: electrolover
Actually a lot of people notice short term mpg increases until the cpu sets new parameters. Trucks like mine are the worst about it. People put cold air intakes on with out programs and it leans em out pretty bad. The cpu cant compensate enough. The increase in mpg in this case is not good. It means your running lean and thats dangerous.
Reducing restriction will give you more air across the board. It doesn't matter where your throttle is.
Computers are funny anyway. I cleaned my throttle body and it idled high for two days after that. Its like they are constantly resetting, but really slow at it. At idle .050 of carbon is a big restriction in the tb, I guess.
The leaning out happens because the MAF readings are skewed, not because of the "mad increase in air".
The ECM has a table that gives it base references for how much air means how much fuel. A CAI has no effect on these values, if the engine needs to ingest more air, it will ingest more air. The MAF registers the increase in air, and the ECM adds fuel accordingly.
The biggest restriction in the air intake tract is the throttle. It certainly matters where the throttle is. If the throttle is passing 50CFM at idle and your factory airbox can move 1500CFM and you replace the factory filter with a K&N element that can move 1700CFM (clean), do you honestly think the engine is going to magically ingest more than the 50CFM it requires to idle?
Computers aren't "funny". Computers respond according to the inputs they expect and react with the values they have in their base tables as well as their adaptives. However, GIGO. Garbage In, Garbage Out. If you install a CAI that changes the perceived airflow across the MAF, you end up with skewed readings, and the ECM has to try to adapt (through its adaptive strategy) to these changes. This takes time. And sometimes, if the skew is beyond the ECM's compensation ability, it may set a code or require a chip/tune to correct for this alteration. It doesn't mean you added "way too much air for the ECM to handle" (MAD CAI POWAZ, YO!). An engine will only ingest the amount of air it needs and the factory electronics are MORE than adequate for the stock power levels as well as decent percentage above that. Ford used 19lb injectors on engines with a wide range of power outputs. The 205HP 5.0L Explorer and the 260HP 5.4L Expedition had the same injectors. Ford also used the same MAF's in applications with large power rifts (like on the 4.6L and 5.4L). And a CAI certainly doesn't change the power output by such a significant margin that the stock components are incapable of handling it.
With regards to your point about your TB, yes, unless you cleared the adaptives in the ECM, it expects a given amount of airflow for a throttle position at a specific amount of load. In cleaning out the carbon, you changed one of those values and it had to adapt to those changes. It doesn't mean it was starving for air before.
At WOT, 100% load, max RPM, is when an engine will ingest the most air it possibly can. The factory air filter is sized in accordance to that, with a healthy safety margin to account for dirt loading and restriction. The air filter flows way, WAY more air than the airbox, particularly if there is a silencer in place. The air intake tract on the other hand is a compromise due to noise control, flow characteristics that affect the power curve....etc. They are often fitted with a silencer or silencers as part of this. Usually, the system itself is capable of flowing significantly more air with the silencers removed, but keep in mind that the factory power rating for the engine on any of the systems designed in the last decade or so are a product of the engine operating with the factory air intake tract in place, right down to the silencers. Also keep in mind that the factory exhaust systems are designed in the same manner. What goes in, must also go out.....
It is quite common to get the same "gains" as an aftermarket CAI by simply pulling the silencers out of your stock intake system. This also means you won't skew the MAF curve and mess up your adaptives. The only place where this makes a difference of course is under extremely high load @ WOT where the extra available airflow can potentially be utilized. I say potentially because if your engine is capable of ingesting 700CFM at WOT, 6,200RPM @ 100% load, and your factory intake tract can move 900CFM, removing the silencers does absolutely nothing. On the other hand, given those same parameters and your silencers restrict flow to 650CFM, you will pick up a few peak HP. But certainly not enough to overwhelm the factory electronics.
What often happens is that you take the same above characteristics, but you ditch the stock air intake tract, which the stock MAF is designed to work with, and you fit a CAI to it that alters the airflow across the MAF, skewing the readings and making things lean or rich. Sometimes the ECM can adapt for this if given enough time, other times it can't. These are often the situations where people think that the factory system sucked so bad that when they stuck on their mad blingin' CAI that they increased the airflow so much that the ECM couldn't handle it. This is not the case. What they've done is altered the parameters the ECM expects enough to skew it beyond the adaptive capability of the electronics. These are not the same thing. In most MAF-equipped vehicles, load is a derived value based on throttle position and perceived air consumption by the MAF. You change what the MAF sees relative to airflow, you screw up this relationship. IE, more air passing across the element relative to its position in the airstream means more perceived load, more perceived load means it will add more fuel for a given throttle position. This doesn't mean it ACTUALLY has more load, it just THINKS it does. The O2's will tell it that it is wrong, and it will use feedback to correct for it as long as it is within the range of compensation. Then of course you have the opposite, which can happen when the MAF is closer to the inside curve of the CAI tubing. Airflow is slowed across the MAF element, which it perceives as lower airflow, ergo, less load. This results in a lean condition.
The above is why the factory air intake tract is designed to put the MAF in a specific position. If it is in the plumbing, the plumbing is usually "keyed" so that the MAF can only go in the right spot.
I've played a lot with this stuff, "clocking" the MAF was a common technique to deal with rich/lean idle surge issues on CAI-equipped Mustangs. Altering the position of the MAF in the airstream changed the data observed by the ECM, which then effected the strategy and if you were outside the range of the adaptives, could put it back within the range, and eliminate the surge.
With the right datalogging gear on a modern vehicle, you can observe all of this. MAF voltage, load, feedback, adaptives.....etc.