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Discussion Starter · #1 ·
I've been doing a lot of research about the MAF sensor and intake calibration, but still have the following question:

If I were to install an APS 70mm CAI on a stock car, I understand that initially the car would run very lean due to the increased pipe diameter, but after some time wouldn't the ECU eventually learn itself back to the targeted AFR's by adjusting the fuel correction factors? The intake calibration map would still be off, but the learned fuel corrections would eventually compensate, wouldn't they?

Please help me understand this.:confused:
 

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06stiman said:
I've been doing a lot of research about the MAF sensor and intake calibration, but still have the following question:

If I were to install an APS 70mm CAI on a stock car, I understand that initially the car would run very lean due to the increased pipe diameter, but after some time wouldn't the ECU eventually learn itself back to the targeted AFR's by adjusting the fuel correction factors? The intake calibration map would still be off, but the learned fuel corrections would eventually compensate, wouldn't they?

Please help me understand this.:confused:
Here is my understanding:

Most stock narrow band oxygen sensors are capable of reading 14.7/1 but not much more(or less). For example, they will only read from around 14.3/1 to 15.3/1. The sensor can not understand an actual AFR under or over this range.

During easy cruising (closed loop) the ECU uses the stock Oxygen sensor (narrow band) to adjust the AFR to a target of 14.7/1. The reason is like this. At 14.7/1 (this means 14.7 pounds of air to 1 pound of fuel) the amount of air will combine with all of the available fuel. This is the best condition for the catalytic converter to do its job thus providing for a better environment.

So, what happens when we mash it to the floor?

Well .. it is not so easy to explain in detail but at a very high level, this is what happens: The ECU disregards the oxygen sensor readings (open loop) and uses a fuel map to determine how to work the fuel injectors. The fuel map is just a table of numbers that an engineer (or those of us tuning on our own) has established to define the proper injector pulsing for a set of parameters. The parameters considered include: Intake air temp, Intake air flow, RPM, Throttle position and many more. The stock ECU adjusts the injector pulsing according to the data in the maps. A simple example may be expressed like this:​

The fuel map tells the ECU to pulse the injectors 10 times when ever the RPM is 1000, the air temp is 70, the throttle position is 25% open and the mass air sensor voltage is 1.25v.

So.. to answer your question... the larger intake pipe diameter would cause the same amount of air going through the intake to slow down (pipe size). The MAF sensor would detect this and report a lower voltage to the ECU Less voltage from the MAF would cause the ECU to pulse the injectors less. The ECU can make corrections in "closed loop" but when you mash it the maps take over so it can't compensate.

Here is a scary example of what actually happened to me at the track last week.

-- I had just installed my new Typhoon intake, I failed to tighten up the clamps and during one of my 1/4 mile passes, the intake tube slipped out of position. This provided a small crack that the turbo sucked air into completely bypassing the MAF sensor. So... the result was my engine was sucking more air than the sensor was detecting so my ECU slowed down the pulsing of my injectors causing my AFR to go from 11.1 to 1 to 12.5 to 1

Luckily for me... the knock sensor started to hear noise and the ECU pulled mega timing and saved the engine...

Sorry for the long post, I hope it helps you understand the basics...

Jeff B
 

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Discussion Starter · #4 ·
Thanks TQ, your response helped out a lot!:tup:
 

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Not exactly a technie response your looking for... but the APS 70 MM cannot be run without being tuned... you will simply hurt the car. The stock ECU does adapt to some variation, but apparently this is a large change to the intake tract and would be too much to compensate.
 

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Discussion Starter · #6 ·
TurboQueef said:
The ECU can make corrections in "closed loop" but when you mash it the maps take over so it can't compensate.
I thought when you "mash it" the ECU goes into open loop where it only applies the latest learned long term fuel trims with no short term fuel trims. After a long enough period of time, wouldn't the learned long term fuel trims mapped to the WOT position be applied in such a way that the resulting AFR is close to target?
 

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So.. to answer your question... the larger intake pipe diameter would cause the same amount of air going through the intake to slow down (pipe size). The MAF sensor would detect this and report a lower voltage to the ECU Less voltage from the MAF would cause the ECU to pulse the injectors less. The ECU can make corrections in "closed loop" but when you mash it the maps take over so it can't compensate.
Resurrecting this oldie, didn't want to start a new Thread.
So, according to the Queef's explanation above, which makes a lot of sense, I guess the MAF is "flawed" in a sense that it cannot directly determine the amount (volume) of air coming through, but it merely detects the speed of the air, which combined with the constant, predetermined diameter of the intake pipe, gives it the volume of the incoming air. Correct?
So theoretically, if you had a MAF able to measure the volume of incoming air (directly), you could put any diameter intake on, without the need to re-tune, correct?
 

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Yes, but such ting does not exist in the automotive world. The way a MAf works is that it heats up some thin wires that are in the sensor. This in part uses up voltage to heat them up to a constant temperature. When more air is flowing threw a given diameter the maf is going to need more voltage to keep the temperature constant. The ecu takes this voltage and translates it into amount of air passing threw a given diameter "Volume" at a given temperature. With out programing "scaling" the maf the ecu would use the same ecuation values for the wrong sized housing.
 
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