Monday, January 27, 2014

Tuning: AEM FIC MAF Clamp

Happy New Year everyone! Let's get back into the little problem with the MAF map! Earlier I found out that the original MAF map that I made up wasn't working because of the increased intake diameter. Here's the steps I took to correct it!

First things first. Why create a MAF clamp?

Basically, the Mass Air Flow (MAF) sensor has been designed for a specific diameter intake pipe for the stock engine's air intake capacity. By adding forced induction, due to the increased volume of air flowing pass the sensor, the readings can jump off the charts. When the factory computer reads the MAF reading and it's off the chart, a Check Engine Light (CEL) error will most likely pop. To overcome this, we need to set a ceiling value in the MAF table so any readings over this will be 'clamped' to the ceiling value.

The AEM team has done a great job and putting up as much information as possible to help out tuners with their products. The article that I used to create a new MAF clamp can be found here.

Before installing the turbo, I did log quite a bit of NA data. I used this data along with the awesome information from the Yaris World Forums (credit goes to all those who contribute to that thread!) to produce a basic MAF map. According to the sages in the forum, the 1NZFE MAF sensor has a linear working range from about 0.4 to 2.2V, but has the capacity to go up to 4.9V. The voltage clamp that I chose was 3.9V. This gives about a 1V buffer to the maximum of the sensor. My MAF map looked something like this

Remember, the AEM FIC software already creates a voltage maximum clamp in the settings section, but the values you put in the MAP, affects all other readings below the clamp.

You'll find that it resembles a lot like the fuel map which kinda makes sense. Both the fuel and MAF map affect how much fuel gets squirted into the motor.

From the map that I generated following AEM's instructional videos, there were two main issues: start-up and drive.


The little monster wouldn't start with the larger diameter intake because the MAF readings were too small. The smaller the reading, the less fuel the factory computer asks from the injectors. So to correct this I connected up the laptop to the FIC and had the car on. I looked at the current break point which would be on around the 14 PSIA (atmosphere) because the motor is off. When I cranked the engine, the currently highlighted break point moved down to the cell where the FIC was currently reading. I took note of those cells and slowly bumped up the MAF values. Through trial and error, I eventually was able to get the car to start and idle.


Next. As the intake piping is completely different, it affects all the values across the board of the MAF map. The simple way would be to measure and approximate the volume of the stock intake and compare it with the volume of the new piping. A even simpler approximation would be to compare the difference in diameter of the stock and new piping and determine how much larger it would be as a percentage. That percentage can then be applied across the board in your MAF map.

I knew that after applying the increase to the whole map, it would still require considerable tuning to make sure the MAF behaves appropriately, so I took an even simpler method. I first compared the increase in values that I had to apply in the start-up cells and applied a similar increase to the rest of the cells. I then went for a drive, remaining always in vacuum (i.e. don't allow the turbo to spool) and checked fuel trims.

I drove, adjusted and repeated until the fuel trims didn't fluctuate too considerably. This sorted out the vacuum section of the map. I then looked at the map and extrapolated the values into the boost portion of the map just by estimation. As boost increased, I slowly bumped up the MAF values to compensate for the increase in air-flow. With the adjusted values, I then went for a drive and in low boost (1, 2, 3 PSI), I checked the trims and made sure that the wideband read rich. Through this iterative tuning I was able to get a stable MAF map.

A little long winded but that's how tuning is!

Now this is how I got the MAF stablised. However, when I began tuning fuel... Things got complicated as fuel can be controlled not only by injector pulse on times, but indirectly through the factory computer by the MAF readings. Let's have a look at that next time!

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