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Practical Reflash Tuning: Load Measurement

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Load Measurement


00:00 - We've just discussed the two techniques used by the ECU to measure the mass air flow into the engine, and in this module we're going to see what this looks like inside the various maps of the ECU.
00:14 With the more common load measurement technique being the MAF sensor, this means the load axis is going to look a little different from what you might be used to, particularly if you've come from a background tuning MAP-based aftermarket ECUs.
00:29 There are various ways of defining the load axis, and you'll find that this will vary from one ECU to the next.
00:37 The most common technique is to directly define the load axis in units of mass air flow.
00:43 However, even when doing this, there are various units that are commonly used.
00:49 Common options here include grammes per cylinder, or grammes per revolution.
00:56 It's worth noting here that the MAF sensor will provide a reading in grammes per second, and the ECU will then calculate the current load based on the current mass air flow in grammes per second, and the current engine RPM.
01:11 For example, if we have a mass air flow reading in grammes per second, we could convert to grammes per revolution by accounting for the engine speed.
01:20 In this case, the calculation the ECU does is shown here.
01:25 Mass airflow in grammes per revolution is equal to the mass airflow in grammes per second multiplied by 60, and then divided by the engine RPM.
01:37 We're multiplying the mass air flow by 60 to change the units from seconds into minutes, since we're measuring engine speed in RPM, or revolutions per minute.
01:49 This means that if we had an air flow rating of 150 grammes per second, at 3000 RPM this would equate to 3.0 grammes per revolution, whereas at 5000 RPM it would equal 1.8 grammes per revolution.
02:07 To calculate engine load in grammes per cylinder then, we would use the equation shown.
02:13 We start out the same, multiplying the mass air flow by 60 so we can work in units of minutes.
02:20 We then need to divide this by half the engine RPM, since we only have one intake stroke for two engine revolutions.
02:29 Lastly, we divide the result by the number of cylinders.
02:34 We don't necessarily need to make these sorts of calculations when we're on the dyno tuning, however I find a lot of tuners moving from stand-alone ECU tuning to reflashing never properly understand what these load units mean.
02:50 The last load measurement I want to discuss is the technique employed by Mitsubishi ECUs, where load is represented as a percentage.
02:59 For example, 0 to 300%.
03:03 It's a common mistake to believe that the load percentage is a representation of manifold pressure in kilopascals.
03:11 That's to say that a load value of 100% would equate to 100 kPa, or atmospheric pressure.