Ecu calculation mysteries pt. 1

Discussion of tuning specific to MAZDASPEED3/MAZDASPEED Axela/Mazda 3 MPS vehicles
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EmPeEs6
Posts: 20
Joined: November 25th, 2013, 5:54 pm

Ecu calculation mysteries pt. 1

Post by EmPeEs6 »

I would like to publish one of the interesting findings I made while selftuning my Mazdaspeeds (MS6 + MS3 Gen 1) which concerns almost all internal target value calculations of the MS ecu such as load, wgdc etc.
Let me explain this using an arbitrary example:
If you dial in the following target load values (meaning that all relevant limiter/correction tables are already considered correctly):
...4k: 2.2 - 4.5k: 2.2 - 5k: 1.8...
In this case the ecu won't target 2.2 (or 2.1) for 4.5k rpm as you would expect, but significant less.
The reason for this observation is that the ecu does not only interpolate between 2 rpm "fixpoints" like 4k and 4.5k, but also takes the following value(s) into account for calculating the final target value, meaning that at about 4.3k the actual load will start to drop significantly since the target load value for 5k is much lower than the one for 4.5k!
This is also true for wgdc calculations - if you dial in this sequence: 4k: 30 - 4.5k: 30 - 5k: 50 then you will see the actual wgdc for rpm values slightly lower than 4.5k rising up to values which are higher than the ones actually permitted (which is: 30 + max upward correction value/e.g. the stock 20) - supposed that this is necessary in order to reach the corresponding target load.
Again, the ecu tries to smooth the shape of the target variable (wgdc/boost, load etc.) as much as possible by considering not just the directly adjacent calculation (rpm) points but also the following ones.
This is important to understand if you are self tuning and aiming for a certain target variable progression.
mituc
VersaTuner guru
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Joined: December 17th, 2011, 2:47 pm
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Re: Ecu calculation mysteries pt. 1

Post by mituc »

To avoid such issues always use the graph/visualize function for your load curve (and not only load) and make sure it is smooth. If it's choppy then the ECU logic will indeed apply some corrections/interpolations to it in its continuous struggle of anticipating what's going to happen at, say, 5k rpm based on what's happening at 4.5 or even sooner.
2008 Cosmic Blue Mazda 3MPS
Built engine + WMI + GTX3071 gen2, ~509BHP @34PSI
2008 Icy Blue Mazda CX7
Stock engine and exhaust (YES!!), JBR3" + GTX2867 gen2 + Autotech HPFP, self-tuned to 330-ish BHP
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