Friday, March 21, 2014

Tuning: Re-tuning with a Temporary MAP Sensor - Part 1


Alright! Now that the wiring is complete and the signal from the Boost sender was successfully identified, now comes tuning.

Since the on-board MAP is gonners and now the main load will is MAF (boost sender), let's do exactly that, let's change all loads in all maps to MAF (boost sender). Don't let this confuse you, the factory MAF is not the load, remember, we've loaded the MAF IN wire with the boost sender signal, so the MAF load is actually MAP... In a way.

Nice. We'll need to transfer all the values from the MAF map to the Analogue A map, this will now be used to tune the factory MAF sensor. Unfortunately, we can't simply set a voltage clamp in the Settings menu, a max voltage will need to be set manually in the map itself. The MAF map will now be zero'd out ensuring that the offset mode is set to percent.

Now let's work out the Y-axis (the new load range) that we need to apply to all maps as the current Y-axis is mapped to MAP values.

Unfortunately there's no datasheet or info on the voltage vs pressure range of the boost sender. But we can do some black box analysis. We know from previous testing that at atmospheric pressure (0 psi or 14.7 psia) the voltage output from the boost sender is 1.1V. Great! That means, when the voltage exceeds 1.1V the motor will be going into boost territory... But how much?

Let's make some estimations.
  1. From existing fuel MAP, I found the break point at 0 psi or the transition between vacuum to boost and set that point to 1.1V.
  2. I then set the lowest value to 0V or 0.1V, then grabbing all values from 1.1V to 0.1V, I "Calculated" between those values by right-clicking the selection and clicking "Calculate" from the context menu. This fills the in-between cells with incrementing values between 0.1V through to 1.1V.

So now I've got breakpoints for the vacuum section. Next I want to know what voltage corresponds to the different breakpoints of the actual boost gauge so I can work out the boost range of the Y-axis (i.e. 1.1V and onwards).

There are four breakpoints between 0 psi and full vacuum as read on the AutoGauge Boost Gauge. Which means 1.1V / 4 = 0.275V for each breakpoint. Let's check! It's time to start the motor.

After starting the motor, I was idling at the first breakpoint of 20 kPa (vacuum) with a MAF voltage of 0.31V as read from the AEM software. Which is about right. So taking this value, I know the max boost of the turbo is about 7.5 psi which corresponds to:

0psi = 1.1V
5psi = 1.1V + 0.31V
7.5psi = 1.1V + 0.31V + 0.155V (half way between 5 psi and 10 psi) = 1.565V

Nice. I then put the 1.56V as the third cell from the top in the Y-axis and "Calculated" down to 1.1V giving me the full boost range.


The additional three rows above 1.56V I'll use as buffer in case there's over-boost by setting the max voltage as 2V and calculate down to 1.56V.


With the new Y-axis scale, I copied this to all maps and re-aligned existing values to the approximate breakpoints of the new scale.

It's time for a test drive!

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