The ME ECUs features several advanced boost control strategies. These strategies allow better control of the engine's boost when using a turbo-charger by modulating the pressure seen at the actuator, therefore changing the position of the waste-gate - the more open the waste-gate, the less exhaust gas passes ‘through’ the turbo turbines, and hence less boost is created.


You can also use electronic boost control to allow ‘boost switching’ - i.e to have a high/low boost switch on the dash. Note that even though you are changing the maximum boost, you can usually just use one VE/Ignition table to cover all settings - i.e in low boost the engine may only use up to the 160 kPa load line, then in high boost, it may reach the 250 kPa area of the map - no need to have separate maps, just map both high and low boost areas on the same VE table. (Note that the ME221 does have switch-able VE/IGN/Boost maps however if needed for advanced applications, though as shown above, they are not really needed for 99% of applications.)


To use this feature you will need a 3-port boost control solenoid, and a spare Low-Side driver channel on the ECU. The drive frequency and duty ranges are usually specified by the manufacturer, or though much like the idle settings, the optimal values can be found by using the manual duty mode and experimenting. Most off the shelf units, including the one we supply (Part# ACC_BCS_1) work best at 30-60Hz.


There are several control methods available to use:

●        Manual Duty Mode

●        Closed Loop

●        Open Loop

●        Boost-by-Gear


The ECU also allows over-boost protection, as well as ‘boost scramble’, whereby an over-boost pressure is allowed for a short time, such as what occurs with larger turbo during initial spool.


HINT:
Boost is usually referred to as ‘Gauge’ pressure, meaning it doesn't take into account the typical 1 Bar (100 kPa) of atmospheric pressure that already exists all around us (at sea level). To say we run 1 Bar of boost, means the inlet manifold pressure with reference to a vacuum (or ‘Absolute’ pressure)  is actually 2 Bar, or, in KPa, 200 kPa. Hence you can see that a MAP reading on the ECU of 150 kPa would mean we have 50 kPa of boost, or 0.5Bar of boost. (There are 15 psi to every 1 Bar - so 50 kPa = 0.5 Bar = 7psi.)


Below is a picture of the Boost Control driver, as seen in FW 1.8.4:

Boost control can be as simple or as complex as the user requires. As we detailed above, as long as the VE/Ignition tables are mapped for the full boost range, then we can increase/decrease boost as required up to the maximum ‘mapped’ level, as well as change how the turbo spools.


We assume you have installed the hardware correctly, such that as we increase the duty to the waste-gate/boost control valve, we in effect decrease the amount of pressure placed against the waste-gate, and therefore allow the turbo use more of the available exhaust pressure to increase manifold pressure.


If the opposite is true, you can select ‘Inverted’ in the ‘PWM Solenoid Control’ option box.


The most basic of boost control - and indeed the first step to setting it up - is to operate the valve in ‘Manual Duty’ mode, as seen in the image above.


Now, be sure to set the valve's drive frequency, which is usually specified by the manufacturer of the valve - numbers from 10-60Hz are typical.


With this set, you can change the ‘PWM Manual Duty’ field from 0-100%, to find the min/max duties (where no change above or below these points changes the boost level) and also to find some various duties for different boosts when running in ‘Open Loop’ mode.


So, for the sake of example, let’s say we find that duties of 33% and below show actuator pressure - that is - the boost pressure when the system runs fully mechanically (and in this example we have the actuator boost pressure set to 7 psi, or 150 kPa Absolute) - note that if the valve were to fail, this would be the boost that would be ran. We would note this down as our ‘PWM Min Duty’. Likewise, we may find that duties of 60% gives us (our desired in this example) around 1 Bar of boost, or 200 kPa Absolute.


Now it may be thought that 60% would be the number to put in our ‘PWM Max Duty’, however - this is not actually correct - the boost may reach the target at this duty, but the turbo may spool faster if we allow it run to 100% duty (and therefore keeping the waste-gate completely closed) when at low RPM. Again, the manufacturer usually gives the Min/Max recommended duties for valve). It's not easy to discover this ‘Max’ number on your engine without risk of over-boosting, and engine damage, but it can be found using the open duty table, which we will cover shortly.