Boost Control User's Guide

Boost Control User's Guide

A guide on how to use the Elite Boost Control Function for typical street or mild racing use.


A wastegate, by its namesake, is a gate or valve, that lets waste gases of the engine bypass the turbocharger turbine.  If no wastegate is present, all of the exhaust generated by the engine would enter the turbine. This would drive the turbine with more energy which in turn would drive the compressor to generate more airflow and thus boost pressure. More boost pressure generates more exhaust pressure, which drives the turbine harder which drives the compressor harder, and around in circles, we go until swomething gives. The wastegate allows exhaust pressure to be regulated, so that only an amount of exhaust pressure required for the compressor to generate a certain amount of boost is allowed to reach the turbine.  This regulation is achieved by using a mechanical valve that can open to vent exhaust pressure between the motor and the turbine and instead send it to the exhaust system or open air for some applications. The opposite end of the valve is connected to a diaphragm. To keep the valve closed there is a spring that pre-loads the valve against its seat and altering the spring pressure will change the default boost pressure.

A break-away diagram showing typical external wastegate components.

Typical turbocharger configuration

A hose connection from the compressor housing provides boost pressure to the valve side of the diaphragm.  When the boost pressure exceeds the spring pressure the valve will open and begin venting pressure. This will regulate the turbine pressure and hence the boost pressure.


To allow boost to be adjusted higher than the spring pressure, an adjustment valve is placed in the hose that is supplying pressure to the wastegate diaphragm. With any aftermarket ECU a Boost Control Solenoid is required to do this function, and this solenoid is controlled with a duty (varying 0-100%) pulsed signal.   The purpose of the solenoid is to allow the pressure that is supplied to the diaphragm to be controlled by the ECU by venting some of this pressure.  By lowering the pressure supplied to the diaphragm more boost pressure is required to open the wastegate valve.  In general, as the duty is increased more pressure is vented from the diaphragm and this results in higher boost levels.  

To provide more control over the desired amount of boost pressure the duty signal can be mapped by the ECU.  There are two methods that we use to control the boost with an Elite ECU:  Open Loop and Closed Loop.


Open Loop Boost Control simply means that the ECU provides an amount of duty cycle from a table. The ECU itself does not vary the amount in any way, it simply pulses the solenoid at the duty that the tuner provides. Consider this as acting like an old-school T-piece but you can adjust the amount of bleed over table.


Closed Loop Boost Control means there is a Target Boost pressure that is trying to be reached, and the ECU can vary the amount of duty based on whether the actual boost pressure is above or below the Target.  This is the point where many believe magic happens and many users have difficulty in understanding how to set it up. In reality there is a logic behind the process that the ECU follows when it makes adjustments and understanding what all of the setting are in the system for is the key to getting the desired result.  As such the next section will cover what the settings all do with much of this explained in the Help section of ESP.

Configuration - Boost Control Tab

SettingOptionsDescriptionTypical Values

Open Loop

Closed Loop

Select whether to use Open Loop or Closed Loop for the control method. The difference is described above.Tuners discretion. For this guide we are focusing on Closed Loop operation.
Controlled Parameter

Manifold Pressure

Wastegate Pressure

Select whether to use Manifold Pressure or Wastegate Pressure. Manifold Pressure is used for most vehicles where the boost will be referenced from the same MAP sensor used for fuel and ignition control. Wastegate Pressure is used for CO2 two-solenoid control systems.Manifold Pressure for the sake of this guide
Output FrequencyEnter a ValueThe frequency that the solenoid is pulsed at in Hertz (Hz). The frequency used is dependent on the solenoid being used for boost control and is not really a value you tune. This value exists in the system so that we can correctly control the solenoid.For the HT-020400 solenoid. 33Hz works fine
Minimum Duty CycleEnter a ValueThe lowest output duty that can be output by the ECU. This overrides any table values that may be set lower. This value exists to prevent the ECU trying to make adjustments to the duty where the solenoid itself cannot physically have any effect on the boost pressure. Much like an injector, a boost control solenoid has a dead time and this duty approximates this.Typically around 5 to 10% for the Haltech solenoid. Set to a value where adding any extra duty causes boost to increase above the spring pressure.
Maximum Duty CycleEnter a ValueThe highest output duty that can be output by the ECU. This overrides any table values that may be set higher. This value exists for much the same reason as the Minimum Duty Cycle value. It prevents the ECU from trying to make adjustments where it is not possible to physically change the boost pressure.Can be left at 100% for the Haltech solenoid without adverse effects.
Control Point OffsetEnter a ValueUsed only with Closed Loop mode. This is the amount of boost that must be reached below the Target Boost before the ECU will start to do any closed loop control (hunting in of the target). For example, if the Target is 20psi and the Control Point Offset is set to 5psi, the boost must exceed 15psi before the ECU will try to make any adjustment to the duty to hunt in the target. This value exists to prevent the ECU from trying to make adjustments while the boost pressure is not stable. i.e. it is still building boost.Start with around 5psi. If there is initial overshooting use a higher value, if there is initial undershooting use a lower value.
Max DerivativeEnter a ValueThe rate of change of the boost pressure must be less than this before the ECU will try to hunt in the target. This value exists to prevent the ECU from trying to make any adjustments while the boost is unstable.Start with 15psi/sec. The MAP Derivative channel can be logged to see the actual values being used while boost is building and a little less than this value should be used.
Overboost OffsetEnter a ValueIf the boost pressure exceeds the Target Boost by this amount the output to the solenoid will be turned off. This is not related to a fuel or ignition cut and is meant to be a soft way to get boost under control. eg. If the Target is set to 20psi and this value is 3psi then the output will be disabled above 23psi.Typically start with 5psi above the Target while setting up the boost control, and dial down to around 3psi after tuning has completed. More at the tuners discretion than a hard rule.
Enable Spool AssistTick to EnableWhen enabled, the output duty will be set at 100% when the boost pressure is higher than barometric pressure. It will be on 100% until it exceeds the Control Point Offset, then the output will drop to the Base Duty. This setting exists to help build boost faster in some applications by venting as much pressure from the diaphragm as possible until we are near to the target. This can cause issues in some applications which is why it can be disabled.Use of this setting depends more on the application than a hard set rule. Suggestion is to disable this while learning how the boost control function works then experiment with using it after the tuning has completed. In some instances this setting can cause boost to overshoot if the plumbing to the wastegate is excessively long.
Closed Loop Min TPSEnter a ValueThe amount of throttle opening that must be exceeded before closed loop operation will commence. This setting exists to that the ECU does not try to make adjustments to the boost control output where the throttle is closed enough that it is not possible to reach the boost target. It prevents what is called Integral Wind-up where the controller is trying to add an excessive amount of duty on the output to try and reach the unobtainable target, then suddenly the driver pushes the throttle open more, which allows the more boost to be achieved, and with the larger duty being used the boost will now wildly overshoot the target.Start with 80% as this value ensures you have sufficient air flow to the engine to reach the full boost potential, and as such is in a controllable state.

Configuration - Long Term Trim Tab

Long Term Trim gives the Elite 1500 and 2500 models a way to learn the correct Base Duty over a period of use.  This can be helpful where it is not possible for the tuner to to spend time in all climates, altitudes or operating conditions present at the time of tuning.  Long Term simply looks at the Short Term correction and if it is a positive number it will learn a small positive amount.  The Short Term is a negative number it will learn a small negative amount.  Short Term refers to the amount of correction the closed loop system is currently applying to try and fix the amount of error from the Target at any given moment.

SettingOptionsDescriptionTypical Value
Enable Long Term TrimTick to EnableWhen enabled the boost control function will learn a correction to the Base Duty. Long Term TrimTuners discretion. Disable at first while learning how the systems works. When this is understood well then enable.
LTT Min TPSEnter a ValueThe amount of throttle opening that must be exceeded for the Long Term Trim to be active. This exists for much the same reason as the Closed Loop Min TPS, and that is to prevent the Long Term Trim from learning when it is not possible to reach the Target.Usually around full throttle, so 80 to 90%. It is possible to have Short Term working at less throttle but it is advised to not have it learn long term
LTT Min RPMEnter a ValueWhen the RPM is below this value the Long Term Trim is not active. This exists to prevent the long term from making corrections when it is not possible to reach the Target.Set this value to an RPM where it is possible to reach the Target. i.e. if your hardware only allows the target to be reached at 4200 rpm then 4200 is the value to enter here.
LTT Max RPMEnter a ValueWhen the RPM is below this above the Long Term Trim is not active. This exists to prevent the long term from making corrections when The engine may be reaching the RPM limiter.Set this value to around 500 rpm lower than your rpm limiter.
LTT Min GearEnter a ValueAvailable when the Gear Detection function is enabled, and you must be in this gear or higher for the Long Term Trim to be active. This exists to prevent the Long Term Trim from learning when the turbo is not capable of reaching the Target boost in a lower gear when the engines RPM rate is increasing rapidly.Usually 3rd Gear is needed for the system to be stable enough to learn good data. In most cases 1st gear and sometimes 2nd gear have the engine revving too fast for boost to be completely stable enough to learn values.
ResetSelectClicking this button simply resets the Long Term Trim table back to zero.N/A
Apply To Base TableSelectClicking this button will apply any Long Term Trim table values into the Base Duty table, and then it will reset the table to zero.N/A


TableDescriptionTypical Values
Closed Loop Base Duty CycleThe amount of duty the controller starts with for a given target boost pressure and should be the amount of duty to reach exactly that target value. The higher the target, the higher the duty you will need to enter because a higher duty is required to reach a higher target. It exists so that if you change the target boost pressure the controller can use an appropriate amount of duty to reach that target. Note that the default horizontal axis is Boost Control Target Pressure, not the actual boost pressure.Values in this table will greatly depend on the spring pressure. Start with values around the Minimum Output value for the Target pressure that matches your spring pressure. For higher targets you will add more duty. This is a table that needs to be adjusted by the tuner, or via the Long Term
Closed Loop Target PressureThe amount of boost pressure that you want to run. This table exists so that you can tell the ECU what it needs to target.Completely up to the tuner.
Controller Start DelayThe amount of time after the boost pressure has exceeded the Control Point Offset before closed loop (short term) will be active. This exists to prevent the ECU from immediately trying to adjust for error when we have not yet had time to reach the target. It gives the boost time to stabilise before adjustment is made. Adjusting too early would mean the ECU see that the boost is below target, which causes it to add duty. This extra duty would then cause the boost to overshoot the Target. So having enough delay time ensures that the boost has stopped rising and has reached the level it is going to get to for that given duty output.Starting with too high a value is better than starting with too low a value. Too low will cause overshoot. Too high will simply cause a short delay before the controller makes adjustment. Boost generally rises slower at low rpm, and faster at high rpm. So larger values are typically used at low rpm and smaller values are used at high rpm.
Closed Loop Proportional Gain

Using layman's terms, the Proportional Gain adjusts how reactive the system is relative to how much error there is. Increasing this makes the Short Term react faster.

Typically a low value is used to give the Short Term some reactivity to error. Going too high with Proportional can make the system oscillate at a high rate. Typically the boost control system is not very fast reacting due to the ECU output pulsing a solenoid, which vents pressure, which moves a diaphragm, which then allows the exhaust to change in pressure which then needs to drive the compressor to change the boost. This all doesn't happen instantly so making the system work too fast can have it chasing ghosts it cannot catch.
Closed Loop Integral Gain

Using layman's terms, the Integral Gain adjusts how large of a step the Proportional makes. Increasing this makes the short term use larger steps when trying to reach the target and help push the system to reach the target when the error is small.

Due to the above reasons, Integral Gain works better with controlling a system which is not so reactive. Start with  low values and if the target is not reached quick enough use higher values. Going too high can lead to slows speed oscillation.
Closed Loop Derivative Gain

Using layman's terms, the Derivative Gain controls the rate of change of the output. Increasing this can help prevent overshooting when the Proportional is set high but it can also prevent ever reaching the target.

Generally leave this at or near to zero for most applications. Going too high can lead to the Target never being reached. Derivative is more useful when we work with more reactive systems, like CO2 boost control.
Long Term Trim GainThe rate at which the Long Term Trim can learn. Because it is a Long Term it is meant to learn over a period of time. Instant trimming is called Short Term. It exists so we can find a point where data is learned accurately over time at a rate desired by the tuner.If the tuner has done their job and set the Base Duty table to good values, then the Long Term should not have much work to do. In practice, values around 100 to 200 are a good starting point.
Long Term TrimThe table where the Long Term Trim is stored. This is typically mapped using the same axis values as the Base Duty table.No settings here. Set to zero and start driving!


Multiple Target Setup

For this example I am using one of the Haltech Trim Modules to allow for more than one boost target setting.  This example shows the purpose of the Base Duty table.

For Setting 1 the target will be 10psi. For Setting 2 it will be 16psi.  For Setting 3 the Target will be 18psi but I want 20psi from 5000 rpm and higher.

My Target Boost level for this example

Because there is more than one target value the boost control solenoid needs to be pulsed at a different duty for different boost levels.   This is achieved by giving the ECU a starting point for the different boost levels.  The Closed Loop Base Duty table does this for us.  As can be seen in the below image, the duty is mapped over Boost Control Target Pressure so that as we change the Target the ECU knows which duty to use.

Base Duty table for this example

Based on this table, when I am using Setting 1 (Target is 10psi) the system will use 15% duty to reach this target boost amount.  If this is not correct I will be only adjusting the column only for 10psi until it does reach 10psi.  The other values in the other columns have no impact at all on the controller at this time.

When I am using Setting 2 (Target is 16psi) the system will use 38% duty to try to reach 16psi.  If this is not correct I will only adjust the 16psi column until I get 16psi.   The other values in the other columns have no impact at all on the controller at this time.

When I am using Setting 3 (Target varies between 18psi and 20psi) the system will use 46% duty until 5000 rpm to try to reach the 18psi target boost.  From 5000 rpm it will then use 54% duty to try and reach 20psi boost  In this case I would be tuning only the 18psi column under 5000 rpm and the 20psi column above 5000rpm.

It must be noted that it is very common as a Haltech Tech Support employee to see users who for some reason change the horizontal axis from Boost Control Target Pressure to simply Manifold Pressure. As can be seen by the above description of how the system works, doing this does not give the system a way to know a starting point to get to the Target.     It is also common to see users who set the entire table to be one value, which means the system will only reach a single target accurately and all other targets can never be reached correctly. 

Base Duty Set Too Low

This example has been created with our bench tester for training purposes, so real world experiences may vary slightly. The below image captures the typical manifold pressure that is experienced when the base duty is set too low.  It becomes more pronounced when the Spool Assist is Enabled and that is how this image has been created.

As the MAP (white) is building the controller is running at 100% duty (Spool Assist is Enabled) to help build boost.  Boost pressure exceeds the Control Point Offset which causes the Boost Control Output to drop to the Base Duty.  When it did this the MAP has dropped well below the Target Boost Pressure (red) because the Base Duty was set too low.  The closed loop controller now has to add more duty to fix this error before eventually meeting the Target.

The suggestion in this case is to increase the Base Duty until the dip in MAP is removed.  The Base Duty in other words should be the amount of duty that allows the MAP to match the Boost Target Pressure. 

Proportional Set Too High

This example has been created with our bench tester for training purposes, so real world experiences may vary slightly.  The image below shows the typical manifold pressure curve when Proportional is set too high.  

You will notice the Boost Control Output (Green) oscillating at a high rate due to this excessive Proportional.   As a result the MAP (white) is oscillating around the Boost Target Pressure (red) at a high rate.  

The suggestion is to drop the Proportional by a reasonable amount, maybe by half, and test again.

Integral Set Too High

This example has been created with our bench tester for training purposes, so real world experiences may vary slightly. This is a more difficult thing to try and capture the Boost Control Output acting abnormally, so unfortunately I can only show the change in MAP to show this effect.  

The slow rate oscillation of the MAP is a good indication that the Integral is set too high.  

As with the above example, the suggestion is to halve the Integral values and test again.

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