Mapping Outputs

This page describes how to configure powertrain actuators using SXTune.

Idle Control - Cable Throttle - No IAC

Procedure for Setting Idle

This guide is for customers using closed loop idle control, with a cable operated throttle body, without an idle air control valve (IAC). Since air cannot be adjusted by the ECU with this configuration, spark advance is used to raise or reduce idle speed as necessary. As with any closed loop control system, the base setup should be set reasonably close (a little above) to the desired idle speed. In cases where the vehicle has multiple throttle bodies, extra steps are required in order to reach an even idle. The idle setup for these types of applications is an iterative process where each adjustment can affect previous adjustments. The car should first be warmed to its normal operating temperature before the setup procedure is begun. The TPS should be calibrated according to the procedure detailed in the Configuring Input Sensors section of this manual (see TPS(Cable Throttle) for details). The procedure detailed below should be followed in order to complete setup.

1. Multiple Throttle Bodies: If your application has multiple throttle bodies then a synchometer must be used to balance the air volume intake between the throttle bodies. The larger air volume is turned down using the air bleed screw on the throttle body so that it matches the other throttle body or throttle bodies.

2. Turn Off Closed Loop Idle Control: In the Idle Speed Control group, turn off closed loop control by setting the Idle Control TPS/PPS enable limit (%) to 0.0

3. Lower RPM on Throttle Stops: The idle value should now be adjusted manually to be around 50 RPM more than the desired idle RPM when closed loop control is used. This should be done by adjusting the throttle stops.

4. Set Lambda: The fuelling can now be adjusted for lambda 1. If a wideband lambda sensor is not fitted then an exhaust gas analyser should be used. It is also possible to estimate lambda 1 by making the fueling very rich and then taking fuel out gradually until the RPM just drops. At this point a small amount of fuel can be added again to raise the RPM. This gives an estimated lambda 1 but it is not a recommended method and a gas analyser should be used.

5. Recalibrate TPS input: The TPS input calibration should now be reset as above since the lowering of RPM on the throttle stops will have affected the configuration.

6. Recheck Adjustments: The fuelling can now be checked again for lambda 1 and adjusted as necessary making sure that the RPM remains around 50 more than required. The throttle bodies should again be checked for air balance and readjusted on their air bleed screw as necessary. The RPM can again be adjusted on the throttle stops if necessary. The TPS input configuration will then need to be adjusted again in the case that the throttle stops have been adjusted.

6. Set Target Idle Speed: The target idle speed should now be set in the Target Idle Speed (rpm) map. A typical map is shown below. The idle speeds shown for temperatures below normal operating temperature will not be achieved (since spark advance is the only method the ECU has to adjust the idle speed). The can be set to the open loop idle speed when warm. Temperatures encountered under normal conditions should be set to the desired idle speed. Commonly this can be around 1000 RPM for example for a mini.

7. Closed loop idle control can now be turned on by setting the Idle Control TPS/PPS enable limit (%) to 0.8. Closed loop control will now alter spark advance as necessary to achieve the idle speed set in the map (for normal operating temperatures)

Configuring Turbo Boost

Elements Involved in Boost Control

Using SXtune software, boost is configured through 4 related maps which are found in the “Boost Control” group. These maps are:

  1. Base Duty Cycle
  2. Target Manifold Press
  3. Integral Gain
  4. Proportional Gain

The Base Duty Cycle is the main map which you will need to configure in order to control boost as a function of RPM and load (load is established via TPS as manifold pressure cannot be used since it is the variable we are attempting to control). Most importantly, correct configuration of this map allows you to limit maximum boost to a level which avoids damage to your engine. You should not rely entirely on closed loop control (CLC) to limit maximum boost. Any CLC cannot instantly correct an output and therefore an engine may be subject to excessive boost monetarily, before the CLC correction has taken effect, unless the Base Duty Cycle map is correctly configured. It is therefore advisable to disable CLC temporarily whilst configuring the base duty cycle to provide a safe level of boost for all load and rpm values, before enabling CLC again to act as a safety net

The Target Manifold Press map sets the desired boost as a function of RPM and TPS.

The maps for Integral Gain and Proportional Gain set the closed loop boost control. In basic terms, they use a combination of proportional and integral feedback in order maintain the boost to that set in the Target Manifold Press map. The values in these maps will determine how quickly the boost will arrive back to the target boost and by how much the boost will overshoot and undershoot the desired value as it attempts to arrive exactly at the target pressure set in the Target Manifold Press map. In most applications, it will not be necessary to alter these values. If your application is suffering from excessive oscillation in boost pressure, or the boost isn’t arriving to the target pressure quickly enough, then consult with SCS for advice on a new configuration for your integral and proportional gain maps.

Configuring the Base Duty Cycle map

Working in in the Boost Control group, the following procedure should be followed in order to configure the base duty signal:

1. Disable the closed loop control by setting the RPM (RPM thresh enable boost CLC) at which it begins to operate to a very large value which cannot be reached (e.g. 20,000). This is done in the Boost Control Variables page.

2. Open the Base Duty Cycle page and save the existing map using the save icon on the toolbar. This can then be restored later if required.

3. Highlight all cells in the map and set them to 0. Click save (currently red) at the bottom of the window to copy this change to the ECU (changes to green). With no boost being applied, this is now a good point to configure the fuelling and spark advance maps in the Base Mapping group (see relevant SCS-Delta manuals for help with configuring these maps).

4. Live data is shown in the fields on the right of the page. If you don’t already know it, the value of the wastegate actuator spring (in terms of manifold pressure) can be now determined by increasing RPM and observing the maximum MAP value. This value can be set as the minimum target boost if necessary, but should already be correct (normally 1500 mBar e.g. 500 mBar boost pressure before the actuator spring opens the wastegate).

5. On the Base Duty Cycle page, the values in the map can be increased to begin bleeding air away from the wastegate actuator, thus delaying the point at which it opens and so increasing boost. Initially, a value of 10 can be added to all cells and boost can be checked for different load demand throughout the rev range. A common approach is to check the boost for maximum load first in order to get an idea of the extremes and then adjust the rest of the map, slowly increasing the duty cycle until the boost pressure matches that in the map shown in the Target Manifold Press page. The difference between the actual MAP and the target can be observed in the Live Data field: MAP Error mBar field.

6. When a suitable open loop boost has been obtained, the closed loop control can be reenabled by returning the RPM thresh enable boost CLC to its previous value. The fuel cut MAP threshold should also be set to a safe value for your application.

Mapping Target Lambda

Setting Variables

Make sure the sensor has been calibrated (see Lambda Sensor Calibration for details). Before populating a target lambda map, it is necessary to configure the variables which will determine how the map is used

1. In the Fuel Closed Loop Control group, select Fuel Closed Loop Control Variables and set closed Loop Control Mode to Wide Band Control.

2. The Maximum Closed Loop Correction value will set the maximum by which correction can alter the injection pulse width set in the Main Fuel Map (found in the Base Mapping group menu). For example, consider a global maximum pulse width variable set to 10ms and the value in the base fuel map for 2000RPM and load of 400mBar is 50. Before closed loop correction, the final pulse width would be 5ms. With a maximum correction factor set to 30% the maximum amount of fuel pulse width the closed loop correction could add or remove would be 1.5ms. It is recommended as a starting point to set Maximum Closed Loop Correction to 30%

3. Closed loop lambda control can be limited to operate up to a defined RPM and Load using the RPM Limit and Map Limit fields (Note: the load will show as TPS Limit (rather than Map limit) if your load input type variable has been set as Throttle Position in ECU Configuration field under the ECU Configuration group). For example: setting these as 4000RPM and 400mBar means that closed loop control will be turned off above either of these limits and the fuelling will be determined by the Main Fuel map and other correction factor.

4. The gain terms determine how quickly a difference in actual and target lambda is corrected and by how much the correction can overshoot the desired value. Suggested values are 100 for the Wideband Proportional Term, 80 for Integral, 20 for Derivative and 500 for the Integral Saturation Term.

Mapping Target Lambda

The target lambda values for various RPM and load conditions are set in the Wideband Target Lambda map. A typical Wideband Target Lambda map is shown below. Many tuners prefer to have lambda 1 at low loads and speeds. In contrast, when the engine is operating around the rpm where it makes most power then many prefer to run the engine at around .85 to .88 lambda in order protect the engine from excessive heat. When running turbo charged engines, many tuners tend to choose 0.8 lambda when at the RPM where the engine makes its maximum power. This value avoids excessive heating as well as making the engine less prone to knock. In all cases these are general rules of thumb preferred by different tuners and customers should carefully consider their own application’s requirements.

Editing Breakpoints

To set up the graph axis more breakpoints (rows or columns) can be added (up to a maximum of 8) using the edit icons. The windows provide for a maximum of 8 breakpoints on each axis. If less than 8 breakpoints are required on either axis, then the lowest breakpoint values can be repeated as shown in the MAP breakpoints edit window shown below. Notice that there are 5 unique values (breakpoints 1 to 4 have the same value) on the x axis (load) giving the 5 rows on the Wideband Target Lambda map. Return to the map view by pressing the pencil icon.

Improving Open Loop Lambda

As in other cases where closed loop control is used (e.g. turbo boost control), the accuracy of the base map (Main Fuel Map) should be as close as possible to the desired lambda values for all RPM/Load combinations. For this reason, it is recommended to log lambda correction in real time and note the RPM/Load values where a lot of correction to the base fuel map is required in order achieve the values in the Wideband Target Lambda map. With Fuel Closed Loop turned off, the Main Fuel map values can then be gradually adjusted so that less (or ideally no) correction is required. Closed loop control can then be turned back on and the smaller correction requirements should then be observed.