SDS Map

The maps used by the SDS EFI/EI system, are used by the Engine Control Unit(s) (ECUs) to control how the engine operates.

Below I will walk through the map used to control my Lycoming IO-540 engine with 9:1 compression pistons and Barret Precision Engines cold air induction system. As always, the info below represents what I use and explains the rationale used in determining various values. When looking at the map pdf, the values in green or yellow represent values changed after engine break-in.

Typically, you will not need to change any SDS supplied map values during engine break-in. Once break-in is complete, you may adjust the map required to achieve optimal engine performance. See the Engine Tuning page for details on how this may be accomplished.

Readers are cautioned that in all cases documentation contained on the SDSEFI.COM website always takes precedence over anything on this website. The map below is what I use, it may not be suitable for your purposes. Readers use this information at their own risk.

The map controls engine operation under various operating conditions. Note that the table contains values up to 4500 RPM. However, my IO-540 is governed never to exceed 2700 RPM. Consequently values higher than 2700 RPM are never used.

The map data table is too large to reasonable display on a webpage. You may view and/or print a PDF copy of my map here. I suggest you print it and refer to it when reading the details below. Note that this map is for the PRIMARY ECU except that I have also displayed the Trim values for Cyl #4, 5 & 6 which are stored in the secondary ECU.

The PDF values in yellow / green / blue represent values I have changed on various separate occasions. By highlighting, I can easily identify what I have changed and when.

I also suggest you review the values stored in your ECU. Here is a the Excel spreadsheet (with my values) that you can use to record your ECU values. Download Excel map. Be sure to check the values in the primary and secondary ECU. Aside from a few exceptions noted below, the values should be identical. Contact SDS if you are uncertain about anything in you map.

The base values used in my table were provided by SDS with my ECU in 2019 and were then modified, in some cases, to suit my needs. Since then SDS supplied base values may have changed so keep this in mind when reading below. Always consult with SDS if you are unsure as to what changes are to be made.

The map values are entered by using the SDS programmer shown to right.

Please note that except for the Timing Magnet positions and the fuel trim values, the PRIMARY and SCONDAY MAPS MUST BE IDENTICAL. If you change a value in one ECU, be sure to make the corresponding change in the other. Failure to do so can cause problems.

Key To The SDS Map

RPM/Fuel Factor

The first major element of my table controls fuel flow based on engine RPM. Your will see a FUEL FACTOR associated with each engine RPM value in 100 RPM increments. In each case the factor is 140 except for 2600 and 2700 RPM. For these values, the factor becomes 231. The increase at high RPM reflects the need for additional fuel at high power settings. By increasing fuel using the MAP, there is typically no need to manually enrich the engine during take-off. The 140 fuel factor represents what is necessary during normal cruise operations.

I modified these values when tuning my engine AFTER break-in. However, during break-in, I manually varied the mixture to control CHTs and to ensure the engine was receiving sufficient fuel for take-off.

Manifold Pressure / Fuel Factor

These table entries adjust fuel flow based on the selected manifold pressure. You will notice that except for the first two entries, the fuel factor increases as manifold pressure increases. This is logical as higher manifold pressures require more fuel to make the increased power demand.

The first two entries in the this table typically come into play only when there is a Manifold Atmospheric Pressure sensor (MAP) failure. If the MAP Sensor fails, the ECU will fuel at near full throttle levels as a safety measure. It is essential to keep to keep the engine operating if the MAP sensor fails.

Readers are cautioned to never change low RPM / low manifold pressure values as these values are essential too keep the engine operating in the event of a MAP sensor failure. See the SDS Lycoming Tuning Guide for more details.

These factors used were not changed.

Engine Temp / Fuel Factor

These table entries are usually only used to increase fuel to the engine when the engine is cold. You will note that as the temperature of the engine increases, the fuel adjustment tapers off. Once the engine is at normal operating temperatures (176F and above), the factor goes to zero.

The factors used were not changed.

Start Temp / Fuel Factor

These table entries are usually only used to increase fuel to the engine when starting based on the engine temperature. When the engine is hot, there is little adjustment.

The factors used were not changed.

RPM / Ignition Timing

This table determines the engine timing in degrees before top dead center (BTDC). At lower RPMs, the timing is reduced to allow better combustion of fuel – slower RPMs mean there is more time for fuel to burn so ignition can be delayed somewhat. At normal cruise RPMs (at or over 1500 RPM), the timing becomes 24 degrees BTDC which is the recommended value for my engine. It is what would be used if magnetos were installed.

The factors used were not changed.

IGN RET-ADV/LOAD

These factors allow ignition timing to be changed through a range of Manifold Pressures. In my case I do not use these table entries. In my opinion, there is no need to use these values as my timing is optimally set when cruising at 2400 RPM regardless of what Manifold Pressure is being used / achieved. By setting these values to zero, engine tuning is also simplified – particularly tuning for Lean of Peak (LOP) operations.

All values set to zero.

Air / Temp

The Air / Temperature factors adjust fuel based on the Outside Air Temperature (OAT) measured by the ECU OAT sensors. As air becomes colder, it’s becomes denser and therefore more fuel is required to maintain the desired Air/Fuel ratio.

No change was made to these values.

Other Single Entry Values

There are a number of other values that can be set using the SDS programmer. The values below represent the parameters that were available in my ECU as of 2022. Future changes to the ECUs will likely introduce new parameters not reflected below.

Always consult SDS documentation before changing any of these parameters. Incorrect parameters can cause serious problems.

In almost all cases these values will be set by SDS and should never be changed. Usually you will only want to change the:

• Fuel Trim Parameters for Cyl # 1 to 6
• Lean with Pin 13 / Ign Advance Switch (% fuel change when LOP)
• Pin 13 Aux Input Advance Switch, Most people use use LOP button on programmer to activate.
• Advance Switch which specifies ignition advance when running LOP