SDS EM-5-D - RPM Fuel and Manifold Pressure Tuning

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The fuel tuning has been written in the sequence that we recommend tuning the system. RPM FUEL
first, followed by Manifold Pressure, Acc pump, Engine Temp, Start, closed loop and fuel
cutoffs/limits.
The amount of fuel injected by the EM-5 is determined by the values in rpm fuel, manifold pressure,
acc pump, engine temperature, start, air temperature. Once, the engine is at full operating
temperature, the main values that determine the fuel mixture are RPM FUEL and Manifold Pressure.
Most of the Manifold Pressure values can be left at their factory settings when the RPM FUEL values
are set properly. RPM FUEL values are where programming should begin.
RPM Fuel
The rpm band is divided into 38 ranges, either 100 or 250 rpm apart. This parameter is where the
main fuel programming is done in SDS systems. The variables which ultimately determine the
RPM FUEL values are engine displacement, injector flow rate and volumetric efficiency of the engine.
Volumetric efficiency varies with RPM. As a result, RPM FUEL values will vary accordingly. If a richer
mixture is desired at certain RPM’s, the RPM FUEL value will need to be increased. There should not
be large changes in adjacent values in RPM Fuel, rather smooth transitions.
Your system has a base map entered for the recommended injector flow rate or for the injectors
included in your kit.
Often people have their RPM FUEL values incorrect and find themselves having to re-slope the entire
64 manifold pressure values, which can lead to further problems. When the RPM FUEL values are
setup correctly, the majority of manifold pressure values can be left unchanged, thus greatly
simplifying tuning of the engine.
If you double the RPM FUEL value, this will double the pulse width of the injector pulse. If you wanted
to make the mixture 10% richer then you would simply add 10% to the RPM FUEL value. Example:
RPM FUEL value was 100, and is then changed to 110. This would add 10% more fuel to the mixture.
It is important to note that the number of injections are doubled when the rpm is doubled
regardless of the values entered. See figure 4.
With V31+ software, the maximum RPM fuel value is 350 where prior versions maximum was 255.