Specifications

Engine Management and Data Acquisition SystemsPage 70
MoTeC Glossary
Description of terms specific to EFI Industry
Sequential Fuel Injection
Sequential means that each injector for each cylinder is triggered only one time during the engine’s cycle. Typically the injector is triggered only during
the intake stroke. True sequential injection requires the ECU to know not only where top dead center is, but also which half of the cycle the engine
is on. TDC on a 4 stroke occurs 2 times during the cycle, once on compression and once on exhaust. MoTeC references all timing events that occur
within the ECU, to Top Dead Center Compression. is generally requires an input on the engine’s camshaft to provide the ECU with a SYNC signal.
Once the ECU is synched, injection timing can be optimized to provide the most efficient mixing of fuel and air into the cylinder. Control of injection
timing can lead to increases in midrange torque while decreasing emissions and fuel consumption.
Semi-Sequential Fuel Injection
Semi-Sequential means that 2 or more cylinder’s injectors are triggered at the same time, but only 1 time during the engine’s cycle. is requires the
ECU to be synched with the engine’s cycle. Typically injection timing is retarded from the optimum timing point for full sequential by an angle which
is equal to 1/2 the angle between 2 cylinders in crankshaft degrees. On a V8 Chevrolet, the injectors for cylinders 1 and 8 would be triggered at the
same time. ey would be triggered 45 degrees late for cylinder number 1 and 45 degrees early for cylinder number 8. Degrees between 1 and 8 = 90
; 1/2 of 90 = 45. Semi-sequential allows optimization of injection timing which typically leads to increases in midrange torque and a reduction in fuel
consumption for equivalent power compared which Batch fire.
Injection Timing
With a synced engine which uses 1 injector in each intake manifold runner, it is possible to phase the firing of the injector so that it only sprays during
the intake stroke. is allows you to introduce fuel into the intake stream precisely at the time when the airflow into the cylinder is the greatest provid-
ing the best possible atomization and the highest efficiency. MoTeC offers a user definable 2 or 3 dimensional Injection Timing adjustment table so that
you can accurately match any engine’s injection timing demands. Tuners can select either beginning or end of injection on which to base the timing
table. is allows the tuner the ultimate in adjustability to suit any engine combination. With the M4 and M48 ECU’s Injection timing is adjustable in
5 degree increments while the M400/600/800 Series offer .1 degree resolution making them suitable for Gasoline or Diesel Direct Injection.
Batch Fire
Batch fire means that 2 or more injectors are triggered at the same time once every crankshaft revolution. If the ECU is synched with the engine’s cycle,
the injection timing can only be half optimized as fuel is injected both on the intake stroke and on the power stroke. Companion cylinders are paired in
batch fire mode similar to wasted spark ignition modes. e advantage of batch firing is that the ECU needs only to know where TDC is. is means
that a sync on the cam is not required. e disadvantage to batch firing is that the Injector Dead Time is doubled for the engine’s cycle. is leads to a
decrease in fuel flow and typically requires a larger, less efficient injector to be used to make up for the loss of flow. On High Horsepower applications
this means the idle quality will suffer tremendously.
Injector Dead Time
Injector dead time refers to the latency of the injector in producing maximum flow rate. All injectors require a certain amount of time to open com-
pletely and produce maximum flow. e amount of time is dependant on several variables including; fuel pressure, battery voltage and physical charac-
teristics of the injectors themselves. Typically higher fuel pressure or lower battery voltage tends to increase the dead time. is leads to a reduction in
fuel flow in to the engine and as a result influences the engine’s state of tune. Luckily MoTeC allows the user to define an injector Dead Time table if
the values are known, or use a standard compensation which is known for a number of injectors. e ECU automatically adjusts the values as the bat-
tery voltage changes to ensure that the fuel curve remains constant. If a fuel pressure input is used on the system, MoTeC can compensate for variations
in fuel pressure to achieve a consistent fueling even with varying fuel pressures.