injectors take less time for the injector to fully open once the injector driver fires. According to SAE
recommended practice (spec. J1832), high impedance injectors are typically non-linear (as a result of the
response time) when operated below about 1.8 milliseconds, while low impedance injectors are non-linear
below about 1.6ms.
In practice, low impedance injectors can be controlled down to about 1.3ms reliably, while high
impedance injectors generally require 1.5ms or higher pulsewidths. These characteristics have a big effect
on idle quality on engines with large injectors. If the injector cannot physically be pulsed less than 1.3ms,
and the engine is still idling too rich, there is no way to reduce the fuel flow by decreasing the injector
pulse width. Instead, either a smaller injector must be chosen, or a rising rate fuel pressure regulator must
be used. Alternatively, a set of staged injectors can be installed, which would allow a smaller set of
primary injectors to be utilized. Another option would be to switch to a full sequential setup, which would
require the installation of a camshaft reference pulse for TDC #1.
D.2. Injector Firing Schemes
Most engines will operate quite well using a phase-sequential injector firing mode. This firing mode
pairs injectors together just like the waste-spark coil firing scheme. On a standard inline 4-cylinder four-
stroke engine, cylinders 1 and 4 will always be on top dead center at the same time, but one cylinder will be
on compression when the other is on exhaust. The same hold true for cylinders 2 and 3. As a result, it is
possible to use just two injector channels to drive four low (or high) impedance injectors for this engine:
simply pair the injectors for cylinders 1 and 4 to channel 1, and the injectors for cylinders 2 and 3 to
channel 2. If a phase-sequential firing scheme is chosen in the software, each channel will fire once per
revolution. This means that each cylinder will receive a pulse of fuel twice per engine cycle (once per
revolution on a 4-stroke). This type of firing scheme requires only the standard Electromotive 60(-2) tooth
trigger wheel on the crankshaft. No cam sensor is required. For an outline of the various firing options
available with the
TECgt
, see the tables in Section C.3.
•
Regardless of engine firing order, the
TECgt
fires its injector output channels in numerical order 1-
2-3-4-5-6. Injector channels must be wired appropriately to match an engine’s firing order.
•
If an injection mode does not use all six output channels, it will reset after its intended number of
channels have fired. As an example, a 4-cylinder phase-sequential setup will fire 1-2-1-2-1-2-etc.
The remaining channels are reserved for staged injectors, and are keyed to channels 1 and 2,
respectively.
As can be seen in
Section C.3
, we have accounted for most injection scenarios. If your desired
injector firing scenario is not listed, it is advised that you call Electromotive Technical Support. Some
definitions concerning the language used in
Section C.3
are given in sections C.2.a. through C.2.e.
D.2.a. Staged Injection
An injection layout whereby there are “primary” and “secondary” injectors. The primary injectors
would be sized such that the engine will idle nicely, while the secondary injectors would supply additional
fuel needed for high-rpm, high-load situations. Most rotary applications utilize this injection method, since
there would otherwise only be one injector per rotor for idling and high-load conditions. On a two-rotor
engine with 400HP, at least a 120 lb/hr injector would be needed for each rotor, if only one injector were to
be installed. However, with this injector in place, the engine would not be able to idle at a normal RPM,
since the injector would be supplying far too much fuel, even with the shortest possible pulse width. To
avoid this problem, 55 lb/hr primary and 100 lb/hr secondary injectors could be used. Piston engines with
very high rpm power bands (like motorcycle engines) can also benefit from staged injection for the same
reasons as the rotary example. Staged injection can be used with sequential, phased sequential, and TBI
firing schemes. The WinTec software dedicates the unused injector channels for each setup for staged
injectors.
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TECgt Manual Version 2.0
- Page 52 -
©2008 Electromotive, Inc.
