Haltech E6S - Manual (Page 106)

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Appendix C
Injector Impedance
Electrically, there are two different types of electronic fuel injectors. One type of injector,
characterised by a high coil impedance (> 12
Ω
) is known as saturation injectors. The other
sort of injector, typically with coils of less than 6 ohms impedance, is known as peak-and-
hold injectors. The names are derived from the current waveform that accompanies the
injector when it is switched on.
Saturation, or high impedance, injectors, require a simple switch to operate. When a 16 ohm
injector has 12V applied to it, the current that is expected to be drawn is 0.75 amps (by Ohm's
law). However, the current in a coil cannot change instantly. When power is applied to this
injector, the current builds in the coil over a period of around half a millisecond, until it
reaches its 0.75 Amp maximum, i.e. saturation. The coils remain in saturation until power is
switched off at the end of injection.
In order to reduce opening time, the coil impedance can be reduced. Very low impedance
would result in very large continuous currents, resulting in a great deal of heat and waste of
energy. However, a much smaller current is needed to hold the injector open than is needed to
initially switch it on. Thus, such an injector is described by two currents: a peak current for
opening, and a hold current for maintaining the fuel flow. These peak-and-hold, or low
impedance, injectors, are particularly good for high rpm engines needing large fuel-flow rates.
Peak-and-hold injectors come with a wide variety of current requirements. Most peak-and-
hold injectors need 2A to switch on with 0.5A hold current (2/0.5A peak-and-hold), or are
4/1A peak-and-hold. Some very high performance injectors need as much as 6A to switch on,
especially under high fuel pressures.
C.1 The E6S Injector Drivers
The solid state devices within the E6S ECU that are used to switch the injectors are known as
the injector drivers. There are two different E6S models: E6S and E6S8. The E6S possesses
four heavy-duty injector drivers. The E6S8 has eight injector drivers (4 extra drivers in
parallel with the standard E6S injector drivers). Both models can use either saturation or peak-
and-hold injectors. Each individual driver limits its current draw to 4 amps, and, upon
reaching that limit, clamps the current to just 1 amp.
The drivers used in the E6S and E6S8 are each capable of firing two saturation injectors.
Thus, the E6S with four drivers can use a total of eight injectors. Individual drivers are
capable of firing one or two 2/0.5A peak-and-hold injectors. If using 4/1A peak-and-hold
injectors, you should not employ more than one injector per driver. Most high current
motorsport injectors can also be fired (one per driver) providing fuel pressures are not