Haltech E6K - Manual (Page 127)

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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 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 E6K Injector Drivers
The solid state devices within the E6K ECU that are used to switch the injectors are known as
the injector drivers. The E6K possesses eight heavy-duty injector drivers and 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 E6K are each capable of firing two saturation 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
excessive (>5 Bar). Running two high current, low impedance injectors from one driver can
result in difficulty in obtaining stable air:fuel ratios when injection times are short (around
idle and light load).
In general, an injector driver will reliably fire two injectors with more than 2.5 ohms coil
resistance. Coil resistance can be measured with an ordinary low-ohm resistance meter. If you
are unsure which E6K model to choose contact your Haltech dealer for advice.