Haltech E6M - Manual (Page 125)

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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
common type of injector, typically with a coil impedance of less than 6 ohms, is known as
peak-and-hold injectors. The names are derived from the current waveform that drives 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. These injectors can be 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 E6H/E6M Injector Drivers
The solid state devices within the E6H/E6M ECU that are used to switch the injectors are
known as the injector drivers. The E6H/E6M possesses four heavy-duty injector drivers and
the E6H-8/E6M-8 have Eight drivers. The ECU can drive either saturation or peak-and-hold
injectors. Each individual driver limits its current to 4 amps, and, upon reaching that limit,
clamps the current to just 1 amp.
The drivers used in the E6H/E6M 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 E6H/E6M model to choose contact your Haltech dealer for advice.