Manual

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APPENDIX B FUEL INJECTORS
This Appendix covers issues relevant to Injectors and their use with the F10 ECU.
B.1 Injecto r Impe da nce
Electrically, there are two different typ es of electronic fuel injectors:
Saturation
Saturation injectors have a high coil impedance (> 12Ω) and are co mmon in average
production cars. Saturation injectors, require a simple switch to operate. When a 16
ohm injector has 12V applied across its terminals, ultimately the current 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 maximum current or is “saturated” (0.75 A). The
coils remain in saturation until power is switched off at the end of injection.
Peak-and-Hold
Peak and Hold injectors gen erally have a low coils imp edance (< 6Ω) and ar e mor e
common in motor-sp ort app lications. In Peak-and-Hold injectors the coil imp edance
is reduced in order to reduce the injector opening time. If these injectors were allowed
to remain saturated high continuous currents would flow resulting in a great deal of
heat and wasted energy . A much smaller current is needed to hold the injector op en
than is needed to initially switch it on, because of this p eak-and-hold injectors operate
in two modes as their name suggests: 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 en gin es needin g lar ge fu el-flow rates.
Peak-and-hold injectors come with a wide variety of current requirements. M ost 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.
B.2 The F10 Injector Drive rs
The solid state devices within the F10 ECU that are used to switch the injectors are known as
the injector drivers.
- The F10 and F10A have 4 heavy-duty injector drivers.
- The F10-8 and F10A-8 have 8 heavy-duty injector drivers.
Each individu al driv er limits its current draw to 4 amp s, and, upon reachin g that limit, clamps
the current to just 1 amp.
The drivers used in the F10 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. M ost high
current motors-port injectors can also be fired (one per driver) providing fuel pressures are not