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The principle of electronic fuel injection is very simple. Injectors
are opened not by the pressure of the fuel in the delivery lines, but
by solenoids operated by an electronic control unit. Since the fuel
has no resistance to overcome, other than insignificant friction
losses, the pump pressure can be set at very low values, consistent
with the limits of obtaining full atomization with the type of
injectors used. The amount of fuel to be injected is determined by
the control unit on the basis of information fed into it about the
engine's operating conditions. This information will include manifold
pressure, accelerator enrichment, cold-start requirements, idling
conditions, outside temperature and barometric pressure. The systems
work with constant pressure and with "variable timed" or "continuous
flow" injection. Compared with mechanical injection systems, the
electronic fuel injection has an impressive set of advantages. It has
fewer moving parts, no need for ultra-precise machining standards,
quieter operation, less power loss, a low electrical requirement, no
need for special pump drives, no critical fuel filtration
requirements, no surges or pulsations in the fuel line and finally,
the clincher for many car makers, lower cost.
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