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Basically, an electronic fuel injection system (EFI)
works by delivering high pressure fuel to an electrically operated
valve called an injector. Where the electronic wizardry comes in,
is delivering the right amount of fuel, at precisely the right time
for every engine operating condition, across the rev range.
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The electronic control unit (ECU) receives information from a variety
of sensors, in and around the engine and makes the appropriate adjustments
to fuel delivery to maintain perfect, preset air/fuel ratios.
The problem with original equipment EFI is that reprogramming for nonstandard
applications involved creating a new chip for the ECU, a process beyond
the capabilities of most engine tuners. Even if a modified chip was available
commercially, it was still not possible to “tune” the injection
system for further engine modifications. In the late 1980s a number of
programmable aftermarket injection system ECUs arrived in the US, such
as those manufactured by 034EFI,
AEM,
DFI (Accel),
Electromotive,
Felpro
(FAST), Haltech,
Hondata, Link,
MoTeC, OnTronic
32-bit Fuel Injection, SDS,
Split Second, and
Wolf. These
systems can be programmed “on line” by connecting them to an
IBM-type personal computer. They allow the tuner access to the fuel maps
for idle, transition, wide open throttle, cold start, turbo boost enrichment,
and in some cases, ignition timing.
Tim Suddard, owner and editor of Grassroots
Motorsport Magazine, writing in an article about EFI states the
following major advantages:
- The extreme accuracy of fuel delivery by the ECU, at any load or RPM,
provides the engine with air/fuel mixtures that fall within a tiny window
of accuracy required for maximum power, or maximum economy.
- EFI systems are not subject to the usual fuel surge and frothing associated
with floats and float bowls in carburetors. One of the limiting factors
in race car lap times has been the ability of the fuel system to deal
with G forces. Gravitational forces in both horizontal and vertical
planes have no effect on EFI systems.
- ECU control of air/fuel ratios allows racing engines to safely operate
nearer to the “ragged edge”.
- PC programmable EFI can easily be adapted to suit future engine modifications
as a vehicle evolves. Adjustments to fuel and ignition curves being
as simple as making a few keystrokes on a PC.
- EFI generally permits greater flexibility of intake manifolds designed
to achieve higher inlet air flow rates and consistent cylinder to cylinder
air/fuel distribution.
- More efficient, higher compression ratios are usable, due to accurate
fuel metering. This is especially the case with EFI units incorporating
ignition control.
- When converting to forced induction, turbocharging, or supercharging,
EFI will enable the user to program boost-relative enrichment easily,
usually leading to substantial power increases as a result of accurate
fuel delivery.
- Most EFI systems compensate automatically for changes in altitude
and ambient temperature. Calibrating a fuel system for a specific race
venue is hardly necessary with EFI, if adjustments are to be made, a
few keystrokes on a PC are all that is necessary.
- Some EFI systems also have a provision for a cockpit-mounted mixture
control with which the driver can vary the air/fuel ratio. TWM's HALMETER
AF30 is particularly useful for this purpose, providing
a visual, onboard read out of the air/fuel ratio with its 30 LED display.
- The solid state electronics in EFI systems are not susceptible to
the mechanical failures associated with carburetors. Tuning parameters
remain as programmed, with never any need to adjust for wear.
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