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Detroit has not produced a carbureted engine
since 1985. |
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Every automobile produced since has utilized
either a form of Multi-Point Fuel Injection (MPFI) or Throttle Body
Injection (TBI). |
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More torque and power |
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Intake manifold can be optimized with dry flow |
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Improved throttle response and drivability |
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No hesitation/stumble when cold |
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No vapor lock when hot |
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Better fuel economy |
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Mileage per CID has doubled over the past 20
years |
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Lower exhaust emissions |
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This preserves the environment for future
generations |
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Overall increase in engine lifetime |
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Decreased oil dilution results in less engine
wear |
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All of these improvements have been made
possible with the implementation of electronic engine management systems |
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Street Performance |
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Street Rods |
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“Pro Street” |
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Drag Racing |
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“Pro Mod” |
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Sportsman |
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Shootout |
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Marine |
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1962 Corvette
327CID, 360HP |
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All modern electronic fuel injection systems
work in essentially the same way. Many times a second, a handful of sensors
translate various physical conditions both inside and outside the engine
into electrical voltages which supply the Engine Control Unit (ECU) with
the same mixture requirement information that in a carburetor came merely
from the pressure differences. |
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The computer then converts the final calculation
into a timed voltage pulse which prompts the injector to open at a specific
time and for a specific duration. The injector electromagnetically pulls
back its internal tapered plug ("pintle"), and high pressure from
an electric pump upstream in the system forces fuel through one or more
holes whose incredibly small size causes the fuel to "fog",
making it more thoroughly vaporized and therefore more readily combustible. |
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Saturated Driver |
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Injector is switched on with full battery
voltage and allowed to saturate the injector coil for as long as injector
is open. |
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Peak/Hold Driver |
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Supplies full battery voltage to fuel injector
for rapid current rise, in order to produce positive injector opening. When load current reaches a preset
level, the driver reduces the load current and becomes a constant current
source. This condition holds the
injector open and reduces power dissipation. |
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8 low-impedance injectors saturated with 14
volts can draw in excess of 50 Amps! |
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8 low-impedance injectors operating with
Peak/Hold drivers will typically draw 8 Amps regardless of battery voltage. |
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Typical 4 Amp / 1 Amp Driver |
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Throttle Body Injection (TBI) |
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Port Fuel Injection (MPFI) |
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Direct Injection |
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Just as carburetors were replaced by port fuel
injection, direct injection will someday become the industry standard |
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Batch Fire / Simultaneous Double Fire (SDF) |
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Fires all injectors simultaneously, every 360
degrees |
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Bank to Bank |
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Fires injectors in alternating banks, every 180
degrees |
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Sequential |
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Fires each injector individually, in sequence,
once for every combustion event |
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BANK-TO-BANK ECU |
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Bank-to-Bank injection mode fires 2 injectors on
each bank every 180 degrees resulting in better fuel distribution due to
reduced fuel rail pressure fluctuations |
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Injects in programmable, prescribed firing
order, each injector firing once every 720 crankshaft degrees resulting in
the best fuel distribution possible with a minimum amount of fuel rail
pressure fluctuation. |
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Fuel Injector opening is synchronized to intake
valve opening |
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Alpha-N |
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Uses a combination of engine RPM and throttle
angle to determine air flow. |
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Speed/Density |
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Uses a combination of engine RPM and manifold
pressure to determine air flow. |
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Mass Air |
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Uses a flow sensing device such as a pivoting
vane or heated wire in intake tract to monitor mass flow of air into
engine. |
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ECU calculates Mass Air Flow using Engine
Displacement, RPM, Manifold Pressure, Manifold Air Temperature and
Volumetric Efficiency as factors. |
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ECU calculates Injector Pulse Width using Mass
Air Flow, RPM, Injector flow and Target A/F Ratio |
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The most common method of feedback control
for an electronically fuel injected engine is with the use of an O2
sensor which permits the system to compare the residual oxygen in the
exhaust with the amount in the outside air. This is called “closed loop”. |
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Open Loop does not utilize an O2
Sensor for making corrections to fuel delivery |
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Closed Loop does utilize an O2 Sensor
for corrections to fuel delivery |
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Only accurate at 14.7:1 Air/Fuel ratio |
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Good for closed loop operation at cruise |
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Not recommended for closed loop use at WOT |
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Allows for precise Air/Fuel ratio closed loop
operation over entire engine operating range |
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Can have the best of both worlds |
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Lean part throttle performance for fuel economy
and reduced emissions |
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Best power Air/Fuel ratio at WOT |
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Compatible with Alcohol fuels |
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Each sensor calibrated with a unique resistor
for high-precision Air/Fuel ratio monitoring and control |
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Wideband 02 sensor is accurate from 9:1 to 16:1 Air/Fuel ratio |
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Allows the tuner to trim the fuel delivery for
each cylinder, individually |
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Allows the tuner to trim the spark timing for
each cylinder, individually |
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Turbocharged 4-cylinder engine making over 800
HP |
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4 injectors will be used to supply 400 lbs of
fuel |
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Considerations: |
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Injector Selection |
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Fuel Pressure and Volume |
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Time Available to Inject in mS (TAI) |
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TAI=1000/(RPM/120) |
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Injector % Duty Cycle (InjDC) |
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InjDC=(InjMS*TAI)*100 |
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Fuel Flow in Lbs/Hr (FFLB) |
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FFLB=(NumCyl*InjFlow)*(InjDC/100) |
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Injector Sizing (BSFC Typically .5) |
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InjFlow=(Est. HP*BSFC)/NumCyl |
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Injector % Flow Change vs. Fuel Pressure |
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100*SQR(OldFP/NewFP) |
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Notes