[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [New Search]
I found this on the 510 list and I thought it might behelpful in
explaining Fuel Injection to someone that didn't quite understand it?
Jason Renville
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I would rather attempt something great and
Fail than attempt nothing and succeed.
Jason_Renville@ccm.al.intel.com
69 Fastback second owner.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
______________________________ Forward Header __________________________________
Subject: About Fuel Injection Systems (Long)
Author: daemon@hpcvts.cv.hp.com at SMTPGATE
Date: 3/21/97 8:35 PM
<snip>
Fuel Injection Systems
Types:
Mechanical:
This system is as it's name implies is purely mechanical. The Throttle cable
is connected to the throttle plate as well as the injection system. A cam in
the injector body changes the air/fuel ratio base on RPM and Throttle
position. These systems are very difficult to modify. A new cam must be
ground to match the fuel requirements of if your motor has been substantially
modified. Mechanical system are typically found on Italian Cars.
Continuous Injection System (CIS)-
It is an electro-mechanical system which as it name states supplies a
continuous injection of fuel. The rate at which the fuel is injected is
varied though various inputs such as airflow, throttle position, RPM and
engine temperature. This system is not optimum for performance modifications
as it is difficult to provide additional fuel flow especially at high RPM,
when radical cam or other modification are made. Increasing the available
fuel flow requires changing the Valve Body. This is a system commonly found
in Early Injected VW Rabbits, Mercedes and Other European cars.
Electronic Fuel Injection (EFI)- The uses a computer to control fuel
metering.
Found on 99% of all cars sold in the US.
Types of EFI-
Throttle body fuel injection (TBI)- Injection of fuel at throttle plates
This was one of the earliest systems used by American Manufacturers and some
foreign. The system typically consists of an injection system placed where
the Carburetor would normally be placed. (It was much cheaper put it where
the carb was rather that make a new intake manifold.) Just about all the
fuel injection components were contained with in the throttle body- Flow
sensor, Throttle Position sensor (TPS) and injectors. TBI systems usually
contained 2 high flow injectors to provide fuel for all the cylinders.
Airflow, Throttle Position, temperature and RPM inputs are fed to the
Electronic Control Unit (ECU) and the fuel flow adjusted accordingly.
Multipoint/Port Fuel Injection-
Injectors are located in each of the intake ports. The injectors are
typically aimed at the back of the intake valve. Depending on injector
timing fuel may be injected while the valve is open. This type of system
typically provides the best throttle response.
Types of Mutipoint Injection
Sequential Injection: Injectors are fired in relation to the Firing order of
the motor.
Single Pulse Injection: Each Injector is fired once per two revolutions of
the motor, typically during the intake stroke. The HO Mustangs used a single
pulse system. Ford found that less atomized fuel produce more HP at a slight
SMOG penalty. (Less Common)
Dual Pulse: Injectors are fired once per revolution of the motor. Once
during Intake and once during compression (while the intake valve is closed).
This system give the fuel more time to atomize, resulting in better SMOG
emissions. (More common)
Types Mass Airflow Measurement:
The Measurement of air entering the engine, typically in Lbs/Hr.
Speed Density: Uses inputs from MAP, Throttle Position, RPM and Engine
Temperature sensors to "look up" fuel requirements on a multidimensional map
contained with in the ECU. Based on the map the fuel flow is adjusted
accordingly. Because this system does not actually measure the amount of air
entering the engine, it is the least accurate of the EFI systems, but it
still provides more accurate fuel metering than Carburetors. These systems
are very durable and are used in many racing and aftermarket systems. One of
the Electromotive systems is a Speed Density System if not all of them.
Vane: As the name states a vane is used to measure Airflow. A vane is place
across the intake stream and the displacement of the vane is measure. The
displacement of the vane correlates to the amount of Airflow into the engine.
As one can imagine the vane across the intake tract causes a slight
restriction in the airflow and therefore is not the optimum for performance.
Used on 280Z, 280ZX, 200SX and CIS systems. Also used on the system in
Kelvin's article.
Hot Wire: A platinum wire is strung across the intake airstream. A fixed
voltage is applied to the wire and it heats up. Platinum wire has the
inherent property of wanting to stay at fixed temperature. As air flow
passes over the wire it cools the wire. As the wire cools the resistance
goes down in relation to the amount of air and the current flowing across the
wire goes up to maintain the temperature. The amount the current changes is
a measure the Mass Flow of air entering the engine. These sensor are very
accurate. They are not effected by altitude or temperature. Any change in
altitude or temperature will result in a change in the Air Density, which in
turn changes the amount the wire is cooled there for compensating. These
sensors can be fragile much like the filament in a light bulb. Due to the
small area of the Filament there is very little restriction on air flow, thus
this sensor is better for performance than the Vane. Used on VG30's, I do
not know about VG30DE's.
Hot Film: These work on the same principle was the Hot wire but the platinum
is deposited on a Thin Film substrate, which is more durable than a Hot wire.
This style of sensor is becoming the current standard. Due to the small
cross-sectional area of the Film there is very little restriction on air
flow, thus this sensor is better for performance than the Vane. New GM and
Ford cars, Bosch's current Motronic system
Terms:
Close Loop System: The ECU receives feed back from an Oxygen sensor placed
in the exhaust tract. A measurement can then be made of the Air / Fuel Ratio
and the fuel injection adjusted for the optimum air / fuel ratio. Any car
with and O2 Sensor.
Pulse Width Modulated: The means in which electronic fuel injectors are
fired. Fuel injectors are fired by means of an electric signal. The
duration of the signal is the "Pulse Width". The longer the Pulse Width the
longer the injector stays open (i.e.. spraying fuel). Electronic Fuel
Injectors can not be left on 100% of time. They have a Duty Cycle. Flow
rates for injectors (Lb/Hr) are rated at 80% duty cycle at 40psi.
Components:
Electronic Control Unit (ECU): The computer which controls the Fuel
Injection and sometime the Ignition System.
Fuel Injector: Injects the fuel into the intake system. Injectors are sized
based on CFM of an engine, at it maximum RPM and 80% effeciency, divided by
the # of injectors.
Fuel Rail: A pressurized rail to which all the fuel injectors are attached.
Pressure Regulator: Attached to the Fuel Rail
Pressure regulators for EFI systems are very important, because Injectors are
rated using a constant pressure. They are connected to Manifold pressure and
adjust the fuel pressure to maintain an "Constant" pressure value in relation
to manifold. Pressure is adjusted based on Manifold Vacuum or Boost (w/
turbo charging). In other word under high manifold vacuum less pressure is
required to inject the same amount of fuel because it is being "Sucked" in.
The opposite applies for Turbo "Boost" conditions where more pressure is
required to inject the fuel because the manifold is pressurized.
Throttle Position Sensor (TPS): Measures the position of the Throttle
plate(s) and the rate at which the throttle plate was opened. This is used
to determine what type of load the motor is being subjected through.
example: Low RPM / High Load. The throttle plate(s) may be wide open, but
due to the low RPM air flow will also be low. This situation requires a
different air/fuel ratio as compared to the same Airflow but Higher RPM /
Light load with a slight throttle opening.
Oxygen Sensor: Used to measure the amount of O2 in the exhaust system. The
resulting measurement directly correlates to the Air/Fuel ratio.
Manifold/Atmospheric Pressure Sensor (MAP): A sensor which measures Manifold
Vacuum and Atmospheric pressure.
Idle Speed Control: A valve which adjusts to allow air to bypass the
Throttle plates to control Idle speed. Many new cars will Increase Idle
speed when axially items are turned on (i.e. AC and Alternators).
Exhaust Gas Recalculation (EGR) Valve: A valve which when open allow
controlled amounts of exhaust to flow back in to the intake system. Given
the Exhaust is mostly CO2 and Water it reduce the amount of Oxygen available
for combustion, therefore reducing combustion temperatures and Nitrous Oxide
production. The valve is often control by the ECU.
I hope this help.
Chris Ken
DAT510@aol.com