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Fuel System

Fuel Injection Component Identification Glossary

AUXILIARY AIR VALVE
The auxiliary air valve opens a cross-sectional air bypass around the closed throttle blades to maintain an acceptable idle during cold engine operation. A precisely calibrated bi-metallic strip governs the cross-sectional area of an internal gate which meters the amount of extra air admitted to the engine during the warm-up period. The bi-metallic strip has its regulating time governed by the use of a ceramic heating element. The part is also known as Auxiliary Air Device, Auxiliary Air Regulator.

AIR FLOW SENSOR
The air flow sensor measures the volume of air drawn in by the engine, and actuates the control plunger of the fuel distributor. Air drawn into the engine, as determined by load and RPM, must pass through the air sensor cone. As the center plate rises proportionate to intake air volume, a specific and constant plunger lift will likewise occur. This part is also known as the Air Flow Meter, Vane Meter, or VAF (Vane Air Flow)

AIR MASS SENSOR
The Air Mass Sensor delivers an intake air mass dependent electrical signal to the vehicle ECU, as a measure of engine load. The ECU electronically interprets this ever-changing input voltage so as to continually optimize the fuel/air mixture. The incoming air mass, as controlled by engine load, passes over a thin platinum wire that is heated to maintain a constant temperature. As air mass throughput increases (greater load) more current is required to maintain wire temperature, resulting in an increased voltage signal. This device provides an instantaneous response to changes in air mass and also corrects for air temperature and altitude automatically. This part is also known as  AMM, LMM, or Mass Air Flow Sensor.

COLD START VALVE
The Cold Start Valve is used to provide additional fuel needed to overcome fuel condensation and additional friction present during cold engine start-up. Dependent upon, and operating in series with the thermo-time switch, this solenoid operated valve creates an atomized "swirl" mixture, which is injected directly into the intake manifold plenum. This part is also known as the "5th" Injector, Cold Start Injector, or Cold Start Device

ELECTRIC FUEL PUMP
The electric fuel pump creates a continual pressurized fuel supply of specific volume to a central fuel metering area.  The electric fuel pump is usually a roller cell design driven by a permanent magnet electric motor. Fuel is scavenged from the vehicle fuel tank and pressurized within cavities formed between the individual pump rollers. The pressurized fuel exits the outlet check valve as a direct result of the centrifugal sealing action created in the roller chamber during rotation. This part is also known as a high pressure pump, supply pump

ELECTRONIC CONTROL UNIT
The electronic control unit calculates the engine management control parameters based on data received from various sensors.  Responding to measured variables and sensor input, the control unit adjusts fuel delivery, (and in the case of Motronic and KE Motronic, the engine timing also) through its controlling output stage.   This part is also known as ECA (Electronic Control Assembly), ECU, ECM, Logic Module, Trigger Box

ENGINE TEMPERATURE SENSOR
The internal resistor of the temperature sensor decreases in electrical resistance as the engine warms. Engine temperature via this resistance value is reported to the ECU and used as a correction to the output stage (injector delivery, etc.).  This part is also known as CTS (Coolant Temperature Sensor), Temperature Sensor II.

FREQUENCY VALVE
The frequency valve optimizes the air/fuel ratio by controlling injector delivery, as governed by the oxygen sensor/lambda control unit. Pulsing in a manner similar to an electronic injector, this device changes fuel distributor lower chamber pressure as needed by bleeding off a small amount of fuel to control injector delivery quantity. This part is also known as the Timing Valve or Lambda Valve.

FUEL ACCUMULATOR
The Fuel Accumulator maintains fuel pressure in the system after shutoff, ensuring positive re-start characteristics.  A spring loaded diaphragm is compressed during pump operation. Upon shutoff, the spring pressure holds fuel pressure in the fuel system

FUEL DISTRIBUTOR
The fuel distributor meters and distributes to each port fuel injector the basic injection quantity.  The sensor plate position is transmitted to the control plunger, resulting in increased plunger lift in correspondence to intake air volume. Acting as a spool valve, the plunger progressively uncovers the metering slits, which control the basic volume of fuel out to the port injectors.

FUEL FILTERS
Fuel filters maintain the high degree of fuel cleanliness critical to proper fuel injection operation and component longevity. Fuel must pass through a paper element, a fibrous "fluff trap", and finally through a mesh strainer.

FUEL INJECTION VALVES (Solenoid Types)
The solenoid type fuel injection valve precisely meters fuel into the individual engine intake ports. Driven by the electronic control unit, the valve needle will lift within the solenoid body to deliver the predetermined fuel quantity. Replaceable O-ring seals are provided to limit vibration and leakage problems, and to ensure the characteristic good hot start characteristics

The Throttle Body Type Fuel Injection Valve is also a solenoid type injection valve.  Operating at high frequency, it precisely meters fuel into the intake manifold plenum.  When triggered by the electronic control unit, this throttle body mounted valve generates a cone shaped spray pattern through multiple radially arranged metering holes. Atomization is achieved by swirl and rebound action instead of pintle lift.

FUEL INJECTION VALVES (Continuous)
The Fuel Injection Valves used in K/KE systems continuously atomizes the fuel through oscillation of the internal valve needle. This fuel is delivered directly to the engine's intake port.  Although they perform no metering function, the volume of fuel delivered to each fuel injector is atomized as the injector valve spring attempts to press the needle against the seat. The resulting "chattering" occurring at all fuel delivery conditions creates excellent atomization characteristics

FUEL PRESSURE REGULATOR
The Fuel Pressure Regulator (EFI multi-port type) maintains required system specific fuel pressure in a differential relationship between fuel pressure and manifold vacuum. This device directs excess fuel back to the fuel tank.  A spring loaded diaphragm (assisted by a vacuum chamber opposite the fuel side) exerts a preset pressure on the incoming fuel flow, and by deflecting slightly to allow through-flow, assures precise fuel rail pressure. The vacuum chamber receives and responds quickly to the signal from the intake manifold.

FUEL PRESSURE REGULATOR (KE)
The Fuel Pressure Regulator (KE) maintains constant primary fuel pressure, and ensures that the fuel return line is closed upon shut-off.  The pump generated fuel pressure is regulated as it deflects a main central spring during operation. Excess fuel and return fuel from the fuel distributor are directed back to the fuel tank by this device. A precision internal seal promptly seals off return fuel at the instant of pump shut down

GLOW PLUG
Glow plugs are auxiliary starting devices for diesel engines which are needed because a cold diesel engine may not create the heat needed for combustion.  Whether manually or automatically activated, the glow plug heats the surrounding air within which fuel can combust during cold start conditions. In automotive diesel applications, the glow plugs project into a pre-chamber where the nozzle injects the diesel fuel.

IDLE CONTROL UNIT
The Idle Control Unit maintains specific engine idle speed requirements. By influencing engine timing digitally, this device maintains a preprogrammed idle characteristic.

IDLE SPEED STABILIZER
The idle speed stabilizer holds idle speed to a specified value, dependent on engine temperature, electrical load, and other variables. The idle speed stabilizer continually adjusts a bypass opening around the closed throttle plate by rotating its open window in accordance with the dwell signal provided by the electronic control unit. This part is also known as Rotary Idle Actuator, Constant Idle Regulator, Idle Air Control (IAC), Idle Speed Compensator (ISC) and Idle Speed Regulator (ISR).

INJECTOR/PRESSURE REGULATOR SEALS
These flexible rings prevent unmetered air from entering the engine, position the injection valve, and prevent fuel leakage.  Depending upon system design, the injector seal is positioned on the injection valve so as to provide a leak-proof seal between the injector and the intake manifold. In many electronic fuel injection systems, an additional seal is fitted between the injector and fuel rail. The pressure regulator seal is utilized at the junction of the pressure regulator and fuel rail to prevent fuel leakage.

KNOCK SENSOR
The knock sensor detects potentially harmful detonation and sends this information electrically to the ECU.  The vibration caused by detonation compresses the crystal inside the knock sensor, resulting in a momentary voltage. In Motronic, the ECU uses this signal to retard the timing as necessary. Also known as the Detonation Sensor.

NOZZLE
The diesel nozzle atomizes and delivers diesel fuel into the combustion chamber area. The nozzle is positioned within the nozzle holder assembly; injecting fuel as the pintle is lifted against the force of the pressure spring. The nozzle body and pintle are manufactured as a precisely matched pair to ensure accurate fuel delivery.

OXYGEN SENSOR/ LAMBDA SENSOR
Oxygen sensors continuously monitor the exhaust gas oxygen content to maintain the ideal fuel/air ratio, which allows for proper catalytic converter operation.  A voltage signal, proportionate to the difference between exhaust gas oxygen content and that of outside air, is generated by the oxygen sensor and sent to the control unit. The ECU measures the electrical switching points of oxygen sensor voltage as exhaust gas oxygen content changes.

OVERRUN CUTOFF VALVE
The Overrun Cutoff Valve curtails fuel delivery during coasting/deceleration conditions.  The overrun cutoff valve will direct excess air into the intake manifold to stop fuel delivery when conditions of closed throttle, warm engine, and engine speed over a preset rpm are met (either coasting or decelerating). This part is also known as the Decel Valve or Coasting Cutoff Valve

PRESSURE DAMPER
This device smoothes pressure peaks created by the electric fuel pump, that might otherwise result in noise. The pressure damper is a spring-loaded diaphragm chamber that responds to dampen fuel pressure fluctuation. The pressure damper is either fuel pump or fuel rail mounted

PRESSURE SENSOR
The pressure sensor acts as an input to the electronic control unit to correct fuel delivery as a function of atmospheric pressure. Operating electronically, the pressure sensor sends a varying voltage signal to the electronic control unit in response to changes in outside pressure. Used as an additive correction, the control unit optimizes fuel delivery in response to changing atmospheric pressure. This part is also known as an Altitude Sensor.

RELAY
The Relay provides electrical power to the engine management system and provides a safety circuit to prevent fuel flow when the engine is not running. A primary ignition signal is most often used as an input to the relay which, when energized, provides power to the fuel pump, ECU, and the heated oxygen sensor if so equipped.

RESISTOR UNIT
The Resistor Unit reduces the voltage supplied to the port fuel injectors.  Battery voltage, supplied to the port injectors continuously when the vehicle is running, is reduced by the Resistor Unit prior to reaching the injection valves. Only certain L-Jetronic port injectors are designed to operate on this reduced voltage.  Also known as  Dropping Resistors, Ballast Pack, Resistor Pack.

RPM AND REFERENCE MARK SENSORS
The RPM and Reference Mark Sensors determine engine RPM and crankshaft angle, which are used by the Motronic ECU to optimize timing/fuel delivery, in addition to other related functions. Installed tangent to the flywheel, these sensors generate a voltage by induction, providing exceptionally accurate RPM and TDC information via a shielded cable to the ECU.

THERMO-TIME SWITCH
The Thermo-Time Switch completes the electrical circuit for, and limits the duration of, the cold start valve operation. An internal bi-metallic strip, heated both electrically and via engine heat, determines cold start valve on time by providing a short duration electrical ground.

THROTTLE POSITION POTENTIOMETER
The Throttle Position Potentiometer provides transitional load signal to the electronic control unit to allow for adjustment of engine management control. Identical to the throttle valve switch in basic mechanical function, this device substitutes a continuously varying electrical output signal for that of a switching function, therefore providing throttle position dependent engine control corrections

THROTTLE VALVE SWITCH
The Throttle Valve Switch communicates idle and full load position to the electronic control unit to allow for adjustment in engine management control.  Actuated by the throttle shaft, one set of contacts closes at idle with another signaling full-load electronically; all dependent on throttle position. Normally, the idle contact assists the overrun fuel cutoff and the idle speed actuator in controlling functions, while the full-load contact acts to signal need for additional fuel under wide open throttle.  Also known as Throttle Switch and Load switch.

TRIGGER CONTACTS WITH HOLDER
The Trigger Contacts with Holder provide the D-Jetronic ECU with a reference pivot for pulsing the port injectors.  Attached to the base section of the ignition distributor, the trigger contacts are actuated by a distributor shaft cam. The electrical interruption at the contact points triggers the ECU to actuate the port injectors.  This part is also known as Trigger Points

VACUUM LIMITED
The Vacuum Limited device provides additional air to the engine during transitional/closed throttle positions to maintain combustion.  When a specific difference in pressure before and after the throttle valve is achieved (as in deceleration) this valve opens to supply additional air to the engine.

WARM-UP REGULATOR
The Warm-Up Regulator provides additional after-start and warm-up fuel enrichment by reducing control pressure a specific amount for an "on-time" period determined by engine temperature. Utilizing a diaphragm-type valve activated by an electrically heated bi-metallic spring, the warm-up regulator varies the fuel pressure on top of the control plunger in the fuel distributor as needed. This part is also known as the  Control Pressure Regulator.

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