Page 4 of Fuel Injection by Holley Performance Products, Inc.

fuel injection technicalinform at i o n coolant temperature sensor the coolant temperature sensor is a two-wire sensor that is threaded into the engine block and is in direct contact with the coolant the function of this sensor is to generate a signal that the ecu uses to adjust the fueling levels required for the operation of the engine and operate ancillaries the thermistor contained in the sensor generates an electric signal that is proportional to the coolant temperature at low temperatures the resistance is high 3800 ohms generating a 5-volt signal in the ecu at normal engine operating temperatures the resistance of the sensor is low 180­200 ohms which generates 1­2 volt signal in the ecu other functions of the coolant temperature signal are · · · · · top-fed fuel injector when the ecu activates this electromagnetic valve the injector meters and atomizes fuel in front of the intake valve the fuel enters the top and is discharged via the metering orifice at the bottom at high pressure the spray geometry and cross sectional area is specific to the engine application in general there are four major spray patterns · · · idle speed adjustment via the iac modify spark advance electric cooling fan operation activation of the egr torque converter clutch application · pencil stream solid stream narrow angle spray split pencil stream two solid streams narrow angle sprays usually used in multi valve cylinder applications bend spray solid stream narrow angle spray being discharged in an angle with respect to the injector center axis this application is used in engine applications where the injector package does not allow alignment of the injector axis with the spray target center axis oblong spray this spray geometry consists of an elliptic or oblong cross-sectional area of the spray this application is used in engine applications where the spray target requires a specific spray pattern fuel injection oxygen sensor the oxygen sensor is located in the exhaust manifold and its function is to measure the oxygen content in the exhaust gases the sensor is an electrochemical cell which develops a voltage signal between its two electrodes that is proportional to the oxygen content in the exhaust gases the oxygen sensor adjusts and maintains an optimum air fuel mixture to control the exhaust emission and the fuel economy when the oxygen content in the exhaust is high due to a lean mixture the output voltage of the sensor is close to zero if the fuel air mixture is on the rich side the oxygen content in the exhaust is low and the output voltage of the sensor approaches 1.0 volts there are three types of oxygen sensors · · · one wire o2 sensor not heated three wire o2 sensor heated four wire o2 sensor heated bottom fed fuel injector this electromagnetic valve meters fuel into the intake manifold in proportion to the air flowing into the engine when the valve is energized the electromagnetic force generated by the solenoid lifts the pintle/ball from the seat fuel under pressure is then injected into the throttle body bore or the intake port the spray configuration is application dependent for throttle body injection a hollow conical spray is required while for port injection a narrow pencil stream is preferred to avoid wall wetting high impedance injectors most injectors can be divided into two major categories high impedance 12 to 16 ohms and low impedance 1.2 to 4.0 ohms the high impedance injectors are used with ecus that are designed with saturation drivers the advantage of using saturation drivers is that the currents running through the ecu circuits and the injectors are relatively low thus generating less heat the disadvantage of saturation drivers is that the driver has a slower response time which could affect the full utilization of such a system at very high engine rpm low impedance injectors the low impedance injectors are designed to be run with an ecu that employs peak and hold drivers also called current sensing or current limiting drivers the current ratio peak to hold is generally 4:1 and the most common drivers available are 4 a peak/1 a hold or 2 a peak 0.5a hold the peak current is generated to overcome the inertia of the closed valve and once the valve is open the driver cuts down to 1/4 of the peak current to hold the injector open until the end of the metering event low impedance injector designs are mostly used in high flow applications 140 www.holley.com

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