Know U R wheelZ-MPFI

Now a days each n every vehicle is comoing with MPFI.Multi Port Fuel injection where electronic solenoid is used to inject the fuel at correct propotion and required air fuel mixture is injected.

Several injection systems are there and MPFI provide better performance and fuel economy when compared other systems. In the multi point fuel injection system an injector is located in the intake manifold passage. The fuel is supplied to the injectors via a fuel rail in the case of top fed fuel injectors and via a fuel gallery in the intake manifold in the case of bottom fed fuel injectors. Most of the MPFI systems use one injector per cylinder but in certain applications up to two injectors per cylinder is used to supply the required fuel for the engine.

This system injects fuel into individual cylinders, based on commands from the ‘on board engine management system computer’ – popularly known as the Engine Control Unit/ECU.Depending on the system encountered the injectors can fire either once or twice per cycle. ECU collect various information from various sensors placed all over the vehicle and calculate the correct proportion of AFR.

Various sensors used....

MASS AIRFLOW SENSOR (MAF):
  The mass air flow sensor is positioned in the air intake duct or manifold and measures the mass of incoming air. From this acquired data the ECU calculates the required fuel for the specific air mass flow rate. The MAF works on the hot wire or hot film concept. The hot wire/film is maintained at a constant calibrated temperature. The passing air cools down the hot wire/film and the added energy required to maintain the calibrated temperature is directly proportional to the mass of air passing by the hot wire. The MAF also compensates for humidity as humid air, denser or cooler, absorbs more heat from the sensor, requiring more current to maintain the calibration temperature.  

THROTTLE POSITION SENSOR (TPS) 
 

The TPS is a three-wire sensor that is mounted on the throttle body assembly and is actuated by the throttle shaft. The TPS is basically a variable resistor (potentiometer) that sends a voltage signal to the ECU that is proportional to the throttle shaft rotation. When the throttle shaft is open the sensor emits a high voltage signal and when the throttle shaft is closed it emits a low voltage signal. The voltage signal from the TPS changes between 0.45 V at idle to 4.5 to 5.0V at wide open throttle.

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. 

ELECTRONIC COOLANT TEMPERATURE SENSOR (ECT):
 

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 generating a 5-volt signal in the ECU.At normal engine operating temperatures the resistance of the sensor is low (180–200 ohms) which generates 1–2 volt signal in the ECU. 
CRANK SHAFT POSITION SENSOR (CKP):
 

Crankshaft position sensor is used to detect engine speed/ engine rotation position. They allow the ECU to change the injector opening; spark timing in various engine conditions The Crankshaft Position (CKP) sensor system consists of a CKP sensor plate and a pickup coil. The sensor plate has 34 teeth and is installed on the crankshaft. The pickup coil is made of an iron core and a magnet. The sensor plate rotates and, as each tooth passes through the pickup coil, a pulse signal is created. The pickup coil generates 34 signals per engine revolution. Based on these signals, the ECM calculates the crankshaft position and engine RPM. Using these calculations, the fuel injection time and ignition timing are controlled.

IDLE SPEED CONTROL ACTUATOR (ISC)
 

The IAC is located in the throttle body of the TBI, MPFI and CMFI systems. The valve consists of a stepper motor that adjusts the position of its pintle to vary the bypass air during idle and off idle conditions. During the closed throttle condition (idle), the ECU constantly compares actual engine speed with the programmed desired engine speeds. Discrepancy between these two values result in activation of the stepper motor increasing or decreasing the bypass air around the throttle plate(s) until desired engine speed is achieved. 

Inputs collected from these sensors are sent to ECU and it do rest of the works...

ELECTRONIC CONTROL UNIT (ECU) 
   

 The function of the ECU is to “tweak” or “fine tune” the engine operation to obtain the most complete and efficient combustion process. The ECU microprocessor receives input signals from various sensors from the engine which were discussed above and generates specific outputs to maintain optimum engine performance. The engine operating modes controlled by the ECU is the following:
• Cold and hot start
• Acceleration enrichment
• Battery voltage compensation
• Deceleration cut/off 
• Run mode (open loop or closed loop)
OPEN LOOP — Open loop defines the engine operation where the fueling level is calculated by the ECU with only the input signals from the throttle position sensor (TPS), from the coolant and/or air charge temperature, and from the manifold absolute pressure (MAP) or the mass air flow sensor (MAF).
CLOSED LOOP — Closed loop defines the engine operation where the fueling level is calculated and corrected by the ECU based on the voltage signal from the O2 sensor. When the O2 sensor emits a voltage signal above 0.45V due to a rich mixture in the exhaust manifold, the ECU reduces the fueling level by reducing the pulse width of the injector. The O2 sensor voltage is the feedback that modifies the fuel control program
that is based on other signals.

BASIC FUNCTION:
The process of determining the amount of fuel, and its delivery into the engine, are known as fuel metering. Modern systems are nearly all electronic, and use an electronic solenoid (the injector) to inject the fuel. An electronic engine control unit calculates the mass of fuel to inject. The ‘on-board’ ECU primarily controls the Ignition Timing and quantity of fuel to be injected. The latter is achieved by means of controlling the ‘duration’ for which the Injector solenoid valve coil is kept energized – popularly known as the ‘pulse-width’
  The mass airflow sensor senses the mass of the air that flows past it, giving the computer an accurate idea of how much air is entering the engine. The next component in line is the Throttle Body. The throttle body has a throttle position sensor mounted onto it, typically on the butterfly valve of the throttle body. The throttle position sensor (TPS) reports to the computer the position of the throttle butterfly valve, which the ECM uses to calculate the load upon the engine. The fuel system consists of a fuel pump (typically mounted in-tank), a fuel pressure regulator, fuel lines (composed of either high strength plastic, metal, or reinforced rubber), a fuel rail that the injectors connect to, and the fuel injectors. There is a coolant temperature sensor (ECT) that reports the engine temperature to the ECM, which the engine uses to calculate the proper fuel ratio required. In sequential fuel injection systems there is a camshaft position sensor (CKP), which the ECM uses to determine which fuel injector to fire. The last component is the oxygen sensor. After the vehicle has warmed up, it uses the signal from the oxygen sensor to perform fine tuning of the fuel trim. Based on a ‘programmed’ interpretation of all this input data, the ECU gives the various ‘commands’ to the Engine’s fuel intake and spark ignition timing systems, to deliver an overall satisfactory performance of the Engine from start to shut down, including ‘emission control’. A multipoint fuel injection system generally delivers a more accurate and equal mass of fuel to each cylinder than can a carburetor, thus improving the cylinder-to-cylinder distribution. Exhaust emissions are cleaner because the more precise and accurate fuel metering reduces the concentration of toxic combustion byproducts leaving the engine, and because exhaust cleanup devices such as the catalytic converter can be optimized to operate more efficiently since the exhaust is of consistent and predictable composition.