Sensors and ECU Overview

Fuel Injection
An optimal fuel injection has everything to do with the relationship between the amount of oxygen and fuel. If there is a shortage of oxygen, not all fuel burns, resulting in a loss of power, but if there is an excess of oxygen, there is also a loss of power. The optimum combustion ratio for a complete combustion is between 14.7 to 1: one gram of petrol requires 14.7 grams of air. Unfortunately, this ratio is not suitable for every situation. The most power you have at a ratio of 12.5 to 1 and the most economical you drive with a ratio of 15 to 1. It is therefore up to the ECU to estimate which ratio is best for each situation at a given moment. The MEMS ECU has a hard-wired map that it uses to determine the correct ratio depending upon the load on the engine.

The Manifold Absolute Pressure Sensor (MAP sensor) is used in the electronic system of an internal combustion engine. The MAP sensor provides information about the pressure in the intake manifold. This information is used to calculate the air density and the air mass ratio.

Coolant temperature sensor What the coolant temperature sensor does, of course, speaks for itself. This sensor can also supply data for, for example, the electric fans or the coolant temperature on the instrument panel.

The Lambda Sensor is a sensor also known as the oxygen sensor (O2 sensor). This sensor measures the amount of oxygen in the exhaust gases. If there is too much oxygen then the ECU add more fuel to the mixture making the mixture rich. If too little oxygen then the ECU reduces the fuel making the mixture lean. The ECU tries to balance the air : fuel ratio using the ECU mapping table and the O2 sensor.

The Crankshaft Position Sensor is used to ‘synchronise’ the engine at start-up, so that the ECU knows when to inject the fuel. The crankshaft position sensor is often used as a source to measure the engine speed. So you can imagine that a problem with this sensor has a direct effect on the overall operation of the fuel injection system.

The Throttle Position Sensor is used to determine the position of the accelerator pedal. When the accelerator pedal is pressed deeper, the amount of air and fuel sent to the engine will of course also increase.

Air Fuel Ratio Map