# PlugIn "Fuel consumption" PlugIn "Fuel consumption" calculates and displays the ratio of fuel in percentage of maximum possible for the diagnosed engine. PlugIn "Fuel consumption". In order to perform this test, oscilloscope probe must be connected in parallel with operating lead of an electromagnetic petrol injector and must be connected with 5-th analog input of USB Autoscope III. Then for start PlugIn choose "Control => Load user preset => Consumption"
Principle of measurement. In the additional equipment lists for the instrument panel of the car, it is possible to see the onboard computers, capable to trace and display the fuel consumption. Calculation of the fuel consumption value is carried out on the basis by a injectors operated signal at known value of productivity of installed on the engine injectors. Measurement of the fuel consumption value looks as follows. At designing of a control system for each engine model choose injectors with necessary productivity. On the one hand, productivity of injectors should be sufficient for submission of necessary quantity of fuel on the maximal loadings and the maximal RPM. On the other hand, productivity of injectors needs to be chosen minimally possible for maintenance of high accuracy of a dosage of fuel on modes with minimal loadings and at idle. Hence, at designing of the control system of the engine, choose the minimal productivity of injectors at which submission of necessary quantity of fuel on the maximal loadings is provided. When the engine works at the maximal loading and maximal RPM, the actual fuel consumption is a maximal possible for this engine and it can be accepted for 100%. At work in such mode, by the voltage waveform of the injectors control signal is possible to see, that fuel injectors appear constantly open. When the engine works at idle, the actual fuel consumption is minimal, and for the majority of modern engines consists ~2% from maximal. The fuel consumption measured in percentage of maximum possible for this engine can be called "the relative fuel consumption". Calculation of value of the relative fuel consumption is carried out by a injectors operated signal by multiplication of the injectors opening duration to frequency of its operation. At doing the diagnostics of the engine measurement of the fuel consumption value make at temperature of the engine above 80°C. Value of the relative fuel consumption when engine at idle without loading can be increased on three principal causes: the increased loading on the engine, low productivity of the fuel submission system or malfunction of the engine control system. Loading on the engine can increase because of the connecting of the external load (power steering, the air conditioner, consumers of the electric power…) or because of the increased intrinsic losses because of deterioration of the engine mechanics. Productivity of the fuel submission system can decrease due to pollution of the fuel injectors, or due to pressure decrease in fuel rail because of deterioration of the fuel pump, pollution of the fuel filter or a reception grid, or because of malfunction of a fuel pressure regulator. In case of occurrence of malfunction of the engine control system of causing infringements of the air/fuel mixture ratio (malfunction of the Oxygen-sensor, the coolant temperature sensor, air flow sensor, the throttle position sensor… or their circuits), efficiency of combustion of such mixture decreases. In that case, for example, for ensuring of the set RPM at idle, a lot of a mixture is necessary already. For this reason the engine control system opens the idle actuator and accordingly increases quantity of submitted fuel that leads to increase of the relative fuel consumption value.