A jerk at the start of movement (VAZ-2115)

At the moment of starting the movement, the extreme case of jerking - failure - often occurs. The most unpleasant sensations are associated with the delay in the engine's response to pressing the gas pedal.

Sometimes the engine even deafens. The jerk occurs at the moment the throttle valve begins to open, when the ECU determines the moment of transition from idle mode to load mode based on the signal from the throttle position sensor and must increase the amount of fuel supplied through the injectors. If the pressure in the fuel line is insufficient, even with an increase in the injection duration, there is not enough fuel for smooth starting.



To check the fuel pressure, connect a pressure gauge with a measurement limit of 10 kgf/cm² to a special fitting on the fuel line using a section of a suitable hose. When the engine is running, the pressure in the fuel line should be at least 3 kgf/cm².

Note: The design of the pressure test nipple is similar to that of a tire valve with a valve core. Therefore, the hose tip of a foot tire pump can be used to connect the pressure gauge hose.

The reasons for the decrease in pressure may be:

• faulty fuel pressure regulator. In addition, regulator failure may be caused by a loose hose fit on the regulator vacuum chamber fitting;

• clogged fuel filter;

• faulty fuel pump.

Note: Methods of checking and pressure regulator replacement, fuel filter and the fuel pump, see the "Engine" section in the "Fuel system" subsection.