Jerk limit - dip - a perceptible delay in engine response to pressing the accelerator pedal (gas).
Conventionally, three types of car jerks can be distinguished:
- at the time of the start of the movement of the car;
- when accelerating the car;
- with the steady movement of the car, i.e. at a constant position of the accelerator pedal (gas).
To determine the causes of jerks when driving a car with an injection engine, special diagnostic equipment is required, therefore, in this case, we recommend contacting a car service that specializes in repairing fuel injection systems. However, as practice shows, in most cases jerks are caused by insufficient fuel pressure in the fuel line (ramp) engine or throttle position sensor malfunction.
With some skills, the cause of jerks can be determined independently.
Jerk at the moment of the beginning of the movement
At the moment of the beginning of the movement of the car most often there is an extreme case of a jerk - a failure. The most unpleasant sensations are associated precisely with the delay in the response of the engine to pressing the pedal «gas». Sometimes the engine on the car even stalls.
A jerk occurs at the moment the throttle valve opens, when, according to the signal from the throttle position sensor, the electronic control unit determines the moment of transition from idle to load mode and must increase the amount of fuel supplied through the nozzles. In case of insufficient pressure in the fuel line (even with increased injection duration) there is not enough fuel for a smooth starting of the car. For the procedure for checking fuel pressure, see subsection «Checking the fuel pressure in the engine power system».
Jerks when accelerating the car
The cause of jerks during acceleration of the car may be, as in the previous case, insufficient fuel pressure in the fuel line. The electronic engine control unit, having received a signal from the throttle position sensor about the intensive opening of the damper at a large angle, seeks to maximize the fuel supply, but due to the reduced fuel pressure it is not able to do this. The reasons for this phenomenon and the method of verification, see above «Jerk at the moment of the beginning of the movement».
Jerks in steady motion
Such jerks are most often caused by a malfunction of the ignition system. Diagnosis and repair needed (see sect. 9 «electrical equipment»). On the way, you can try to do the following yourself:
- carefully inspect the underhood space. Switch off the ignition and check the reliability of fastening and landing of all wires and connectors at the ignition coil and high-voltage wires. Start the engine and listen to its work: crackling during breakdown of high voltage «to ground» weak but distinct. In complete darkness, a spark is clearly visible during breakdown;
- replace spark plugs regardless of their condition and mileage. Pay attention to the condition of the spark plugs: if they are not up to standard, it may be necessary to repair the engine or its systems.
A specific cause of jerks during the steady movement of a car with an injection engine may be a failure of the throttle position sensor (TPS). Additional symptoms confirming a malfunction of the TPS sensor:
- uneven engine idling;
- reduction in maximum engine power.
The throttle position sensor is non-separable and therefore non-repairable. If a Throttle Position Sensor is Faulty (see «TPS (throttle position sensor)»), replace the sensor assembly.