what causes tachometer to fluctuate

• 2022-01-05

The reasons for the tachometer to fluctuate are as follows:

1. The charging line is faulty

The failure of the charging line may be caused by generator failure, battery voltage sensor failure, loose battery pile head, etc.
Because the generator needs to charge the battery when the vehicle is running. When the battery is not charged or not charged enough, the engine ECU will increase the engine speed so that the generator can charge the battery, which causes the tachometer to go up and down during driving.

2. The throttle valve is faulty

The fault of the throttle may be the fault of the throttle position sensor or the fault of the throttle control motor. As the name suggests, the throttle position sensor detects the opening of the throttle valve to control the fuel injection quantity; The function of the throttle control motor is to open the throttle an angle according to the depth of the throttle.

When these two components fail, the air intake of the engine will change, resulting in the tachometer up and down during driving.

3. PCV valve or canister solenoid valve failure

PCV valve, that is, the positive crankcase ventilation valve, is used to make the combustible mixture flowing into the cylinder return to the intake pipe again and inhale into the cylinder for combustion; The function of the carbon canister solenoid valve is to send the gasoline vapor in the fuel tank to the intake pipe and suck it into the cylinder for combustion, so as to reduce fuel consumption.

When these two valve bodies fail, the fuel burned in the cylinder will deviate from the setting of ECU, resulting in the tachometer up and down during driving.

4. Engine carbon deposition

Carbon deposition in engine throttle and combustion chamber will seriously affect the combustion of mixture. Carbon deposition in throttle valve will affect engine intake; Carbon deposition in the combustion chamber will affect fuel injection and ignition, and seriously cause early combustion and deflagration. This will cause the engine speed to fluctuate.

The solutions of tachometer to fluctuate below:

1. Clean the fuel injection nozzle and intake manifold;

2. Check and clean the carbon deposit inside the throttle valve and combustion chamber; Because during cold start, the carbon deposit will adsorb a certain mixture, which will lead to too thin mixture and poor mixture atomization during start-up, resulting in uneven combustion state of the engine;

3. The carbon canister or carbon canister solenoid valve has problems, resulting in too rich mixture during startup, which will also make it difficult to start;

4. Check the working condition of spark plug;

5. Due to the failure of clutch switch or other sensors, because the engine is controlled by ECU, the computer will continuously collect the signals of various sensors and control the fuel injection amount of the engine during gear shift, refueling and oil collection.

Once there is a problem, the computer program will be disordered and the rotating speed will be unstable.