Why does the car shake when starting?

These problems with car vibrations when starting are not uncommon. The car could shake when it is turned on mostly because of engine and fuel problems, but there are also some other causes that could make the car shake when you start it.

A common situation is when vibration occurs when the cold engine is started. However, after warming up the motor at the time of subsequent starts, vibrations may not be observed. These signs and symptoms usually indicate problems that need to be checked.

Vibrations can be either constant, regardless of heating and loads on the unit, or manifest itself in a certain operating mode (idle or high speed, cold or hot). The engine vibration can also manifest on a cold internal combustion engine, however, as it warms up, it completely disappears.

This is one of those annoying problems that starts out quietly and gradually, and subtle enough that you won’t notice or ignore them. One thing is certain, do not underestimate this problem and know the root causes of the car’s vibration before they can cause serious damage.

Why do cars shake when starting? Possible reasons

If, when starting a car, you will notice vibrations, then these can happen due to the following reasons:

1. Low fuel in the tank

No matter how trite it may sound, you always need to check the level of the fuel in the tank, perhaps the reason is this simple issue.

2. Using low-quality fuel

There are lots of gas stations that have low-quality fuel, which, in addition to fuel, can contain a large amount of water. To make sure your fuel is free of water, pour 1 to 2 liters into a bottle and leave it for a few hours. If there is water, it will sink to the bottom being easy to notice.

If you own a car with a diesel engine, and the engine stalls immediately after starting at a freezing temperature, then perhaps the reason lies in the frozen fuel. As you know, diesel can freeze in severe frost.

3. A discharged car battery

Each vehicle uses a variety of devices and equipment that require charging. Even when the motor is not running, and all energy consumers are turned off, some devices may consume a minimum charge. 

For example, the reason for inoperability can be an ignition relay or a fuel pump, these elements often cannot work with an incompletely discharged battery. You should also pay attention to checking the starter if the start of the internal combustion engine itself has become more difficult.

4. A bad fuel pump

The fuel pump is most often the cause why engines start up and immediately stall. Its incorrect operation, failure, as well as clogging of the fuel filter can lead to incorrect engine operation. If the fuel filter is clogged, then it simply will not be able to optimally pass the fuel through itself, or it will pass it, but too slowly. 

In this case, fuel will enter the cylinders, but after the engine is started, the fuel quantity will be insufficient to ensure the optimal operation of the engine. Thus, a few seconds after starting, the car will shake and it may stall. Think about the last time you changed the fuel filter. This element needs to be replaced periodically.

5. Bad spark plugs

The spark plugs are crucial for the ignition system as a whole. Like any other parts, spark plugs wear out over time and when their service life comes to an end, they begin to work intermittently. 

In addition, the reason may lie not in wear, but in the formation of carbon deposits that can be black or white, which may be due to various factors. Carbon deposits often appear because the air-fuel mixture is formed incorrectly, or due to low-quality fuel.

7. Faulty spark plug wires

High voltage wires that connect the spark plugs to the ignition distributor or coil can wear out over time, which can damage the insulation on them. If the insulation is weak, then humidity can cause a voltage short circuit causing an improper engine operation that can be manifested through vibrations.

8. Worn-out timing belt or timing chain.

As a result of long-term use, because there is no longer a correct adjustment of the chain or belt, it will begin to wear out. This fault may appear not even with a worn-out belt or chain, but when the engine is started in severe frost.

9. Problems with ECU

Often, malfunctions of this kind are associated with errors in the operation of the electronic control unit and related systems. Moreover, it should be borne in mind that such malfunctions cannot always be reported by light indicators on the dashboard. This will require deep checks at a good car repair shop.

10. A bad oxygen sensor

One of the most unpleasant problems is poor compression in the motor’s cylinders. It may be because the service life of the internal combustion engine is coming to an end and it may soon be necessary to do a major overhaul.

11. Engine mounts

Bad engine mounts are a common cause why the car shakes. This problem is present when the car is starting but it can be felt better when the car is idling.

In this case, the cold engine vibrates most strongly when the temperature in the engine compartment has not yet risen. Often, with warming up, the rubber in the structure of the supports softens causing the vibration intensity to decrease. For an accurate determination, you need to check the engine mounts.

12. Bad injectors

Dirty or failing injectors, especially on a diesel engine, can also cause the cold engine to vibrate when turning on.

13. Faulty idle speed sensor

Problems with idle speed or actuators often cause RPM to float on a cold engine. During spikes in speed, the crankshaft speed can drop to low values ​​that will cause the engine to almost stall. When this happens, you will feel strong vibrations.

Other reasons why car vibrates when starting

Has your car’s engine been repaired recently?

If the engine was recently disassembled for repair, possibly overhaul, then there is a high probability that the crankshaft was not properly balanced after mounting. The result is increased vibration.

We also can note that after repairing the engine, different weights, which the parts of the cylinder-piston group have, can lead to imbalance and vibrations. The greater the difference in weight, the stronger the vibration will be.

Vale burnout leads to a decrease in compression. As a result, the fuel is not compressed properly, and the cylinder does not work, the mixture does not ignite, or the charge ignites intermittently. 

In any case, the engine is working at a reduced capacity, causing strong vibrations to go through the body when starting. With warming up, the compression can increase, after which the vibrations decrease or completely disappear until the next cold start.

I also want to add that many car owners are faced with increased vibrations after an incorrect installation and tuning of LPG (for example, when the system immediately supplies gas to a cold engine without starting the engine on gasoline).

Finally, we note that the cause of increased vibrations in some cases may be caused by transmission problems.

Conclusion

As you can see there are a lot of reasons why your car shakes when starting, in order to determine the cause of vibrations, it is recommended to carry out a full comprehensive diagnosis of not only the engine but the other listed parts. Start by checking engine mounts first because these parts are often responsible for car vibrations.

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