The engine rattles when idling. Whose sound is it?

There are many reasons why a car engine makes a 'da da' sound. Some are normal, and some may be malfunctioning. Generally, there may be several situations for making a 'da da' sound:

1. Valve sound

Engine When working, the intake and exhaust valves should be opened and closed continuously. In the early engine, the valve rocker arm was driven by the camshaft, and the rocker arm opened the valve again. However, with this structure, the rocker arm and the valve cannot be in direct contact, and a little gap should be left, otherwise the metal thermal expansion after the engine temperature rises may cause the valve to not close tightly.

But that structure requires regular valve clearance adjustment, which is very troublesome. Therefore, people invented a new structure. A metal cap was placed on the valve stem, and the inside was connected to the lubricating oil passage, and the pressure of the lubricating oil was used to automatically adjust the valve clearance.

When the engine is cold, the oil pressure is not fully established when the engine is started, so the valve clearance may be relatively large, and there will be more obvious ' 'Da Da' sound, this sound disappears when the oil pressure stabilizes.

2. The sound of the timing chain tapping the tension plate

To be precise, the sound is more like ' 'Papa Papa' or 'Blala La'. Because the timing chain is relatively long, the chain may jump and cause tooth jump when the engine is running at high speed. Therefore, the timing chain is designed with a tensioner. The oil pressure pushes the tensioner, and the tensioner then pushes the tensioner plate to top the chain. Tighten it, let it run stably, and avoid jumping.

The tensioner is loose when the cold start oil pressure is not fully established. At this time, the timing chain beats the tensioner plate There will be a 'clap' or 'pop' sound. However, this sound lasts for a short time and will disappear within a few seconds because the oil pressure builds up quickly.

3. Injector noise

This is basically the biggest noise when the engine is running, idling When you open the engine compartment, you can hear the 'Da Da' sound from the fuel injector in all likelihood. Because the inside of the fuel injector is a solenoid valve, the solenoid valve opens when the ECU supplies power to the fuel injector. When the power is off, the solenoid valve closes quickly under the action of the spring force, which will make a relatively obvious noise.

4. Carbon canister solenoid valve

The carbon canister solenoid valve is controlled by the ECU through the duty cycle. That is to say, it will constantly turn on and off when it is working, and control the flow through the switching frequency, so it will also make a 'click' sound when it is working. However, the oil and gas in the carbon canister does not participate in the combustion at idling speed, so the solenoid valve of the canister does not work at this time.

Failure sound

There are many reasons for this failure. The slightest one may be the aging part of the belt rupture. The broken belt whipped other parts to make noise. More serious may be that the engine pulls the cylinder causing the piston skirt to hit the cylinder wall.

How to judge whether it is a normal sound or a faulty sound

An experienced master can judge that it is inseparable by listening to it, so when you suspect that the engine has an abnormal 'da da' The safest way to find a reliable repair shop is to check it.

Of course, you can also judge by some small tricks. Normal 'click' sounds are basically solenoid valve parts This kind of sound is relatively crisp and has a 'rustling' feeling, while the fault sound is generally dull or strong, and it obviously feels abnormal when it is heard. In addition, when you step on the accelerator to increase the speed, the sound of the normal solenoid valve will not increase significantly, but the frequency will increase. Not only will the frequency of the fault sound increase, but the sound will also become louder.

It can also be judged by the frequency of the sound. For a common four-cylinder engine, the engine will spray every revolution. Fuel oil twice, if the idling speed is 750 rpm, then the fuel injector will work about 25 times per second at idling speed, so the sound of the fuel injector you hear is very high frequency. Some fault sounds have a low frequency, such as the noise from a broken belt. Because the belt is very long, the engine rotates several times before the belt rotates once, so the frequency of the beating sound is very low.

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