What is That Popping Sound Under the Hood?

engine injection
There should be no popping sounds coming from your engine. Getty

There are all kinds of sounds that cars make. Most of them are completely normal and acceptable signs of a well-tuned machine. Low rumbles from the tail pipe, a soft rhythmic hum from the engine compartment, even a slight thunk sound when you first turn on your air conditioner - these are all good news. There are also lots of sounds that you never want to hear coming from under the hood. One of these not so welcome noises is a popping sound.

 

A popping sound coming from your engine can be bad news. If you suddenly hear a loud pop or bang in the engine area, pull over to the side of the road and check it out. Be on the lookout for smoke or fire, two things you should never see under the hood. Occasionally, especially in older vehicles, an engine backfire can actually reverberate through the air intake and blow a hole in your plastic air box. This is rare, but it’s something to look for if you hear a small explosion under the hood. 

Most of the time, the popping sounds you hear will be far less explosive. Here are some examples of popping that may indicate a problem that you can deal with. 

Popping, coughing and hesitation on acceleration. If your engine complains every time you step firmly on the gas pedal, this is an engine performance issue. For example, consider leaving a stoplight. If you press the accelerator and, instead of taking off, your engine gives you some stutters and pops, you should:

1. Check for engine codes that may indicate the problem
1. Run a good quality fuel injection cleaner
2. Check your spark plugs
3. Inspect your spark plug wires
4. Test your engine compression

If the popping sound is more rhythmic and occurs more frequently as you rev the engine, you may want to look for an exhaust leak.

The exhaust manifold is on the side (or sides) of your engine toward the bottom. A blown exhaust gasket can cause some pretty loud sounds from that area, but it will always be louder and faster as you rev the engine higher. IN some cases you may hear an exhaust leak like this when you first start the engine, but as it warms up it seems to magically seal itself! This is because the expansion of your exhaust manifolds’ metal can actually seal a small leak. Any exhaust leak should be taken care of as soon aspkossible. The possibility of carbon monoxide gas leaking into the passenger compartment can be deadly in the wrong conditions, so don’t stall on this repair. 

Another pop-like sound that can come from the engine area involves your belts. If a belt is worn or frayed, often a piece of the belt will peel away but remain attached to the belt. This turns into a large, flapping noisemaker as it rotates through the pulleys and slaps against mounts, water pumps, alternators or whatever is in the way. This will make a rhythmic slapping or popping sound very different from an exhaust leak. A bad belt needs to be replaced as soon as possible or it is likely to leave you stranded someplace. 

Popping sounds can be hard to pinpoint.

Before you convince yourself that your engine is going pop-pop-pop, be sure the noise isn't actually a clunk or knock coming from your suspension or steering. There are different problems, no less serious but different in terms of diagnosis.