Engine Knock Case Study

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Engage the ignition and your car should immediately respond with a familiar noise, ranging from a muted hum to a raucous bellow, depending on what’s under the hood. Beyond the expected sounds, a few others may intrude, serving as a warning that a breakdown may be imminent. Here’s how to interpret that knocking noise and other mysterious sounds.

1. Engine Knocking or Pinging

The wrong kind of fuel, specifically gasoline with too low of an octane rating can cause an engine to knock or ping. Modern cars have knock sensors, which mitigate the problem, but this part may need to replacement if the sensor has failed.

If you suspect the problem is low octane, you can add octane booster to eliminate the problem. Other causes of engine knock could
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Under the Hood Squealing

If you hear loud squealing coming from underneath the hood, you better hope that the neighbor’s cat wasn’t looking for a warm place to rest. Once you have determined the noise has nothing to do with a feline percussion, the problem likely has something to do with a belt.

Specifically, the alternator belt —usually called a serpentine belt may be slipping. This belt controls several parts in proximity to the engine, including the alternator, water pump, steering pump, air pump and the air conditioner compressor. When it slips or becomes worn, it can create quite a racket. This noise serves notice to address the problem at once or risk becoming stranded.

3. Squeaking or Grinding Brakes

Apply the brakes and your car should come to a safe halt. However, if the brakes squeak or squeal when applying the brake pedal, then one or more problems may be the
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For everyone else, a roaring engine under acceleration is not the norm. Likely, an exhaust system problem is making itself known.

For instance, the exhaust system may have developed a hole due to rust. Replacing the worn part should resolve the problem. On the other hand, if the exhaust system is fine, the roaring may have something to do with the transmission. In cars equipped with an automatic, the transmission may not be shifting to the next gear. For vehicles with a manual transmission, the clutch may be slipping. Problems with an automatic transmission can become quite expensive, especially if ignored.

5. Clunk, Bang or Pop

Much like your favorite breakfast cereal, your car may make an assortment of noises, including various clunks, bangs or pops. Unlike your cereal, isolating the noise can be a challenge!

One possible reason for clunking or banging may point to a problem with the suspension system, specifically worn shock absorbers, strut mounts or ball joints. In each case, vehicle control is at risk, so you will need to fix the problem at once. If you hear a popping sound while driving at low speeds and when making sharp turns, a worn rear differential may be the cause.

6. Under the Hood Hissing or

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