What Causes Engine Knock - Subaru Service Questions in Salt Lake City, UT

For ideal performance, the right mixture of air and fuel are blended in the right ratio and detonated at the right time in each of your engine's cylinders -- and it happens thousands of times a minute. That's why modern engines are precisely tuned, computer-controlled machines. The slightest imperfection in this process can result in problems. One such problem is engine knock. It's an audible knocking or pinging sound coming from your engine as you drive, and it means some of the fuel is detonating too early inside the engine. This can rob you of performance and cause additional wear on the engine over time. Learn how to keep this from happening on your car, and what might need to be done to fix it below.

Engine Cutaway Illustration

4. Insufficient Octane Level In Fuel

Most Subaru engines run on regular unleaded gasoline -- but the powerful Subaru WRX STI rally sports car requires premium fuel with a higher octane rating. Why exactly is that? It has to do with engine knock.

The higher the octane rating, the greater the fuel's resistance to combustion. In more powerful, higher-compression engines, regular fuels will begin to partially combust too early. These tiny explosions inside the engine will be heard in the cabin as a repetitive pinging, clicking or knocking noise. Using a premium fuel with a higher octane rating can help. Higher octane fuels are less prone to early detonation -- they'll remain unburned until the spark plug detonates the whole mixture in a controlled explosion that delivers the best possible power and fuel economy.

Spark Plugs

3. Incorrect Ignition Timing

If the fuel inside the cylinders isn't detonating at the right moment in the piston's travel, this can also cause knocking. On older cars with spark distributors and individual spark plug wires, this could be caused by engine timing that's incorrectly adjusted. On modern cars, the ignition timing is usually computer-controlled. A problem with ignition timing on a newer vehicle is therefore much less likely, however it's not impossible. You might have a bad sensor sending incorrect feedback to the engine's computer, or the computer itself may need to be replaced or recalibrated.

2. Imperfect Air/Fuel Ratio

Every engine is designed with a specific air/fuel ratio in mind for optimal performance. When this ratio is achieved, you get the most horsepower using the least amount of fuel. Over time, systems can degrade and parts can break down that cause the air/fuel ratio in the engine to come out of whack. For example, something as simple as a clogged engine intake filter can choke the engine, leading to a lean air/fuel mixture and engine knock since the resulting mixture burns more slowly than intended. Or, you might have a leaking fuel injector adding excess fuel to the engine and leading to a rich air/fuel mixture. In either case, you might find your car is sluggish to drive and suddenly consumes fuel much more quickly! To get this fixed, you may want an in-depth diagnostic from one of our talented dealership professionals.

Engine Valvetrain

1. A Different Kind Of Engine Knock: Rod Knock & Lifter Knock

Over time, the bearings that keep engine parts moving smoothly against one another can wear out. Bad bearings can introduce a little bit of clearance, allowing piston connecting rods, valve lifters and other parts to rattle loudly as you drive. This is called rod knock or lifter tick, and it can be hard to tell what's going on under the hood just from the sound if you're not used to working on different cars all day. No matter what the cause of the knocking sound coming from your engine, these parts should be fixed right away, as more damage could be done to adjacent components if the issue is left unaddressed.

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  1. Nate Wade Subaru

    1207 South Main
    Salt Lake City, UT 84111
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    • Sales: (888) 586-8323

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Nate Wade Subaru

1207 South Main St
Directions Salt Lake City, UT 84111

  • Sales: (801) 658-9379
  • Service: (801) 328-1327
  • Parts: (801) 328-0061