What Does It Mean When an Engine "Knocks"?

A combustion engine is supposed to run smoothly from start-up to shut-down. Occasionally an engine will produce noises that are difficult to diagnose. Sometimes, when you hear a strange sound coming from under your hood, you may not know what to do. A "knocking" sound is the most typical engine noise indicating a mechanical problem that can be fixed if diagnosed correctly and early.

Noted below are a few facts about why an engine knocks and what can be done to resolve these issues.

What is Engine Knocking?

Knocking in your engine, also described as pinging, can mean one of several problems. Some may be easily fixed while others may indicate major damage. The knocking sound often occurs when the air-fuel mixture is incorrect, which causes the fuel to burn in uneven pockets rather than uniform bursts. Left untreated, it can cause damage to the piston and cylinder wall. A knocking sound can also be caused by a lack of lubrication in the upper cylinder head area. This is typically a ticking sound created by valves and lifters that are loose or not receiving enough oil.

In general, the most common cause of engine knocking is related to the engine's ability to operate efficiently. Noted below are a 3 of the common causes of ignition-system and fuel-related engine knocking.

1. Fuel Has a Low Octane Rating

If you put in fuel with an octane rating too low for your vehicle, it can create a knock. An octane rating is the measure of a fuel type’s ability to resist premature detonation of the air-fuel mixture in the engine. The combustion causes the “knocking” or “pinging” sound you hear.

To prevent this from happening, use gasoline with an octane fuel rating at or above what the manufacturer recommends. An octane booster, which can be bought at an auto parts store, can help restore the correct octane rating and stop the knocking.

2. Carbon Deposits Restrict the Efficient Burning of Fuel

Fuels for vehicles are required to have a carbon cleaning detergent, but they may not prevent carbon deposits from forming. As fuel mixes with oxygen, it is burned. Since gasoline and diesel are made up of multiple carbon molecules, the residual of carbon will form on valves, spark plugs, and other components involved in the combustion process. This reduces the amount of volume inside the cylinder and increases the amount of compression.

In most cases, using a special fuel injector cleaner or additive designed to clean carbon deposits on engine components can resolve this issue.

3. Incorrect Spark Plugs or Wrong Spark Plug Gap

If any spark plugs other than what is recommended by the manufacturer is used, it can cause the knocking sound you hear. The spark plug has a certain heat range, which means it withdraws heat from the combustion chamber. Using the wrong part can prevent it from working correctly. It's also common for engine knocking to occur when the spark plug gap is not correctly set.

The spark plug gap is the place where the spark plug ignites the air-fuel mixture that helps power the car. Too narrow of a gap creates a spark too weak to perform this task, and too wide a gap might stop a spark from firing at all, or to only misfire rapidly.

Resolving these types of engine knocking problems is usually rather simple and something most car owners can do themselves. In other instances, it might be prudent to contact a professional technician to correctly diagnose the source of the knocking and recommend the right repairs.


Next Step

Schedule Noise from engine or exhaust Inspection

The most popular service booked by readers of this article is Noise from engine or exhaust Inspection. Once the problem has been diagnosed, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. YourMechanic’s technicians bring the dealership to you by performing this job at your home or office 7-days a week between 7AM-9PM. We currently cover over 2,000 cities and have 100k+ 5-star reviews... LEARN MORE

SEE PRICING & SCHEDULING

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Recent Noise from engine or exhaust Inspection reviews

Excellent Rating

(324)

Rating Summary
297
10
3
1
13
297
10
3
1
13

Claud

8 years of experience
303 reviews
Claud
8 years of experience
Cadillac STS - Noise from engine or exhaust - Oak Park, Michigan
Claude is very polite and courteous! He has exceptional knowledge and is very professional! Claude is welcome to working on my automobile every time I request Your Mechanic for my auto needs.

Andrew

11 years of experience
696 reviews
Andrew
11 years of experience
BMW 740i - Noise from engine or exhaust - Shawnee Mission, Kansas
i thought it was an Adjusting pulley. Andrew looked and said that the fan blades were no aligned with the the Fan Housing. We then listened and I told him it could be the impeller in the water pump but the sound wasn't "metallic". He said that the impellers in my water pump were a plastic composite. He was right on both accounts. What a PRO! I recommend this guy to anyone. He was on-time, courteous and RIGHT in the diagnosis. I'll ask for him again.......next time something else breaks.

Michael

21 years of experience
139 reviews
Michael
21 years of experience
Dodge Dart - Noise from engine or exhaust - Pomona, California
Very thorough and honest. Explained everything to my daughter and took pics for us of what the PEP Boys mechanic did wrong. Will definitely be calling Michael again. So very glad I took a chance with Your Mechanic. They will definitely be my go to people from now on.

Mike

13 years of experience
139 reviews
Mike
13 years of experience
Buick Rendezvous - Noise from engine or exhaust - Raleigh, North Carolina
Mike was awesome!! Professional, knowledgeable and complete. Took time to explain what the issue is. I look forward to him working on my car again when needed. Thanks

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

Related articles

How a Modern Engine Works
You You turn your key in the ignition, and the engine fires up. You press the gas and the car moves forward. You take the key out and the engine turns off. That’s how your engine works, right? It's a...
What Are the Best Spark Plugs for Normal Use?
Spark Spark plugs are essential components of your ignition system. They’re responsible for supplying the spark that ignites fuel and starts the combustion process. However, not all spark plugs are created equal. You’ll find “normal” plugs on the market, but...
How a Car Ignition System Works
The The complicated process of a vehicle's ignition system requires precise timing on the part of the various systems involved. Starting a vehicle involves much more than just turning a key in the ignition switch; it requires each system to...

Related questions

Loses power 60 mph

Hi! I believe your problems are unrelated and not caused by one another. I think it's more so awkward timing that both present problems than anything else. You may be in need of a tune-up. I suggest that you have...

Engine shutdown caused by worn out key

Hello. Unfortunately, there is no other way to get these unless you find a BMW certified repair shop. Due to the security concerns with these vehicles it takes a special computer to be able to program new keys to it....

Spark knocking in car

Your neighbor is correct, your particular model does not have an EGR valve. I suggest that you have a technician check the condition of the spark plugs and test the spark plug wires. Either of those of those components are...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com