Engine Misfire vs Engine Knock: How to Identify Different Performance Problems and Their Repair Costs

When your vehicle starts making unusual sounds or running roughly, it’s crucial to understand whether you’re dealing with an engine misfire or engine knock. While both issues can cause poor performance and potential damage, they have distinct causes, symptoms, and repair costs that every car owner should understand.

Understanding Engine Misfires

An engine misfire occurs when one or more cylinders fail to complete all of the combustion steps properly. When an engine misfires it’s because there’s an incorrectly timed spark or lack of spark from the spark plug in the combustion cycle, and could indicate a number of issues such as a bad spark plug, an overly lean or rich fuel mixture, slipping timing belt, or an air or fuel leak from the engine.

Common symptoms of engine misfires include:

• A palpable loss of power resulting from a vehicle that may be running on fewer cylinders than normal, or a brief hesitation in the delivery of power when gas is applied. You may also feel intermittent jerking, bucking, or stumbling from the engine
• A loud backfiring noise
• Rough and/or slow acceleration
• Check engine light activation

Understanding Engine Knock

Engine knock or engine detonation occurs before the spark plug ignites the air-fuel mixture in the engine’s cylinder. When the pressure or temperature in the cylinder’s combustion chamber is too high, pockets of fuel and air may combust before the spark plug fires.

Engine knock (also called detonation knock) happens when the air-fuel mixture in the engine doesn’t burn properly or when metal parts inside the engine collide when they shouldn’t. It isn’t always a loud knocking noise and can sometimes sound like a metallic ping, repeated tapping, or clinking of metal parts.

The key difference is that engine knock/pinging is when fuel combusts unevenly in the cylinder, creating a knocking sound, this is often confused with a misfire. However, a knock happens when the cylinder fires, while a misfire is a failure to fire correctly.

Causes and Risk Factors

Engine misfires can be caused by several factors including worn spark plugs, faulty ignition coils, fuel delivery problems, or timing issues. A lean air-fuel mixture – basically an air-heavy mixture, so either you are getting too much air or too little fuel in your combustion chamber – can also cause problems. Fuel has a cooling effect on combustion temperatures, so when too little fuel is being delivered to the engine, combustion temperatures can go up.

Engine knock is often related to fuel quality issues, carbon buildup, or improper ignition timing. Engine knock creates extreme pressure in the cylinder that can damage internal engine components like the pistons, bearings, connecting rods, or the cylinder wall. It also raises the temperature in the cylinder dramatically, which could lead to more instances of pre-ignition.

Repair Costs: What to Expect

Engine Misfire Repair Costs:

Fixing an engine misfire can cost less than $100 or nearly $2,000, depending on what’s causing the issue and how difficult the repair is on your vehicle. Depending on the cause of the misfire, the repair and replacement costs might range between $100 and $1,000.

Specific repair costs include:

• Replacing spark plugs will likely cost somewhere between $80 and $320 if you have it done professionally
• Replacing your timing belt usually costs somewhere between $300 and $500. If your vehicle has a timing chain, it may cost as much as $2,000 to replace
• The most frequent causes of a cylinder misfire are the ignition coil, injector, or spark plug. I would anticipate the repair cost to be between $200 and $400, depending on the issue

Engine Knock Repair Costs:

Engine knock repairs tend to be more expensive due to the potential for internal engine damage. If you’re looking for “how much does it cost to fix engine knocking?” Expect to pay somewhere between $500 and $1000.

For more severe cases involving rod knock:

• On average, expect to spend between $2,000-$3,000 for both parts and labor. Usually, the job consists of replacing the seals, gaskets, connecting rod bearings, cylinder head bolts, and flushing out the engine and cooler lines
• The last thing you want is to find out your engine needs to be rebuilt, which can cost between $2,500-$4,000. Or worse, a total engine replacement, which can reach as high as $10,000 or more

Knock sensor replacement costs are more moderate: The cost can range from $200 to $800, but it could be more or less depending on the vehicle’s specific make and model and the repair shop’s location.

Why Professional Diagnosis Matters

Driving with a knocking engine noise isn’t safe and is a risk you shouldn’t take. While your car might still run with a knocking engine, it’s a warning sign of serious trouble brewing under the hood. The longer you keep driving, the more engine damage you risk, and it won’t be long before things go from bad to worse.

Similarly, engine misfire symptoms should not be ignored because misfiring cylinders strain the engine and decrease fuel economy over time.

For residents in the Athens area seeking professional diagnosis and repair, experienced Engine Repair Services in Athens, GA can provide the expertise needed to properly identify and address these complex issues. Pro Transmissions, a family-owned business with over 30 years of combined expertise, specializes in comprehensive engine diagnostics and repairs for American, Japanese, classic, and muscle cars.

Prevention and Maintenance

Regular maintenance is key to preventing both misfires and engine knock. This includes:

• Using the correct octane fuel as specified in your owner’s manual
• Regular spark plug replacement
• Maintaining proper oil levels and quality
• Addressing check engine lights promptly
• Regular engine tune-ups and inspections

Understanding the difference between engine misfires and engine knock can help you communicate more effectively with your mechanic and make informed decisions about repairs. While both issues require professional attention, early diagnosis and proper repair can prevent more costly damage and keep your vehicle running safely and efficiently.