Car is Loud When Accelerating: Cause, & Fixes

Every car owner expects their vehicle to run smoothly when they turn the key and press the accelerator. However, sometimes the engine stumbles, hesitates, or misfires, leading to a rough ride and potential long-term damage. One of the lesser-known causes of engine misfires is bad fuel.

Fuel quality plays a crucial role in how well an engine operates. Contaminated or poor-quality gas can cause various performance issues, from rough idling to stalling. Many drivers overlook the impact of fuel quality, assuming misfires are solely due to spark plugs or ignition system faults.

But bad gas can absolutely cause an engine to misfire by disrupting combustion and preventing the engine from running efficiently.

This guide explores how bad fuel leads to misfires, signs to watch for, and how to fix the issue before it causes lasting damage to your engine.

Table of Contents

What Is an Engine Misfire?

An engine misfire occurs when one or more cylinders fail to ignite properly. This results in a loss of power, rough performance, and increased emissions. Misfires can happen occasionally (random misfires) or consistently (persistent misfires), depending on the cause.

Common Symptoms of an Engine Misfire:

Rough idling – The engine shakes or vibrates while at a stop.
Hesitation or jerking – The car feels sluggish when accelerating.
Loss of power – Reduced performance, especially under load.
Check engine light (CEL) illuminated – The car’s computer detects improper combustion.
Increased fuel consumption – Inefficient burning of fuel wastes gas.
Unusual exhaust smell – Fuel that isn’t burning properly can produce a strong odor.

Now that we understand misfires, let’s see how bad gas plays a role in causing them.

How Can Bad Gas Cause a Misfire?

Bad fuel affects combustion by disrupting the air-fuel mixture, reducing fuel efficiency, and harming engine components. Here are the primary ways poor-quality gas leads to misfires:

1. Water Contamination in Fuel

Water in the gas tank can cause misfires because water does not burn like gasoline. When water gets into the fuel system, it prevents proper combustion, leading to rough engine performance.

Causes of Water in Gasoline:

Condensation inside the fuel tank.
Refueling at gas stations with contaminated underground storage tanks.
Improperly stored or old gasoline.

Signs of Water-Contaminated Fuel:

Hard starting or failure to start.
Engine sputtering or stalling.
Reduced power and acceleration.
Visible water separation in the fuel sample.

2. Low-Quality or Old Gasoline

Gasoline degrades over time. If you use old or poor-quality fuel, it loses volatility, meaning it won’t ignite properly in the engine. This can cause misfires, rough running, and difficulty starting.

Causes of Low-Quality Fuel:

Buying gas from stations with poor fuel turnover.
Storing fuel in a vehicle for extended periods without use.
Using fuel that contains excessive ethanol (which absorbs moisture).

Signs of Old or Stale Gasoline:

Hard starting, especially after long periods of inactivity.
Noticeable drop in fuel economy.
Weak acceleration and poor throttle response.
Strong varnish-like odor from the fuel tank.

3. Excessive Ethanol Content in Fuel

Most gasoline sold today contains ethanol, which helps reduce emissions. However, too much ethanol can cause engine misfires because ethanol absorbs moisture and burns differently than pure gasoline.

Problems Caused by High Ethanol Content:

Lean air-fuel mixture – Too much ethanol can throw off the fuel mixture.
Corrosion of fuel system components – Ethanol attracts moisture, leading to rust.
Fuel separation – Ethanol and gasoline can separate over time, reducing fuel quality.

Signs of High Ethanol Fuel Issues:

Hard starts, especially in cold weather.
Hesitation or surging during acceleration.
Poor fuel economy due to improper combustion.

4. Dirty or Clogged Fuel Injectors

Bad gas often contains dirt, debris, or sediments that clog fuel injectors. When injectors get clogged, they don’t spray fuel evenly, leading to an unbalanced air-fuel mixture and misfires.

Causes of Dirty Fuel Injectors:

Fuel purchased from low-quality gas stations.
Old gasoline that leaves deposits.
Poor fuel filtration due to a failing fuel filter.

Signs of Clogged Injectors:

Uneven engine performance.
Delayed throttle response.
Noticeable engine misfires under load.

5. Fuel Octane Rating Too Low

Some vehicles, especially those with turbocharged or high-performance engines, require premium fuel (91 or 93 octane). Using lower-octane fuel in these vehicles can cause knocking, pre-detonation, and misfires.

Effects of Using Low-Octane Fuel:

Increased combustion temperatures.
Engine knocking or pinging.
Loss of power and reduced efficiency.

How to Fix a Misfire Caused by Bad Gas

If you suspect bad gas is causing a misfire, here’s what you can do:

1. Add a Fuel Additive or Octane Booster

Fuel system cleaners help remove deposits from injectors.
Water removers (like ISO-HEET) absorb excess moisture.
Octane boosters improve combustion in engines requiring higher octane.

2. Drain and Replace Bad Fuel

If the fuel is contaminated, it’s best to drain the tank completely and refill it with fresh, high-quality gasoline.
Dispose of bad fuel properly to avoid environmental harm.

3. Replace the Fuel Filter

A clogged fuel filter can restrict fuel flow, leading to misfires.
If you’ve been running poor-quality gas, replacing the fuel filter is a good preventive measure.

4. Clean or Replace Fuel Injectors

Use a fuel injector cleaning solution to remove buildup.
In severe cases, injectors may need professional cleaning or replacement.

5. Use High-Quality Gasoline

Always buy gas from reputable stations with a high fuel turnover.
Avoid using cheap, unbranded fuel, as it may contain contaminants.
If your car requires premium fuel, stick to the manufacturer’s recommendation.

How to Prevent Fuel-Related Misfires in the Future

To avoid future misfires caused by bad gas, follow these best practices:

1. Always Use Fresh Fuel

If a vehicle sits unused for long periods, use a fuel stabilizer to prevent gas from going bad.

2. Stick to Trusted Fuel Brands

Major fuel brands often add detergents that keep the engine clean and prevent deposits.

3. Check for Water Contamination

If you suspect water in the gas, use a fuel additive or have the tank checked by a mechanic.

4. Keep Your Fuel System Maintained

Regularly replace the fuel filter and inspect the injectors for buildup.

Yes, bad gas can absolutely cause engine misfires. Contaminated, stale, or low-quality fuel disrupts combustion and affects engine performance. Issues like water contamination, ethanol imbalance, dirty fuel injectors, and incorrect octane levels all contribute to misfires and rough engine behavior.

If your vehicle starts misfiring after refueling, consider fuel additives, draining the tank, or replacing the fuel filter to fix the problem. Preventing bad fuel issues by choosing high-quality gasoline and keeping the fuel system clean is the best way to ensure a smooth-running engine.

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Stephen Madison

Stephen Madison is a well-known automotive writer with over ten years of experience. A lifelong car lover, Stephen writes about cars in a way that is both easy to understand and exciting. At Vehicle Grip, Stephen writes about everything from car reviews to the latest automotive innovations. With a background in mechanical engineering, He has a deep knowledge of how cars work. This helps Madison explain complex car technology in simple terms that everyone can enjoy.