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Can a Bad Alternator Cause a Misfire?

Hi, I'm Azim Uddin, a student who loves cars. Visit to learn about car maintenance for beginners and experts. In my studies, I found a cool connection between hosting and car care. Join me on this journey where every road has a story, and hospitality meets the thrill of cars. Explore, learn, and enjoy the ride with me!

Hi, I'm Azim Uddin, a student who loves cars. Visit to learn about car maintenance for beginners and experts. In my studies, I found a cool connection between hosting and car care. Join me on this journey where every road has a story, and hospitality meets the thrill of cars. Explore, learn, and enjoy the ride with me!

Last Updated on May 10, 2024 by Azim Uddin

From engine stalling to dead battery, a bad alternator can cause several issues with the vehicle parts. But what about misfires? Can a bad alternator cause a misfire?

Yes, a bad alternator can indirectly cause misfires on some rare occasions. Due to a lack of power and unusual voltage fluctuations caused by a bad alternator, the spark plugs and ignition system lead to misfires. Similarly, it can cause misfires by influencing the fuel system and engine parts.

Let’s dive in and find out how a bad alternator can cause misfires and how to easily fix it. I’ll also share the other symptoms of a malfunctioning alternator and ways to diagnose it.

Can a bad alternator cause a misfire?

How Does a Bad Alternator Cause a Misfire?

In general, misfires are caused by the improper proportions of air and fuel required for combustion. Components of the fuel system, ignition, and ECU are mainly responsible for misfires.

However, in some rare cases, a bad alternator can also cause these components to malfunction. Here’s how the alternator creates a misfire:

Low Voltage and Weak Battery

Although the battery powers the entire vehicle, the alternator is essential to charge the battery. When the alternator goes bad, it fails to charge the battery adequately.

The inconsistent voltage and power supply eventually affect the spark timing and combustion, resulting in misfires.

Insufficient Power to the Spark Plugs

The alternator supplies power to the ignition system. It’s necessary for the coil that generates the spark for the plugs.

See also  What Causes Car Engine Misfire At Low RPM? Let’s Find Out!

A bad alternator can’t provide enough voltage for the coil to generate a strong enough spark. Therefore, when the vehicle is under load or accelerating, it misfires.

Spark Plug
Spark Plug Diagram

Faulty Sensor Readings

Inconsistent voltage from a failing alternator can disrupt the readings of the crankshaft or camshaft position sensors. This way, the ECU gets the wrong data and adjusts the fuel-air mixture parameters accordingly to create misfires.

Interference with Electronic Control Modules (ECMs)

After collecting the data from the sensors, the Electronic Control Modules or ECMs send them to the ECU for processing.

Voltage fluctuations caused by a bad alternator can interfere with the proper functioning of the ECMs. It leads to misinterpretation of sensor data and subsequent misfires.

Common Causes of Engine Misfire

As mentioned, misfires are rarely caused by a bad alternator. So, before you blame it, inspect the following parts first:

Failure of the Ignition System Components

In most cases, misfires are caused by issues with spark plugs, ignition coils, related wires, or the distributor.

Worn spark plugs can’t generate sufficient spark, leading to incomplete combustion in the cylinder. Similarly, damaged ignition coils or wires result in inconsistent sparks and cause misfires.

Air Intake and Vacuum Leaks

Due to air or vacuum leaks, unmetered air enters the engine and creates an improper air-fuel mixture ratio. Too rich or too lean mixtures cause the engine to misfire.

Common sources of leaks include cracked intake manifold gaskets, vacuum hoses, or the intake manifold itself.

Malfunctioning Fuel System Parts

Clogged or dirty fuel injectors alter the fuel spray pattern and affect the combustion process.

A malfunctioning fuel pump and restricted fuel filters fail to deliver sufficient fuel to the engine, resulting in lean conditions and misfires.

Failed Sensors

Faulty sensors such as the crankshaft and camshaft position sensors or mass airflow sensors provide inaccurate data to the ECM. As a result, the engine runs lean or rich on the air-fuel mixture, leading to misfires.

See also  Engine Misfire at High RPM? Diagnosis and Solution

Other Symptoms of a Bad Alternator

So, how do you know your vehicle’s alternator isn’t working without going to a mechanic? To understand whether a bad alternator causes a misfire, look for the following symptoms of alternator malfunction:

Illuminated Warning Lights

Most modern vehicles are equipped with sensors to detect charge or battery issues. Therefore, when the alternator goes bad and the voltage fluctuates rapidly, a battery warning light on your dashboard will illuminate.

It’s often shaped like a battery or indicated by the word ‘ALT‘ or ‘GEN‘.

Lack of Battery Charge

The alternator converts mechanical energy to electricity to charge the battery. So, any problem with the alternator will directly affect the battery and drain its charge more frequently.

Dimming or Flickering Lights

Without a proper supply of electricity, the headlights, interior lights, taillights, and dashboard of your vehicle will lose power and start dimming or flickering.

Similarly, the reduced voltage will affect other electrical parts including the radio, power window, and dashboard gauges.

How to Diagnose a Bad Alternator?

If you notice any of the above-mentioned symptoms, you’ll have to diagnose it before getting a replacement. You can use a multimeter to diagnose a bad alternator. Here’s how:

  • Locate the cylinder-like alternator on the side of the engine. It has a small fan on the side for cooling. Set the DC voltage of the multimeter to 15-20V.
  • Connect the positive prong of the multimeter to the red-colored testing terminal of the alternator. Attach the negative prong to a metal part of your vehicle.
  • Now, turn the engine on. If the voltage reading is not within the range of 13 to 15V, the alternator has failed.

How to Fix a Bad Alternator?

Depending on the condition of the alternator, you can either get new parts or replace the whole alternator. Here’s what you need to do:

  • Take off the battery terminals first and disconnect the electrical wires from the alternator. Remove the serpentine belt and mounting bolts to take off the alternator.
  • Unscrew the plastic cover from the alternator, test the bearing, and replace it if it’s not fitting snugly. Now, take off the resistor and replace the rectifier.
  • Inspect the brush assembly and change the springs if necessary. Do the same for the voltage regulator, wires, and other components of the alternator.
  • Once you’ve replaced all the worn or damaged components, reinstall the alternator and test it with a multimeter.
See also  Why Does Your Car’s Engine Misfire At Idle? Let’s Find Out!

If your vehicle is experiencing a misfire, you might find our article on ‘Why Does Your Car’s Engine Misfire at Idle?’ beneficial in comprehending whether a faulty alternator can be the underlying cause. Our comprehensive guide on engine misfire at idle provides an in-depth exploration of the common causes behind your car’s engine’s misfiring during idle moments. Meanwhile, our piece on engine misfire at high RPM delves into everything you need to know about this issue.


Now, let’s take a look at some common queries regarding a bad alternator causing misfires.

Q. How long can I drive with a bad alternator?

If you have a full battery charge, you can drive anywhere for a few days with a bad alternator. With a low battery charge and a fully failed alternator, the vehicle will run only for a few hours.

Q. Can I diagnose a bad alternator with a scanner?

Yes, you can use an OBD-II scanner tool to diagnose a bad alternator. In most cases, you’ll get a P0562 or P0620 code indicating low voltage and bad alternator.

Q. Do I need a new battery after replacing the alternator?

No, you don’t need a new battery after replacing the alternator. If your battery is in good condition, a bad alternator won’t affect it. However, you can consider a replacement if the battery is too old.

Wrapping Up!

While a bad alternator can cause a misfire, it typically depends on the condition of the battery. Even without the alternator, the battery can supply the necessary power for the vehicle for some time.

However, once the battery drains and the alternator isn’t charging it, the engine will start misfiring while starting or accelerating. To avoid this, replace the alternator at regular intervals as suggested by the manufacturer. Also, avoid harsh driving conditions and properly charge the battery to prevent such misfires.

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