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I’ve made this site for non-technical drivers who are experiencing problems with their cars.
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Published date: October 25, 2021
Updated date: February 27, 2024
Reading time: 8 min
This article was fact checked
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It is very unusual for a bad alternator to cause a misfire.
The alternator is responsible for powering electrical components while the engine is running. It doesn’t control the firing sequence inside the engine.
As you can see, there is little crossover between the alternator being bad and your car misfiring.
However, if your car is misfiring, and you’ve investigated all the likely causes, here are some things you should try.
It’s possible that the alternator is intermittently grounded. The word here is intermittently. If it wasn’t grounded at all it would be more obviously a grounding problem. One way to check it’s not the alternator for sure is to disconnect it very briefly and see if that fixes the problem.
Just be sure your battery has enough power to run your car for ten minutes without an alternator. Turn off all lights, radio, and aircon too. If there is no misfire when you have the alternator disconnected, then your alternator – or its grounding – is at fault.
The alternator powers the crank position sensor. If that is giving the ECU a bad signal, it might not fire the coil, resulting in a misfire.
A video on How To Ground Your Alternator will help you out.
https://youtu.be/esNkEoDdVHk
Another way of trying to diagnose the issue would be to while your engine is running, disconnect your battery and see if the problem persists. Also, check your battery’s voltage levels are consistent – this goes for the overall voltage in the system, too.
Hook your car up to an OBD reader and look for error code P0562. This is a code for a bad alternator.
Have a mechanic take a look at your O2 sensors and ECU (Engine Control Unit). Even if the alternator is functioning properly, a problem with either of these components can cause issues in the air-fuel mixture in the engine. This could be a very likely cause if all other electronics are functioning well.
Lastly, check your wire harness. Since this is responsible for carrying electricity to the systems that require them, a malfunction can spike further and cause problems with the spark plugs, sensors, or the ECU.
Other More Probable Misfire Causes
A Clogged Fuel Injector
When an injector is clogged, the right amount of fuel doesn’t mix in the combustion chamber. Air will fill the larger share of volume in that cylinder – this is known as running lean.
Defective Vacuum Seal
This can lead to decompression in the chamber, causing problems with the combustion process.
A loss of pressure or extra air caused by such a leak can cause a misfire.
A similar cause could be faulty exhaust-gas circulation. If the exhaust gases don’t exit the system properly, or if their flow is hindered by a clogged exhaust pipe/catalytic converter, they can cause problems with the sensors in the car.
The result is a misfire.
Cost: Anywhere between $200 to $1500 or above, depending on the type and degree of fault in the engine
Bad Spark Plugs
With the evolution of electronic ignition systems, an average spark plug’s life has drastically increased. What used to be a service life of 12,000 miles has increased to 100,000 miles or more.
However, they’re not immune to wear and tear and can collect deposits that prevent them from firing at full strength, possibly leading to a misfire.
The average replacement cost for a full set is $200 – $400
The spark plugs may not be the only culprit.
Even before your car’s spark plugs get to fire a spark, other parts play a role in making it happen too. These include coils, onboard sensors for the computer, and extensive related circuitry.
When the engine is switched off, the battery usually carries the load of the electrical systems; when it’s on, the alternator takes over and also re-charges the battery.
The alternator could cause your spark plugs and other electronics to malfunction, which could lead to a misfire, but it directly being the cause is unlikely.
Also, a failing alternator will reveal itself in other electrical components much more visibly than bad coils and spark plugs (which are suspected of causing the misfire).
Common Signs That The Alternator Is Defective
Headlights Dimming and Brightening.
The fluctuating voltage may cause this as the alternator struggles to maintain a steady voltage.
Stalling or Difficulty Starting the Engine
These are typical problems caused by a bad alternator, with the former being more common.
This is due to your alternator not powering the spark plugs and coils adequately.
Alternatively, it may not be charging the battery sufficiently.
The smell of burning rubber or wires may indicate that parts of the alternator are experiencing wear.
Since the drive belt on the alternator is exposed to the engine’s heat, its rubber may start to burn.
Frayed or worn wires may overheat because of an overworking alternator and heat up, giving the distinctive smell of burning plastic.
Conclusion
It’s rare for the alternator to cause misfire problems. However, if you have addressed and troubleshot all more likely causes then it’s worth exploring the possibility.
The alternator not being grounded to the engine block is the most obvious check to do. Even better news as it’s the connection rather than the alternator it’s very cheap to put right too.
Thanks for coming to my site. In case we haven’t met yet, I’m Kevin and I just love passing on my 30 + years of experience repairing and maintaining cars.
I’ve made this site for non-technical drivers who are experiencing problems with their cars.
