Why Do Engines Backfire?

Have you ever heard an engine backfire or currently have your engine backfiring and wonder what causes this to happen?  This article is designed to explain the most common engine backfire causes and what can be done to fix this issue.

Why Is My Engine Backfiring?

An engine backfire is when an internal combustion engine causes an explosion that occurs either in the air intake or the exhaust system instead of within the engine cylinder combustion chamber as designed.  This will usually be accompanied by a loud bang that will come from your engine and exit through your exhaust.

If an engine backfire does occur in the exhaust system this is called an afterfire because it is coming after the combustion process of the engine.  Most people will still call this type of issue an engine backfire.

What Are Some Common Engine BackFire Causes?

There are two ways that your engine can backfire either up back into the air intake of your engine or out in the exhaust system leading from your engine.  I’ve included the most common issues that can cause this to happen on your car’s engine.

1. Your Engine Is Running Rich

If your engine is running rich this means that it is injecting more fuel into the cylinder of your engine than can be burned off during the combustion process.  When this happens the unburnt air and fuel mixture can be ignited in the exhaust chamber and shoot out of your car through your tailpipe. This will typically be accompanied by a loud bang from your exhaust and can also cause flames to shoot out of your exhaust tailpipe.

2. Bad Ignition Timing

If your intake valve is still open when your spark plug ignites this will cause the spark plug to ignite the air and fuel mixture and shoot that out of the air intake port back towards the carburetor of your engine.  If you have a newer vehicle then you probably do not have a carburetor and will instead have an electronic throttle body. Backfiring your engine back through the air intake is going to be less likely to occur with an electronic fuel injected system.

3. Your Spark Plug Wires are Not Connected Properly

Your spark plugs are connected to your engine’s cylinders in a specific order as the engine is designed to fire the cylinders in a specific order that is determined by the engine manufacturer.  If you replace your spark plug wires and accidentally mix up how they are wired to the individual spark plugs this can cause your engines spark plugs to spark out of sequence which can lead to your car backfiring.  

If cylinder one is supposed to be sucking in the air into the cylinder but the cylinders spark plug ignites during that process this can cause your engine to backfire back through the carburetor.

This same issue can also occur on the exhaust side where if the cylinder is supposed to be pushing out the old air and fuel mixture but instead sparks while the exhaust valve is open it can cause your engine to backfire out of your exhaust pipe.

This is why it is advised that if you plan to replace your spark plug wires on your car that you do them one at a time as to not get the wires mixed up and accidentally connect them to the wrong spark plugs on your engine.  On more modern cars they come with coil packs which eliminate the need for spark plug wires.

How Can I Stop My Engine From Backfiring?

1. Check Your Spark Plugs

If your engines spark plugs are not able to fully burn the air and fuel mixture in the cylinder this can cause the air-fuel mixture to ignite in the exhaust manifold causing a backfire.  If you are unsure of when your spark plugs were last replaced it would be a good idea to inspect them for carbon buildup and corrosion.

If they do have a lot of carbon buildup on them it would be a good idea to go ahead and replace all of the spark plugs on your vehicle to eliminate this as a cause of your engine backfiring.

If you are looking to replace your spark plugs and you are not sure about which type of spark plugs that you want to go with I’ve written an article outlining the differences between iridium and platinum spark plugs.

What’s Better Iridium versus platinum spark plug article

2. Check Your Spark Plug Wires

If your vehicles spark plugs are worn out and are not sending enough charge to the spark plugs in your engine this can cause the air/fuel mixture in your cylinder to not burn off all the way.  

As you now know this can cause your engine to backfire out of the exhaust system if there is unburnt fuel in the cylinder. If you suspect your spark plug wires to be bad you can always replace them with new spark plug wires, new spark plug wires for your car should not be that expensive and it’s a relatively easy process.  

It is advised that if you plan on replacing your spark plug wires that you do them one at a time to not get them mixed up in the process.

3. Check Your Distributor Cap

On older vehicles, with spark plug wires there will also be a distributor cap.  A distributor cap is what sends the electricity through your spark plug wires to your spark plugs that are mounted in your engine.  

Eventually, distributor caps can go bad and cause them to not send enough electricity through your spark plug wires to be able to fully burn the air-fuel mixture in your engine cylinder which can cause engine backfiring.  

If you suspect that your distributor cap to be the culprit you can replace your distributor cap relatively easy. You should be able to find a replacement distributor cap at your local auto parts store or online, just make sure that you buy one that is designed to fit your vehicle.

4. Check Your Carburetor

If your carburetor is sending too much fuel into the air intake of your engine this can cause your engine to backfire.  If you know how to adjust your carburetor on your car then you can adjust it to send less fuel into the air intake so that this no longer happens.  If you do not know how to do this yourself you may want to take your vehicle to a mechanic so that they could adjust it to correct this issue.

Sometimes stuff gets built up inside of engines carburetors which can also cause them to not operate as efficiently and they need to be cleaned.  If this is the case you can take some carb cleaner and an old rag to remove as much gunk and debris as you can to see if this helps out your situation.  Sometimes carburetors need to be eventually rebuilt or replaced altogether so also keep that in mind.

5. Check Your Fuel Injectors

If your fuel injectors are clogged up and not sending enough fuel into the intake of your engine this can also be a cause for your engine to backfire.  Checking your fuel injectors may not be that easy of a task as you may have to remove the fuel rail from your engine to check the fuel injectors if your engine.  

You could also try using a fuel injector cleaner in your gas the next time you go to fuel up your gas tank to see if this will help out. Some people have said that fuel injector cleaners have helped them out and some said that they were not helpful but it may be worth a shot.

 I personally use this Lucas Oil Fuel Treatment on my car to help keep the fuel injectors clean and help clean the fuel system.  Many people like this stuff a lot and use it every fuel change. They have reported that it helped with keeping the engine idling smoother, getting better MPG, and increased engine acceleration.  

It can be used in both gasoline and diesel engines.  To check out the current prices of 1 Gallon of Lucas Oil Fuel Treatment on Amazon click here.

6. Check Your Fuel Pump

If your fuel pump is going out or your fuel filter is clogged up your fuel pump may not be able to send enough fuel into the air intake of your engine cylinder.  This can also cause your engine to backfire. If you have never replaced your fuel filter before it may be a good idea to inspect and replace it if necessary. On my vehicle, this is not an option without replacing the fuel tank so it would be dependent on if that is possible on your vehicle.  

Your fuel pump could also be the culprit if it is old and not able to pump fuel into your fuel injectors as efficiently as it had when it was new.  If you start to hear weird whining sounds from the rear end of your vehicle (near the gas tank) when you go to start your vehicle your fuel pump may be going bad and would need to be replaced.

Common Engine Backfire Causes – In Conclusion

Hopefully, this article answered your question of why do cars backfire and presented you with some solutions and things to check if your car is currently backfiring and you want to get it fixed.  

If you are still having issues with your car backfiring after reading this article and checking out the solutions proposed here it may not be a bad idea to take your car to a mechanic so that they could look it over and determine the actual cause.