5 Reasons that Cause Your Car Backfire – Diagnosis and Troubleshooting

Why does a car backfire? It is actually a process where one or more spark plugs ignite the fuel in their cylinder, which has an open exhaust valve, out of turn. To put it simply, backfiring happens when the fuel combustion happens out of the internal combustion chamber. You will know it when your car produces screeching sound when it stops and releases fire or some smoke from the tailpipe when it starts again. To find out what makes a car backfire and what should we do to solve this problem, let’s roll up our sleeves and start now!

What Cause a Car to Backfire: 5 Reasons behind the Problem

Car backfiring is not alarming as long as it involves only screeching sounds. The noise indicates that the vehicle is out of tune and is performing poorly. However, you have a legitimate reason to worry if there is smoke. Let’s know about 5 reasons that cause car backfire.

1. A High Fuel-to-Air Ratio

Sometimes, the engine gets the supply of fuel more than it can burn. This condition is known as ‘running rich.’ When an engine runs rich, it burns fuel slowly, causing the extra air to forcefully burn the unburned fuel and spit out when the exhaust valve opens. A dirty air filter is a reason for this problem to happen in most cases.

car backfiring
Smoke coming out of the tailpipe is not good news. Source: Wallpaper Cave

2. Broken Distributor Cap

Broken Distributor Cap is one of the answers for the question “What cause a car to backfire”. Some car models don’t have ignition coils on the spark plugs. They distribute electrical pulses across spark plugs by the use of a distributor cap and a set of wire. These pulses are instrumental in making the spark plugs to produce the sparks that ignite the fuel.

A broken or damaged distributor cap allows moisture to leak in that causes a spark from one cylinder to fire out another cylinder. It disrupts the synchronization of the sparking and causes a car backfire.

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3. Inaccurate Engine Timing

Also known as retarded timing, it indicates that the engine cycle of fuel-compression-ignition-exhaust in the cylinder head is out of sync with the bottom part of the cylinder. Due to this problem, the ignition cycle begins late in the combustion chamber, causing the burnt fuel to come out with force when the exhaust valve opens.

4. Carbon Tracking

When talking about what makes a car backfire, we have to think about carbon tracking. Carbon tracking can happen to all types of vehicles – the models that use distributor cap and the ones that have ignition coils. In an old vehicle with a distributor cap, the sparks can go crossways from one wire to another due to environmental factors. In case if it becomes a regular phenomenon, a carbon that functions as a shortcut to the spark will make the car to backfire.

car backfire
Older vehicles could backfire due to worn out parts. Source: Hemmings Motor News

The vehicles that have ignition coils will show almost similar symptoms. The sparks will transmit through the wrong route, making the number of sparks left in the cylinder inadequate for burning the fuel. The next ignition will be sufficient to fire the plug but it will require more fuel in the cylinder this time. It will create a rich fuel situation and cause a backfire.

5. Worn out Air Gulp Valve

Vehicles manufactured in the early 2000s or before that period are likely to have an air injection unit with an air gulp valve. The valve is the passageway for air to enter the system when the engine is under load. When it’s malfunctioning, it releases air into the combustion chamber even at the time of de-acceleration. It creates the ignition of unburnt fuel and causes a car backfire.

Car Backfire – Diagnosis and Troubleshooting

When backfires suddenly happen in your car, you should do the the below troubleshooting inspections with 5 steps here:

Step 1: Examine the Engine Warning light

dashboard engine light
When your engine backfires, the first step you should do is checking the engine warning light. Source: Jim Larrison/Flickr

Checking the engine warning light is the first thing you should do when you find out backfiring in your car. According to auto experts, most of cases causing car backfiring will make the engine warning light of the car to turn on.
In case your car doesn’t show any sign in engine warning light, step 2 is exactly what you should do.

Step 2: Inspect the Upstream Exhaust Leak

Upstream exhaust leak cause backfire
Inspecting the upstream exhaust leak to make sure there is no exhaust leak. Source: Automotivebros

If un-burnt fuel meets air in the exhaust system, it will burn, causing the screeching sound of a backfire. Thus, you need to check the upstream exhaust leak to clear the air of any suspects.

Normally, people often think that the exhaust system works under pressure constantly to eliminate waste gasses from the car engine. But actually this is wrong. Each car engine system contains many pressure pulses and vacuum which are brought about by the expulsion of the combustion charge concurrently with the exhaust valve opening and the closing of the same valve. This form a vacuum event forcing fresh air into the exhaust system (causing the car backfiring). Therefore, you have to seal any leaks to make sure that there is no exhaust leaks.

Step 3: Check the Gulp Valve

Most engines have 1 or 2 air gulp valves (i.e one air gulp valve for every exhaust manifold). To check the condition of the valves, you should remove then blow into them from each inlet/outlet.

As air will flow one way in a good valve, if you observe air flows in both ways, the valve is broken and it’s time to replace it. To buy replacement valves, you can go to a nearby repair workshop or buy them from online shops.

Step 4: Check the Spark Plugs

Every car has an ignition system which is triggered by an electronic pulse signalling the ignition coil to fire. If your engine’s ignition system is working well, the resistance in the system will be calibrated into the system.

But if there is something wrong with the resistance, it will result in failure in the ignition system, causing the car crossfires into the wrong cylinder. Inbuilt computer can not detect the problem, therefore the Check Engine Light may not turn on.
To avoid this unexpected case, auto experts recommend you should change spark plugs regularly and always check them when you go for service.

Step 5: Inspect your air sensor

Broken mass air flow sensor cause car backfire
Bad air sensor results in car backfiring.

Each car has an on-board computer which inspects and collects data on the air entering the engine constantly. All this process is done through the mass air flow sensor. The on-board computer will get the incorrect readings if there are some problems with the sensor, which will happen when the sensor cokes. Getting inaccurate data will make the computer result in a lean mixture condition which isn’t enough to turn the check engine light.

To fix this problem, you are recommended to remove and clean the mass airflow sensor. In case the sensor is totally broken, you will need to buy a new one.

Final Words

A backfire appeared in your exhaust pipe can not hurt your beloved car immediately, but it can be a warning sign of a coming problem or a indicator to a more awkward issue. Learning about what cause a car to backfire and always ensuring that your vehicle is running optimally by maintaining it regularly is what you should do in order to prevent any unexpected problem.

Did you enjoy our article? Feel free to share this article with your friends and in case you have any question like “why do cars backfire” or “What causes a car to backfire on acceleration”, leave it in the comment box. Let’s keep the conversation going on!