The causes of most engine backfires fall into two categories: gases explosively expelled through the intake manifold, or explosions that take place within the exhaust system. Backfires through the intake are generally related to problems with ignition timing, and backfires through the exhaust are usually related to fuel mixture problems. In most cases these problems are fixed through simple adjustments or minor repairs to the fuel or ignition system.
In order for an engine to run properly, spark plugs must produce a spark at the right time, or the fuel and air mixture will not be ignited properly. When ignition timing falls out of sync, the spark is produced at the wrong moment, which can result in the fuel being ignited while the intake valve is still open. This causes an explosion of the fuel and air mixture within the intake manifold, forcing the ignited mixture to exit from the carburetor or fuel injection intake.
Faulty Plug Wires
If spark plug wires are crossed or not installed on the correct spark plugs, the plugs will fire at the wrong time. This is similar to an ignition timing problem and causes the fuel mixture to be ignited while the intake valve is still open, resulting in the mixture explosively exiting from the intake manifold through the carburetor or fuel injection intake.
Vacuum Hose Leak
Leaking vacuum hoses allow excess air to enter the intake manifold. This upsets the air-fuel ratio and causes too much air to be mixed with the fuel, resulting in what is known as a lean running condition. The leaner fuel and air mixture is more volatile than the proper mixture and causes premature ignition, or pre-ignition of the mixture, resulting in backfiring through the tailpipe.
Proper engine operation relies on a precise amount of fuel mixed with a specific amount of air to produce a fuel-air mixture that will ignite properly in the combustion chamber. In modern vehicles, this fuel-air ratio is monitored and adjusted by onboard computers. Problems with one of the several sensors that the computer uses to monitor the engine, such as the oxygen sensor or airflow sensor, can cause the computer to misread the fuel and air mixture requirements of the engine. When this happens, the computer may not add enough fuel to the incoming air, resulting in pre-ignition and backfiring.
Weak Fuel Pressure
Weak fuel pressure caused by a failing fuel pump or clogged fuel filter results in too little fuel being added to the fuel-air mixture entering the engine. This causes a lean running condition in which the mixture has too much air in relation to fuel, which can lead to pre-ignition and backfires through the exhaust.
- Photo Credit exhaust pipe image by A74.FR Ben Fontaine from Fotolia.com
Why Does My Carburetor Backfire?
A carburetor backfire describes the small explosion that sometimes occurs when starting up a car. It generally makes a loud sound, like...
Jeep Backfire Problems
A backfiring automobile is certainly embarrassing, but a bigger concern is that it can also be a sign of problems with the...
How to Stop a Car From Backfiring
Backfiring is a common problem and can be a symptom of issues you need to address. The loud bursts of noise that...
How to Troubleshoot a Carburetor Backfire
Carburetor backfire can occur from time to time, and can be annoying. Generally a loud noise, which sounds like an explosion, is...
How to Tell What Is Wrong With My Car
Car problems can happen when you least expect them. While one car problem may be serious, another may be quite easy to...
How to Minimize the Exhaust Popping on a Harley
All exhaust popping or backfiring on a Harley-Davidson motorcycle is caused by fuel combustion in the exhaust manifold or the header pipes....
Scooter Backfires When Starting
Though all backfires may seem similar, all are not alike, and a variety of problems can ultimately cause a backfire. Two common...
My Stihl 250 Trimmer Backfires When Starting
A backfire ignites the fuel, or something else flammable, outside of the cylinder where it should be ignited. As gas runs into...
Why Does a Lawnmower Backfire?
When your mower backfires, it can be loud and sometimes scary. Backfire in engines is caused by simple chemical malfunctions that can...
Car Backfire Causes
When a car backfires, it means that something has stopped working properly in the emission system in the engine. There are a...
Troubleshooting a Backfiring Exhaust on a 350 Cubic Engine
Backfiring can cause serious damage to an engine if the problem is not quickly fixed. The problem can usually be traced to...