Help! My Car is Backfiring!

no backfiring
This is one way to control the backfire in your car's exhaust. Getty

On the stage of automotive ownership, there are a few characters you are not interested in playing. The guy who drives over the parking block and the girl who thinks her car is in Reverse when it’s actually in Drive are near the top of the list. Close behind is something that occurs not out of absent-mindedness, and can be remedied — the exhaust backfire. If you’ve ever heard a truly loud engine backfire, you know it can only be compared to a gunshot in volume and its ability to startle everyone around.

That startling feeling is usually followed by dirty looks, and for the driver who owns the backfire, some level of shame for having severely disturbed the peace.

What is a Backfire?

A backfire is a loud bang that comes from your exhaust pipe. It can happen anytime, but usually occurs when you are trying to start the engine, or when you take your foot off the gas pedal as the engine RPMs are coming down. A backfire occurs when unburned fuel makes its way out of the engine, but ignites someplace in the exhaust system. This may be happening right at the engine, or later down the line past the resonator. The small explosion that is supposed to be happening inside one of your cylinders with the valves in the close position is escaping, and so is all the noise. 

Can a Backfire Damage My Engine? 

In almost all cases, there is no specific danger related to a an engine backfire now and then. If you have any weakness in your exhaust system, like a loose joint, rusted area, or bad gasket, a backfire will usually bring this to light and force your hand in terms of repairs.

Not only is a backfire loud, it can be fairly powerful. This blast of force can cause a weakened exhaust system to fail. In some vehicles, a backfire can also occur through the intake rather than the exhaust. This type of backfire can damage plastic intake components like the airbag or intake piping.

This type of backfire is more rare.  Any backfires are the sign of an engine that needs some tuning or repair work.

What Causes an Engine to Backfire?

There are a number of conditions that can result in a backfire. The basic principle is the same - unburned fuel is igniting somewhere in the exhaust system, but the causes can be varied. 

  • Poorly Set Ignition Timing. If your vehicle has manually adjustable ignition timing, a setting that is off by a few degrees can be enough to cause a backfire. Set the timing and see if things get better. Most new vehicles do not have timing that can be adjusted manually, but could be suffering from a failing ignition module or computer that is causing the same timing issue. 
  • Incorrectly Placed Plug Wires. If you've ever mixed up your spark plug wires, as in your removed them and didn't put them back in the right order, you could hear some serious backfiring. If you just had your plug wires disconnected, and your first attempt to start the car resulted in a huge backfire, check the plug wires first. 
  • Improper Valve Timing. A valve that has been adjusted really badly can leave enough of a gap to cause a backfire. For that matter, a broken or badly worn valve or camshaft can cause the same condition. This is a worst case scenario, so don't jump on valve timing right away. If your vehicle has electronically controlled variable valve timing, check the electronics, too. 
  • Slipped Timing Belt. A timing belt has teeth on it that need to be in just the right place on the cam gear or gears. If it's off by a single notch, your engine won't run properly and can even backfire. A valve timing check should tell you if your timing belt is so out of whack that you can't time the engine properly.