What Causes An Engine To Backfire - Service Research from Carr Chevrolet

An engine backfire occurs whenever the air-fuel mixture in your car combusts somewhere outside the engine's cylinders. This can cause damage to your car's exhaust or intake if left unchecked -- and it also means that your car's engine isn't making as much power as it should, and is wasting lots of fuel. A car that backfires consistently is therefore urgently in need of repair!

The last thing you want is for your whole car to go out with a bang, so head to Carr Chevrolet in Beaverton for expert service if your car is backfiring. On this page, our expert technicians have gathered four things that commonly lead to engine backfiring.

This engine has sustained major damage, and one if the valves is broken inside the cylinder.

4. Bent Valve Or Valves

Inside each of your engine's cylinders, you'll find at least one intake valve and one exhaust valve. They're designed to let air and fuel into the cylinders, then shut when combustion occurs. Then, once the air and fuel has been combusted, the exhaust valves open to let the exhaust fumes out the tailpipe.

However, if the valves become bent, they won't form a proper seal. That'll allow air and fuel to flow back into the intake or into exhaust, where it will combust. Luckily, this is a very uncommon reason for a modern car to start backfiring. Replacing bent valves and/or bad valve seals can be a costly procedure, as it means dismantling the entire engine.

A technician adjusts the timing belt on this engine.

3. Bad Ignition Timing

Once both sets of valves are closed, that's when the spark will fire inside the cylinder -- or at least that's when the spark is supposed to fire. However, if the spark timing isn't just right, the spark could fire too early before the intake valves are closed, or too late when the exhaust valves have already opened. When this happens, the air/fuel mixture in the exhaust or the intake can combust, leading to a backfire. Since the spark timing in a modern car is computer controlled, this is a problem that'll need to be addressed by a trained technician.

A severely lean or rich air/fuel mixture can cause the check engine light to turn on.

2. Rich Air/Fuel Mixture

For various reasons like leaking fuel injectors or a clogged engine air filter, the engine might have too much fuel added to the cylinder, or not enough air. For proper combustion, the exact right ratio of air to fuel must be maintained. A mixture of air and fuel that's got too much gas in it is called, "rich." When a rix air/fuel mixture is ignited in the cylinder, the whole mixture won't be burned up by the time the exhaust valves open. Then, the combustion process will flow to the exhaust where a backfire will take place. Getting a rich air/fuel mixture fixed means replacing bad fuel injectors, a bad mass airflow sensor or even something as simple as replacing the air filter.

1. Lean Air/Fuel Mixture

Not only can a rich air/fuel ratio cause a backfire, a mixture that doesn't have enough gasoline can cause a backfire, too. A "lean" mixture is one that doesn't have enough fuel, and too much air. Such a mixture could be caused by low fuel pressure due to a failing fuel pump, a clogged fuel filter or clogged fuel injectors. When a lean mixture combusts, it burns more slowly, meaning there will still be some air and fuel that isn't used up when the exhaust valves open -- leading to a backfire. You'll want to have a Chevrolet technician take a close look at your vehicle's fuel system if the air/fuel mixture in your engine is running lean and causing backfires.

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  1. CARR Chevy World

    15005 SW Tualatin Valley Highway
    Beaverton, OR 97006

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