Reasons Engine Could Backfire - Subaru Service Questions in Olympia, WA

4 Things that Cause a Car Engine to Backfire | Auto Care Tips for Olympia, WA

It makes a loud sound and shoots flames out of the exhaust, so, what's not to love about an engine backfire? Well, for one, it's a sign that there's a significant problem with the combustion of your engine. At best, an engine that's backfiring will be losing a lot of wasted fuel. At worst? You could end up severely damaging the engine!

Luckily, most modern cars are computer controlled with exacting precision that makes engine backfires rare. But when one does happen on your vehicle, you'll want expert technicians to check your vehicle out and prevent it from happening again.

On this page, we'll explain a little bit more about what an engine backfire is and take a look at the four most common causes of an engine backfire.

Why does my Subaru's engine backfire
Schedule service for engine backfire in Olympia, WA

Why do Engines Backfire? Reason #1: Bad Engine Timing

An engine backfire is what occurs when the combustion event takes place outside the engine's combustion cylinders. Inside each cylinder, fuel and air are mixed in a precise ratio at the exact right time. A spark ignites the entire mixture, and the resulting explosions are what power your car.

If the timing of the spark is a bit too late in the engine cycle, unburnt fuel and air may be allowed to flow through the exhaust. As that ultra-hot fuel reaches the tailpipe, it mingles with the highly-flammable oxygen present in the outside air. This combusts the unspent fuel in the exhaust, rather than in the engine -- resulting in a loud bang and sometimes even visible flames coming from the exhaust tip.

Modern engine timings are controlled by computer, and can even vary on the fly. That means most engines will burn up 100% of the fuel in each combustion chamber each and every time. This kind of backfire is more common on older, carbureted engines with distributor caps.

Why do Engines Backfire? Reason #2: Rich Fuel Mixture

Modern engines can still backfire, and a poor fuel ratio is one common cause of this. For starters, let's imagine there is too much fuel in the engine and not enough air. The spark inside the chamber may not burn up all the fuel, allowing a little extra gasoline vapor to enter the exhaust, and lead to a backfire.

This can be caused by a faulty mass airflow sensor or a clogged engine air filter "choking" the engine and not allowing enough oxygen to flow into it. Or, it could be caused by leaking fuel injectors forcing too much fuel into the engine. You'll want to have these issues looked at by the professionals, otherwise you'll be wasting a significant amount of fuel.

Ask our technicians in Olympia, WA why your Subaru's engine could be backfiring

Why do Engines Backfire? Reason #3: Lean Fuel Mixture

The opposite problem can lead to the same result. If there's too much air in the cylinders at the time of the spark, and not enough fuel, the spark won't be able to ignite all the fuel at once. Yet again, leftover fuel vapor will flow into the exhaust and could combust there in a backfire.

Common causes of a lean fuel mixture include a vacuum leak allowing the engine to suck too much air; clogged fuel injectors not adding the correct amount of gasoline to the cylinders; or a bad fuel pump that's no longer pumping enough fuel from the tank to the engine.

Why do Engines Backfire? Reason #4: Older Engine Problems

If you've got a classic ride, that older engine technology under the hood is more prone to backfiring. That's because the systems on older engines aren't computer controlled, and thus will need constant adjustments often called a tune-up.

For example, modern cars no longer have spark plug wires. They're equipped instead witn coil-on-plug designs that increase the consistency and control with which the engine fires its sparks. On an older car with spark plug wires, wires that get crossed or installed in the wrong order can inadvertently cause a spark to fire in a cylinder when it's not supposed to. This could cause a significant backfire.

Additionally, classic cars featured carburetors rather than direct fuel injection. If the carburetor needed service or wasn't working correctly, it might not spray the right amount of fuel -- leading to an incorrect air-fuel ratio and, you guessed it, an engine backfire.

We're glad to have modern technology making things simpler and more reliable under the hood -- but if your car is backfiring, turn to the pros at the Hanson Subaru service center. We'll fix your Subaru (old or new) and get it running smoothly and efficiently once again.

Schedule service at Hanson Subaru in Olympia, WA
Order parts online at Hanson Subaru

Hanson Subaru

2300 Carriage Loop SW
Directions Olympia, WA 98502

  • Call or Text Sales: 360-943-2120
  • Service: 360-943-2121
  • Parts: 360-943-8531
  1. Hanson Subaru

    2300 Carriage Loop SW
    Olympia, WA 98502

    • Sales : (888) 490-9863

Map Data
Map data ©2018 Google
Map DataMap data ©2018 Google
Map data ©2018 Google