What Makes an engine backfire? | Ontario Chrysler Service

You might associate backfiring cars with older vehicles, or clown cars at the circus, but backfiring is actually a helpful signal that your car of whatever age needs some TLC.  When a spark plug, or multiple spark plugs, ignite the fuel in their cylinder out of turn, it causes a delayed detonation. Here are some likely causes.

Too Rich Fuel Mix

If your car’s engine is being fed more fuel than it needs to burn efficiently, you’ll get what’s called a too-rich fuel to air mixture. It might be time to change your dirty air filter, a simple fix. If the engine is running too rich, an excess of fuel slows down the efficiency of the flame. When the fuel burns slow, the cycle isn’t completed before the exhaust portion of the engine cycle happens. The exhaust valve opens on that slowed-down cylinder, and the extra air allows the unburned fuel to burn explosively, creating the pop or banging sound. 

Timing is Off

Better known as retarded timing, delayed timing can also cause a backfire. The engine cycle of fuel-compression-ignition-exhaust in the cylinder head isn’t in proper sync with the cylinder block at the bottom end. The ignition cycle begins too late in the combustion chamber and ignites the fuel right as the exhaust valve is opening.

Distributor Cap Issues

Some cars don’t have ignition coils on the spark plugs. Instead, a distributor cap and wire set disperse the electrical pulse to the spark plugs. This pulsing action causes the spark plug to spark and ignite the fuel in its cylinder. If your distributor cap is cracked, moisture may get in and cause the spark from one cylinder to track over to another, incorrect cylinder. A backfire results when that incorrect cylinder fires out of time as the exhaust valve opens. If you happen to have a car with a distributor cap, make the replacement of it a part of your regular tune-up. We encourage preventative maintenance as a way to take great care of your vehicle. 

 

Carbon tracking can come into play in more than one scenario. Again, if your vehicle’s design involves a distributor cap, the spark plug wires are all attached to the top of the cap. Environmental elements can, as time passes, cause the spark to cross over from one spark plug wire to another. If the proximity of the plugs is too close, the frequent sparking can cause a carbon track to form. The misfire that results is much like that of a cracked distributor cap.

If your spark plug wires or ignition coils are mounted right onto the spark plug, carbon tracking can also form. If part of the spark takes an incorrect path, and the remaining spark isn’t intense enough to ignite the fuel, it leaves some carbon in the cylinder. Now, the next ignition may be sufficient to fire the spark plug, this time carrying that extra fuel in the cylinder. If that burn cycle isn’t explosive enough and doesn’t complete before the exhaust valve opens, you’ll hear a backfire when it does.

Keep in mind that backfire situations almost always come with other symptoms attached, such as seeing your Check Engine light illuminated. When your car backfires, it’s a clear signal that your vehicle isn’t running efficiently.

Contact us at our Ontario Chrysler service centre so we can help you attend to that issue promptly. Ontario Chrysler's Service Departments, located in Toronto and Mississauga use advanced service technology that will save you time and money. Learn more here.