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An engine misfire happens when a cylinder doesn’t combust fuel. It often stems from relatively minor issues like worn spark/glow plugs or dirty injectors, but the real danger comes from leaving the problem unchecked.
Misfiring engines can send unburned fuel into the exhaust system and the cat (catalytic converter). They can also introduce more heat to the engine as good cylinders compensate for bad ones, accelerating wear in the valves and cylinder heads – and all these are more expensive to fix than the average misfire.
The smart play is to act quickly at the first signs of engine misfire - use your instincts and those check engine lights as a friendly warning system for your vehicle. Then, let a mechanic diagnose the root cause – which might just be some bad spark plugs.
How Misfires Happen
A perfectly timed combustion ballet occurs within each engine cylinder to generate power. When the piston reaches the top of its movement, the spark plug must fire to ignite the air-fuel mixture at just the right moment. This explosion drives the piston down, allowing the process to repeat. If anything interrupts this delicate sequence, that cylinder can misfire.
Noticing the Signs
The first step is identifying that you have an engine misfire.
There are some clear symptoms to look out for:
- Loss of power under acceleration.
- Jerky acceleration.
- Rough, uneven idle.
- Vibrations or shaking sensations.
- Flashing or intermittent check engine light.
- The easiest way to tell is if the engine momentarily stumbles.
If you notice these symptoms, it's quite likely your engine is misfiring. The check engine light is especially telling - this typically activates misfire detection codes that can help narrow down the cylinder(s) affected. Getting the codes read at a repair garage is highly recommended, as it provides a starting point for diagnosing the root cause.
Note that some things are mistaken for an engine fire. Engine knock/pinging is the main one – when fuel combusts unevenly in the cylinder, creating a knocking sound, this is often confused with a misfire. However, a knock happens when the cylinder fires, while a misfire is a failure to fire correctly.
Potential Causes
Several components in the ignition and fuel delivery systems could cause a misfire when they fail:
- Faulty spark or glow plugs - These may be worn and fouled after high mileage use. Issues like improper gapping or carbon buildup prevent complete plug firing.
- Defective ignition coils - These generate the high voltage for the spark plugs. If damaged or faulty, they cannot correctly ignite the mixture.
- Vacuum leaks - Small leaks throw off the engine computer's air/fuel mixture calculations, resulting in incomplete combustion.
- Damaged wiring - Crack or worn spark plug wires cause ignition performance issues, translating to misfire events.
- Sensor issues - Sensors provide essential data to the computer to synchronise the ignition and fuel systems properly. Faults lead to mistiming and misfires.
High-mileage cars are more likely to experience engine misfires, so if you rack up the miles, pay special attention to any vibrations and juddering.
Repairing the Root Cause
An engine misfire can sometimes be caused by multiple faulty components rather than just one issue. Replacing parts without fully understanding the root cause wastes money and time. An experienced technician will methodically track down the source using diagnostic approaches such as:
- Code readers plugged into the onboard computer to access and decipher any logged check engine codes.
- Compression testing checks engine compression readings cylinder-by-cylinder to pinpoint low values indicating leaks or ring/valve damage.
- Waveform analysis uses an engine oscilloscope to see ignition voltages and patterns visually. Technicians can analyse the waveforms for faults pointing to specific ignition components.
- Fuel injector testing confirms whether injectors deliver the proper fuel pressure and spray patterns. Any degradation can signal damaged injectors needing repair.
For example, finding a vacuum leak as the culprit means searching for cracks in hoses, bad gaskets, or loose fittings. An ignition coil giving a weak spark may get replaced, while cleaning dirty fuel injectors could be the fix instead of replacement.
Getting to the core problem takes automotive experience and diagnostic due diligence. Remember - no mechanic should swap parts without understanding what's making the cylinder misfire. Doing so is a recipe for huge repair bills.
Homing in on the faulty component also prevents replacing several good parts needlessly. An expert technician will zero in on the root cause to create a fix.
Should You Continue to Drive?
DO NOT continue driving with a suspected engine misfire, even when the problem is intermittent. Ongoing operation with misfiring cylinders risks further damage and hefty repair bills. Here's how:
- Catalytic converter damage: Unburned fuel and raw emissions pass through to poison and overheat the catalytic converter - requiring an expensive replacement.
- Additional misfiring cylinders: Other cylinders can begin misfiring from being forced to compensate for the failing one(s).
- Piston and cylinder head erosion: Lack of ignition relieves pressure, allowing air/fuel mixture to eat away at critical engine components through uncontrolled combustion.
- Burnt valve pistons: Flame from backfires in the intake can shoot into engine cylinders and scorch internal structures like valves and piston tops.
- Engine overheating: Misfires hinder oil circulation flow, leading to possible warpages or cracks in cylinder heads and blocks.
The Next Steps
Ignoring engine misfires risks further damage to your engine and overall performance. The best move is to have your vehicle inspected and repaired by us as soon as any symptoms appear. We have the skills and diagnostic capabilities to get your engine running right again. Expect a full inspection, trouble code readout and necessary repairs.
In many cases, the fix involves affordable parts and uncomplicated replacement. Feel free to get in touch for more information.