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Diagnostic Center

What Should I do If My Engine Misfires?

Problem

Nothing gets your attention like an unexpected change in the performance of your vehicle’s engine. A misfire will cause the engine to momentarily stumble, or lose rpms, and then regain its normal engine speed. The misfire will usually reappear, either under specific operating conditions or randomly. A misfire may occur when your engine is idling, causing a rough or uneven idle.

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Causes

A misfire usually starts out as being merely a nuisance but if the causes aren’t identified and corrected, it may result in your engine not starting or stopping altogether when you least expect it. Many system malfunctions can cause misfires or rough idling. 

Ignition system components, including spark plugs, plug wires, ignition coils and ignition timing are culprits as are lean air/fuel mixtures and mechanical issues within the engine. Worn piston rings, worn or broken valves and worn cylinder walls, as well as worn cam lobes can also contribute to the problem.

Symptoms

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Sluggish or rough acceleration

When the engine misfires, you may have trouble getting your vehicle up to speed. Misfires often happen when your vehicle is under load while accelerating. This can result in slow or sluggish acceleration or a jerking motion while pressing down on the accelerator.

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Rough idle

A rough or uneven idle can be an indicator of an engine that is misfiring. The air/fuel mixture is disrupted which can cause the engine to jump up and down. 

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Illuminated check engine light

Modern vehicles have many sensors that monitor the vehicle’s performance. If a sensor detects a problem with the engine, it sends the information to the engine control unit. If the problem is deemed serious, the Check Engine light will illuminate, alerting you to a problem that needs attention.

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Changes in engine sound

If your engine is misfiring, you’ll likely hear it. Turn the radio off and listen closely to your engine. Does it sound different than normal? Unusual sounds can be a clue that there is something going on with your engine. 

Solutions

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If you’re experiencing a misfiring engine, you’re likely going to need to enlist the services of your mechanic. Before you take your vehicle to the shop, gather as much information as possible to assist your mechanic in diagnosing the problem. 

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While driving, pay close attention to how your engine is running. When a misfire occurs, take note of the circumstances such as whether the engine is cold or has warmed up; the speed at which it occurs (low speed or high speed); the frequency it occurs; and if it occurs only when accelerating or at a steady speed. Keep a log of the problems, this information will help your mechanic pinpoint the source of the problem.

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Visually inspect the engine area of your vehicle. With the vehicle shutdown and cooled off, look around to see if anything strikes you as being wrong, such as obviously loose or unconnected wires, broken parts, fluid leakage or anything else that looks out of place.

Armed with this information, your mechanic will have your vehicle hitting on all cylinders and running smooth in no time.

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The content contained in this article is for informational purposes only and should not be used in lieu of seeking professional advice from a certified technician or mechanic. We encourage you to consult with a certified technician or mechanic if you have specific questions or concerns relating to any of the topics covered herein. Under no circumstances will we be liable for any loss or damage caused by your reliance on any content.

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