Car Engine Misfires: What Reasons To Anticipate?

Engine misfiring can happen when one or more of the cylinders do not supply power to the car.

Engine misfiring can happen when one or more of the cylinders do not supply power to the car.

The problem could be as simple as failure of the spark plugs or ignition wire or a complicated one related to fuel system or internal engine defect. The longer the problem is neglected the severe damage it can cause to the vehicle. It is very important to timely address this issue to ensure vehicle safety, longevity and fuel economy. Otherwise, the problem can worsen over time and lead to very expensive repairs damaging important internal parts of the engine.

Symptoms Of Engine Misfiring

When suspecting engine misfiring, it is better to watch for these symptoms while driving. The symptoms vary based on the reason that is causing the engine to misfire. When it is fuel system issue, the symptoms may suddenly appear and are often noticeable. The engine idles accompanied by a loud noise, smell or smoke from the fuel exhaust. Misfiring of engine can also result in loss of power causing sudden failure or slowing down of engine while accelerating from idle. The gas mileage will drop and the vehicle can even fail emissions. It is not easy to identify the exact cause because it can be caused by a number of different reasons. Sometimes, the problem could be serious enough to cause noticeable vibration or backfiring but the symptoms are not always the same. A code reader can be connected to the Engine controlled Unit (ECU) which will provide the engine fault codes of possible issues. These error codes will only help to narrow down the issue but cannot identify the part that is causing the problem.

The Reasons That Can Cause Misfiring Symptoms

  • Faulty Spark plug, bad plug wires or ignition coil
  • Clogged fuel filters or dirty fuel injectors
  • Faulty fuel pump or airflow sensor
  • Low fuel pressure
  • Damaged manifold gasket, cracked head or damaged rings
  • Slipped timing belt or chain

How To Resolve Misfiring Problems?

To diagnose the issue it is better to follow a step by step process such as checking the vehicle first for simple issues and then navigating to the complex problems. You can use a scan tool to read the error codes by plugging it to the vehicle's diagnostic connector located under the dash board. However, the scan tool can display which cylinder or cylinders are misfiring but do not tell the reason that is causing the cylinders to misfire. Once the misfiring cylinder is isolated, it requires thorough diagnosis to identify whether it is ignition, compression or fuel related problem. First the vehicle needs to be checked for faulty spark plugs, plug wires or broken ignition coil. If it is a mild issue it will not trigger an error code in the code reader. In such cases the LTFT (Long Term Fuel Trim) reading will help you quickly diagnose the issue and alert you to future problems. Also check for fuel pressure to see if the pump is weak or the pressure regulator is defective. If the pressure is within specification, check for vacuum lines and the intake manifold gasket for any faulty parts. If no issue is identified, take a look at timing belt and valve train for any obvious damages. Perform a compression test to determine if the problem is compression related. If you are too confused pinpointing the defective part, it is better to take your vehicle to a trained automotive technician who has hands on experience repairing misfire problems. is a website from US Motor Works (USMW), manufacturer of electric fuel pumps, fan clutches, automotive water pumps, oil pumps, cooling accessories and other automotive & heavy duty engine parts. Fuelpumpu is designed specifically to provide information on fuel delivery systems including fuel pump installation, technical tips, fuel pump problems, diagnostic procedures, fuel delivery issues, fuel pump repair and more. For further details, please visit

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