Engine Misfire Auto Repair

An engine misfire is a failure of one or more cylinder causing engine to run erratic. The misfire can be caused by many factors such as poor maintenance. An efficient engine will keep running for over 200,000 miles with proper care. Lack of proper care can prematurely shorten an engine’s life and can be costly to repair.


A tip to avoid costly repair is to have tires properly inflated. Another tip is to change engine oil at the recommended service time. For example, engine oil should be changed ever 3,000 miles or every 3 months.

Cause of a misfire

The cause of a misfire is when air/fuel is unable to ignite on the compression stroke. A cylinder or more can fail and not produce the desire power. One of the problems is a failed combustion chamber. Normally one or more cylinders miss under idle, under acceleration or cruising speed. The problem can happen when the fuel mixture fails to ignite and burn properly under such condition.

What to look for when an engine misfire

In a multiport fuel injection, an injector may not open properly. Make sure all the injectors are functioning properly. Conduct a test and check each injector for its function. An injector should be able to spray fuel in a clean fashion and not drip.

A fouled spark plug can fail to spark. When it fails to spark, the air/fuel mixture is unable to ignite therefore causing that one or more cylinder to misfire. Check all spark plug condition, if possible replace all the spark plugs with new one.

A bad spark plug wire. A bad spark plug wire will fail to deliver power to the spark plug. Check all wires with an multimeter and set to ohm. The resistance value should be in range according to manufacturer specification.

A low compression can also contribute to misfire. Air/fuel must be under pressure to fire properly to combust. A low compression can be check by performing a compression test. All cylinder must have similar reading. If one of the reading is lower than the other, it is possible the piston ring is bad. Also, a bad head gasket can contribute to a misfire.

A worn/crack distributor cap and vacuum leaks are a few other possible causes.

Using a scan tool to locate the problem

A scan tool can help locate the problem of a misfire and make life much easier. It is able to pinpoint the problem as soon a scan tool is connected to the data link connector. Once the scan tool is connected to a data link connector, a code can be read. An example reading of an engine misfire: P0301 “Cylinder 1 Misfire Detected” or p0313 “Misfire detected low fuel level.” Here is a simple scan tool costing below $100 and can get most job done.

Before taking your car to the mechanic

You must first get your hands dirty. By performing basic check, you can save hundreds of dollars. If somehow, you are unable to diagnose the vehicle yourself, take the vehicle to a reputable auto shop. Call around and ask for a price quote and get an opinion. This way, you can compare each auto shop advice and price.