Mechanics

Misfire - Engine Miss

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Step by step guide on how to troubleshoot and repair an automotive engine cylinder misfire, this information pertains to most non electric vehicles.

Difficulty Scale: 4 of 10

Begin with the vehicle on level ground engine "OFF" and the parking brake set, wear protective gloves and clothing for safety.

Step 1 - There are several combinations of misfire conditions, steady or random, at idle or under power, which may or may not be detected by the computer and trigger a check engine or service engine soon light, read trouble codes to help pinpoint the cylinder(s) in question and follow the repair guide below.


Check Engine Light

Step 2 - If no service light is triggered with a steady misfire, use an infrared thermo gun to test the exhaust temperature of each cylinder.


Infrared Temperature Meter

Step 3 - Start the engine cold, quickly take a reading at the front of each cylinder's exhaust port on the manifold while maintaining similar placement of the beam over each individual port, a misfiring cylinder will be considerably colder than the remaining cylinders. Example: Three of the exhaust ports test at 190 degrees while one is at 81 degrees, the cylinder at 81 degrees is misfiring.


Exhaust Temperature

Step 4 - If no results are yet gleaned, start the engine and allow to idle, remove the fuel injector electrical connector on each cylinder one at a time while observing the engine performance, if no change is observed at a particular cylinder, the misfiring cylinder has been located.


Fuel Injector Wire Removed

Step 5 - This can also be achieved by removing a coil wire connector (COP systems only - no plug wire attached ).


Remove Ignition Coil Connector

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AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2014-08-04)