Wednesday, 8 April 2015

Engine Misfires Or Runs Rough

Misfire - Engine Miss

My Car Engine Misfires while starting or running
Vehicle Runs Rough

Helpful Information
An engine tune up is necessary at manufacturers recommended intervals to maintain proper engine run-ability. A misfiring engine will cause, low gas mileage, low power output, increased emissions and possible internal engine damage if left untreated. Typically an engine misfire under load, will be a problem with the ignition system, while low engine speed problems will be a vacuum, fuel management or compression issue.
When retrieving trouble codes, only consider related codes to a specific misfire problem, like an ignition coil failure code. If a trouble code is present and doesn't pertain to the immediate problem like an EVAP code, ignore it until a later time, when the engine is  running properly these codes could cycle out.

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, quicklytake 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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