Cylinder misfires

A cylinder misfire can be identified by the Check Engine Light on or blinking and the engine running rough. The cylinder misfire can make the engine feel like it is skipping with lack of power.

When the Check Engine light is “blinking” this is the universal sign for “P0300-Random Cylinder Misfire”. If you have obtained the p-codes and have anything between P0301 – P0308, these are cylinder misfire codes for a specific cylinder respectively. There are a few different things that can cause a cylinder misfire.

First we’ll need to inspect the plug and check for spark. Remove the spark plug and inspect it for any cracks. Inspect the diode and make sure it’s not excessively worn or broken. If there are any doubts, replace the plugs (it is recommended that all the plugs be replaced at the same time!). If the plugs look good, next use an In-line ignition spark tester between the ignition coil (if equppied) or spark plug wire (if equipped) and the spark plug. Crank the engine. If the tester is not blinking, there is loss of spark. If this is the case, check your distributor cap and rotor (if equipped) or ignition coil (if equipped) and replace as needed.

If the spark checks good, the next step is to check the Fuel Injector and injector pulse. Using a Noid light set, unplug the electrical connector to the injector and install the noid light into the plug. Crank the engine. If the noid light is not blinking, there is loss of injector pulse. If the pulse is good, move onto the injector itself. If you have access to a multimeter that can test for resistance (ohms) you can unplug the electrical connector to the injector and take a reading across the two blades on the injector. If the ohms value does not match the OE specs, replace the injector. If the ohms value is correct there is a chance the injector is still semi-clogged. With the engine running, unplug the electrical connector to the fuel injector. If the engine doesn’t respond (it should get a little more “shaky”) the injector will need to be replaced.

If both spark and fuel test good, next we’ll need to do a cylinder compression check. Remove all the spark plugs. Disable spark. Disable fuel. Then, using a cylinder compression tester, test each of the cylinders compression. If the cylinder compression does not meet OE specs, there is internal damage and some further inspection will need to be done.

If the compression check ok, next check for any air leaks around the effected cylinders. With the engine running, carefully and sparingly, spray some Throttle Body Cleaner around the base of the intake. If the engine responds (usually a jump in RPM or the skip smooths out), this is a sign of an air leak from the intake gasket. The intake should be visually inspected for any cracks and the gasket will need to be replaced.

If all of these check ok, then some deeper diagnostics will need to be done to determine the root of the problem. But these are the “basics” to finding the cause of a misfire and more times than not, one of these will solve the problem.

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