Quick engine misfire check engine light tips!
There are 2 general types of engine misfiring: random misfire and a specific cylinder misfire. On the first case, it is shown by a P0300 fault code whereas the cylinder misfire is designated by a code number like P0301, P0302, P0303, P0304,etc where the last digit denotes the specific cylinder where misfiring occurred. So if you have a misfiring fault code like P0303, it means the misfiring happened in cylinder number 3.
Diagnosing random misfire code:
This fault code is usually cause by a problem common to the engine: vacuum leak which can cause a lean fuel mixture, bad or defective fuel pump will also cause lean mixture including a defective or weak ignition like poor spark or low combustion due to worn cylinder, bad shorted wirings and defective sensor can also cause random misfiring. The trick in fixing this random fault code is finding the common culprit causing the misfire.
Here below are few examples:
Vacuum leak:
Check for vacuum leak: listen for hissing sound on vacuum hoses, spray mist of water on suspected vacuum leak at idle and rpm should change, do the same spray on suspected intake manifold gasket, a cracked vacuum hose can also do this misfiring for you. Out of time timing belt can reduce vacuum reading and cause random misfire.
Weak ignition:
Check the quality of the spark by checking the spark color and strength, check also if the spark is continuous. Weak ignition can be traced to defective ignition coil, spark plugs and wires and sometimes even a defective crank sensor and ignition module.
Poor fuel supply:
Measure fuel pressure reading using a fuel pressure gage and compare them to the standard specs. Clogged dirty fuel filter can also cause restricted fuel supply causing misfiring.
Shorted wiring or defective sensor:
When a wiring happens to be shorted, it can disturb the sensor signal to the computer and this can be verified by doing simple wiggling of the wires and it could reveal the culprit wire or circuit. Poor ground connection can also make electronic parts useless. On some sensor like the load sensors namely the tps or mass sensor, any defect on them can trigger random misfire under load.
Diagnosing cylinder misfire code:
This misfiring is best tested by checking the cylinder mechanical condition by testing the integrity of compression, fuel injector, spark on the specific cylinder and compare it with the cylinder that is working. One popular technique used by some mechanics is to switch the defective spark plug or ignition coil or coil plug to a good one and see if the code will also move. Example, if after you switch the cylinder #1 coil plug to cylinder#4 and after testing the fault code changed from P0301 to P0304, you know that the coil plug is the defective. This switching can also be done on suspected injectors, plug wires, ignition coil, etc. as long as the cylinder causing the misfire is identified.
Tip:
On some engine code scanners, a freeze frame data can be seen live on the exact condition of the engine. This can save you time in analyzing the defect of the cylinder.
