An ignition coil can be OHM checked with a meter to see if it is out of range or if it has a completely open circuit. But what if the car sees to run fine and a misfire code is directing you to a particular cylinder? For instance if you have a code for * P0301 (# 1 misfire code) but the engine looks to be running OK, below is a low tech method for testing the coil without any special tools. This method works well for ignition coils or fuel injectors that may have an intermittent problem. Also it works best with ignition coils and injectors that are easily accessible. Obviously it's best to check the basics first like a visual inspection to see if engine oil may be shorting a connection or if there is evidence of tracking the spark arcing to the engine. Sometimes after an engine is cleaned water can go into the spark plug recess and short the connection to the plug as well. The simple low tech method is assuming the spark plugs and wires are good and there is still a misfire code setting.
What is the low tech method?
Simple, switch the coil or injector with the neighboring one. After making the switch clear the code and see if the misfire code sets for the other cylinder. Sometimes in service manuals, you may read "install a known good component." This is basically what is being done without the expense of purchasing a new part for testing purposes. Usually with electronic parts, stores will not allow returns. This way no unneeded parts will be purchased.
- Save money by using this simple low tech diagnostics method.
- Pinpoint intermittent problems with ignition coils or fuel injectors.
- Use this method without intensive knowledge of the ignition or FI systems.
- Perfect DIY test to verify a failing component without spending money or guessing.
- By switching cylinder # 1 and # 2 coils the code should move from * P0301 to P0302 if the coil is bad.
- Eliminate the possibility of bad wiring or a computer driver issue.