How to Identify Which Cylinder is Misfiring in an Engine

[LaCaroline]

Here are the relevant methods to determine which cylinder is misfiring in an engine: 1. Cylinder Cut-off Method: You can use the RPM fluctuation of an electronically fuel-injected engine to identify the misfiring cylinder. First, disconnect the high-tension wires of each cylinder one by one. If the tachometer shows significant fluctuation when a wire is disconnected, it indicates that the cylinder is functioning properly. If there is no fluctuation in the tachometer after disconnection, it means that cylinder is misfiring. Further inspection of the ignition coil and spark plug of that cylinder is required. 2. Fuel Cut-off Method: Primarily used for diesel engines, but can also be applied to electronically fuel-injected engines. You can disconnect the fuel injector connectors one by one to check for misfiring. For gasoline electronically fuel-injected engines, the RPM fluctuation can similarly be used to determine misfiring. Diesel engines provide a more direct observation—when the injector of a normal cylinder is disconnected, the engine RPM will continuously drop. If the injector of a faulty cylinder is disconnected, the RPM will not drop.

[Reyes]

I've encountered this issue before, where the engine was shaking like it was dancing. You can place a screwdriver against your ear and listen - the vibration sounds from each cylinder should be fairly even. If one cylinder sounds particularly weak, there's likely a problem. The most accurate method is to disconnect the ignition coil connectors one by one: first unplug one, listen for changes in the engine sound. If there's little change, it means that cylinder was already slacking off and not working. Then move on to the next one and continue testing. Be careful not to get burned during the operation, as the engine runs hot. I've tried this method myself twice before, and eventually found out the second cylinder was misfiring. Replacing the spark plug fixed it.