When overhauling a fire fault, use high voltage line to check cylinder body. If there is no fire, it means that corresponding ignition coil and its control part are not working properly.
The method for troubleshooting a spark plug without igniting engine is as follows:
First check if high voltage line is good, then check if ignition signal control circuit is good. If circuit is good and there is no high voltage on secondary side of ignition coil, an oscilloscope can be used to locate ignition control signal between electronic controller, ignition electronics, and ignition coil. If signal is normal, it is basically a fault in ignition coil circuit.
Take checking 1st and 6th cylinders of an inline 6 engine as an example, check out troubleshooting steps and methods for flashing ignition system and the fire engine not working.
Steps and Troubleshooting for Ignition Flashing and Fire Engine Not Working