It is important to check for the presence of spark to all of the cylinders to isolate the problem to either EI system ignition coil inputs or outputs. In checking the ECM outputs for the electronic spark timing signal, it is recommended to use an oscilloscope to view the varying voltage signals. In measuring these outputs with a voltmeter, intermittent errors may occur that cannot be seen by a voltmeter.
After confirming ECM inputs for the electronic spark timing to the EI system ignition coil are OK, it can be determined that a faulty EI system ignition coil is at fault. After confirming proper CKP inputs to the ECM and no wiring problems present, it can be determined that the ECM is at fault.
Check for battery voltage and a ground to the EI system ignition coil. If the wiring between the EI system ignition coil and the battery positive is OK, the problem is in the ignition relay circuit.