Here is the scenario: You are travelling on the highway, travelling long distance to ur hometown. Suddenly, ur engine becomes sluggish and power is lost, and u know its misfiring. Most of the time, the ignition coil is the culprit. U stop at the nearest lay-by/R&R to troubleshoot the issue as u hv a spare ignition coil in the trunk (perhaps a spare etc.). Problem is, u dont hv those handy INPA/scanner or any other device that can help u diagnose or help u determine which coil/cylinder is giving u that issue. Question: How do u determine which coil at fault? U do not have any assistance and u need to change it to get underway.