Depends on the type of problem you're trying to solve. If you're working on a crank / no-start, you know all the coils won't fail at once, so there's no point in testing them. If you have a diagnostic fault code for a single-cylinder misfire, lets say cylinder number two, for example, the best approach is to switch coil number two with coil number three, and injector number two with injector number one. Erase the fault code, then, when it comes back, if the code specifies a misfire on cylinder number three, it's due to the ignition coil. If the misfire moves to cylinder number one, it's due to the injector. If the code keeps returning for cylinder number two, the better suspects are low compression, a burned valve, wiped out camshaft lobe, or something else related to that cylinder.
If you know an ignition coil is causing a problem and you solve it by replacing it, there's no point in testing the failed part other than to learn why that failure occurred. Start with continuity tests between all of the terminals. Approximate normal values are given in service manuals, but those are just for reference and training purposes. On the job, we don't care about the actual values we measure. It's "do we have something or nothing", so to speak. The wire for the primary coil is rather tough, so failures are rare. The secondary wire is very fine and long, so if there's going to be a break in a wire, that's the one to expect to find. Even those don't break very often.
The reason we never waste our customers' time testing parts this way is electrically, everything can be okay, but if internal carbon-tracking has developed, that can short out the spark that's being developed. Most of the time that carbon is too high in resistance to be measured, plus, it develops between terminals that are already connected with wires. If you rely solely on continuity tests, you'll overlook the problem-causing part. Better is to switch two, then see if the problem moves to a different cylinder.
Thursday, May 15th, 2025 AT 9:33 AM
