Inline Spark plug And Spark plug Wire Testers: What Are They And Do You Need Them

Electrical problems can be some of the most difficult problems to troubleshoot and repair without the proper test equipment. Two such test instruments that every shade tree mechanic needs to have in his or her tool kit are an inline spark plug tester and spark plug wire tester. Like I pointed out in my article on Battery Keepers, most of these gadgets are so inexpensive that every shade tree mechanic can have a couple of them in his or her tool kit. The two that I am going to discuss in this article can be ha for less than $25 online.

The Inline Spark Tester
The in line spark tester is an essential gadget because using one is the only safe way to check for spark at a spark plug in today’s cars. The old-time method of simply holding the spark plug wires 1/8 to ¼ inches from the engine can cause damage to the ignition systems electronic components. The arc caused by that method set up an extremely high surge current that the electronics cannot handle safely. Many shade tree mechanics make their own in line testers using an old spark plug with a large alligator clip welded to it. You can buy a better one for $10 to $15. The commercial ones tell you if there is a spark. They also give you a visual indication of what the spark is like inside the combustion chamber. Having one of these gadgets in your mechanics arsenal is the next best thing to having an O-Scope.

The Spark Plug Wire Tester
The High-Energy Ignition (HEI) systems in today’s car produce 30,000 volts or more and place a lot of stress on the secondary wiring. Unlike with the old 10,000-volt breaker point systems, leakage is much more of a problem. Tracking down secondary ignition current leakage can be a challenge without an O-Scope or this $10 spark plug wire tester. Clip the ground wire to any good ground and run the probe along the high-tension wire. Leakage current will cause the probe to glow. Although not designed for the purpose, this probe will detect leakage through the towers on the distributor cap.

For the new do-it-yourself, the basic tools are often better that, the expensive professional tools. That is especially true for test equipment. Sooner or later you will want to add an O-Scope to test equipment arsenal but learning to interpret the traces displayed on an O-Scope screen takes time, lots of time. An O-Scope has a steep learning curve whereas the in line spark tester and the spark plug wire tester has no learning curve at all. If your budget permits, buy an O-Scope too. Once you have mastered using it, you will find it indispensable or troubleshooting the on board computer and its related sensors.