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How to Check for Sparks Using a Timing Light

Updated July 20, 2017

Misfiring spark plugs or bad induction wires are common reasons for poor engine performance. An old practice was to pull off a plug wire while the engine was running to see whether it sparked to ground. Usually, the one pulling the wire off became the ground, resulting in a sudden set of shocks to the body and a newfound respect for the ignition system. An easier way to to check a plug and wire is to use an induction timing light.

Examine the inducton timing light. Notice that there are two coloured leads with wire clamps. These hook up to the battery -- red to the positive battery terminal, and black to ground. Look closely at the induction pickup end. It will have a large black plastic clap that surrounds the plug wire being checked. Most induction pickup ends will also have an embossed arrow that indicates the voltage flow through the wire. Hook it up accordingly.

Start the car and return to the engine compartment. Pull the trigger on the timing light and observe what appears to be a strobe light. As that particular spark plug fires, the strobe also lights. Look for consistency in the blinking of the light at different engine speeds. There should be a regular strobe action throughout all speed ranges.

Move the induction pickup to each of the other plug wires. Shutting off the engine while moving the pickup is not necessary. Observe the results of each test as the pickup is moved from one wire to the next and record any discrepancies.

Review your notes and look for the plug wires that were inconsistent in the strobe or had no lighting at all. These are the plugs or plug wires that need further testing.

Tip

Wearing heavy gloves will help alleviate the plug wire jitters. Write down the test results for each cylinder. It will be easier than trying to remember after all wires are tested.

Warning

Hook up the induction pickup coil with care. Leaking plug wires can still shock exposed skin.

Things You'll Need

  • Induction timing light
  • Pencil
  • Paper
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About the Author

Curt Von Fange, an ASE Master Automotive Technician, began writing in 1998. His first article related a memorable experience about panning for gold with his father. It was published by "Gold Prospector Magazine" the following year. An associate degree in heavy equipment repair from Ferris State College helps him write numerous technical articles for trade magazines and webzines like YTtractors.com and Desertusa.com.