How to Test an Ignition Coil for Vehicles

by Contributing Writer

Before solid state ignition systems and computerized engine management systems, checking ignition coil output was simply a matter holding the coil wire near the engine block while you cranked the engine over. The color of the Vehicles as well as the length of the Vehicles was a good indication of the condition of the ignition coil. This method of checking Vehicles can cause irreparable damage to modern solid state ignitions systems and computerized engine management systems because of the resulting surge of high voltage current. You can buy a special tester that allows you to view the Vehicles safely, or you can make your own from a Vehicles a fraction of what the tool would cost you.

Under The Hood:

 How to Test an Ignition Coil for a Yamaha YFM 80

Park the ATV on a level work area. Remove the seat from the ATV, using the release lever under the rear of the seat.

Remove the front panel or grill from the front fender, using a ratchet. Remove the front fender mounting bolts, using a ratchet. Lift the fender off of the ATV. Unscrew the ignition switch lock nut from the right side of the front fender by hand, then push the ignition switch out of the fender.

Turn the fuel valve, located under the bottom-left corner of the fuel tank, to the "off" position. Unscrew the fuel tank mounting bolts using a ratchet. Lift the tank off of the ATV and pull the fuel hose off of the fuel valve outlet using pliers.

Grasp the spark plug cable cap, located on the left side of the engine cylinder, then pull the spark plug cable off of the spark plug. Follow the spark plug cable to the ignition coil, located along the ATV's frame rail. Unbolt the ignition coil, using a ratchet, then unplug the coil from the ATV's wiring harness.

Pull the cap off of the spark plug cable. Set a multimeter to a 1x resistance setting. Place the meter's red probe into the cap's spark plug receptacle and the black probe into the cable-end of the cap. The meter should indicate a resistance reading of 10k Ohms. Replace the spark plug cap if the resistance is greater than 10k Ohms.

Move the red probe to the ignition coil's wiring terminal and the black probe to the ignition coil's body. The meter should indicate a resistance reading of 1.4 to 1.8 Ohms. Replace the ignition coil if the resistance reading is greater than 1.8 Ohms.

Move the red probe to the ignition coil body and the black probe to the end of the spark plug cable. The meter should indicate a resistance reading of 5.3 to 7.9k Ohms. Replace the ignition coil if the resistance reading is greater than 7.9k Ohms.

Push the spark plug cable cap onto the end of the spark plug cable. Reinstall the ignition coil onto the ATV's frame. Push the spark plug cable cap onto the spark plug.

Reinstall the fuel tank onto the ATV, then push the fuel hose onto the fuel valve outlet. Reinstall the front fender, front grill and seat.

Items you will need

  • Ratchet

  • Socket set

  • Multimeter

 How to Test the Ignition Coil on a Chevrolet

Test for power and ground at the coil during cranking. If power is found on one side of the electrical connector on the coil during cranking, and flashing ground is found on the other side, this indicates an open coil. Replace the coil to repair. If power is present on both sides of the electrical connector, the coil primary winding is not open, but may be shorted. If no power is present at the coil electrical connector, check for blown fuses, or burned fusible links. The locations of these can be found in the service manual for your specific Chevy vehicle.

Remove the coil electrical connector and the coil wire. Attach the test leads from the digital volt/ohm meter to the pins in the coil where the electrical connector attaches to test the primary winding for resistance. Set the meter for ohms and compare the reading on the meter to the factory specifications in the service manual. Resistance specifications vary, so consult the service manual for the specifications for your specific vehicle. Replace the coil if the resistance is out of the range of the specifications.

Test the secondary for resistance by attaching the leads from the meter to the coil wire connector on the coil and the metal body of the coil. Any resistance reading during this test indicates a shorted coil. Replace the coil if the resistance during this test shows anything but an open circuit.

Items you will need

  • Automotive circuit tester

  • Digital volt/ohm meter

  • Service manual

 How to Test the Ignition Coil on a Dodge Dakota

Use a can of compressed air to blow away any dirt and debris around the ignition coil, especially around the coil's base.

Remove the ignition coil from the engine by disconnecting its electrical connector, removing the coil's mounting nut and detaching the coil from the spark plug.

Clean off any corrosion from the coil tower terminal with a wire brush.

Connect the leads of an ohmmeter to both primary terminals of the coil and measure the primary resistance. The resistance needs to be between 0.6 and 0.9 ohms.

Test the secondary resistance by connecting one ohmmeter lead to the positive terminal and the other lead to the high tension terminal. The secondary resistance needs to be between 6,000 and 9,000 ohms.

Items you will need

  • Compressed air

  • Wire brush

  • Wrench

  • Ohmmeter

 How to Check the Ignition Coil on a 1995 Civic

Open the hood of the Civic and set the hood prop. Mark the wires on the distributor cap by wrapping masking tape around the wires. Number the wires from 1 through 4, corresponding with the numbers that are stamped into the distributor cap. Remove the spark plug wires from the ignition coil by twisting them slightly while pulling them off the coil.

Remove the mounting screws for the distributor cap with a Philips screwdriver. Remove the distributor cap from the engine, as well as the rubber gasket between the cap and the distributor body. Remove the two screws that hold the wires down to terminals A and B, then remove the black-and-yellow wire from terminal A, and the white-and-blue wire from terminal B.

Turn the selector on your multimeter to the Ohms selection, or the upside down "horseshoe"-shaped selection. Install the red probe from the multimeter onto terminal A, and the black probe onto terminal B of the distributor. This is called the primary winding measurement. The measurement of resistance for the primary winding should be between 0.6 and 0.8 ohms. If the resistance level on the distributor is not within these specifications, the coil should be replaced.

Install the black-and-yellow wire onto terminal A, and the white-and-blue wire onto terminal B. Install the mounting screws and tighten them snug with a Phillips screwdriver. Install the probes from the multimeter onto the distributor again. The reading for this test should be between 12,800 and 19,600 ohms. If the measurement of resistance for this test does not fall within the specifications, replace the ignition coil.

Install the distributor gasket back onto the distributor after testing is complete. Install the distributor cap and tighten the mounting screws snug with the screwdriver. Install the spark plug wires back onto the cap, matching the marked numbers on the wires with the numbers stamped into the cap.

Items you will need

  • Masking tape

  • Black marker

  • Multimeter

  • Philips screwdriver

 How to Check an Ignition Coil With a Spare Spark Plug

Select a relatively long spark plug wire to use with your tester. You want a wire long enough so you can position your tester safely away from fuel lines and fuel injector air intake to eliminate the danger of igniting any fuel or fuel vapor.

Adjust the spark gap on the spark plug that you will be using to test your ignition coil to the gap specified for the spark plugs in your engine as specified in your vehicle's service manual.

Insert one end of the spark plug wire in the tower on the ignition coil and attach the other end to the spark plug.

Wedge the spark plug tightly against a clean are of the engine block. A good ground is essential to controlling the high voltage current surge, which is what damages sensitive computers and solid state ignition components. A solid ground is also essential for the test to give you a good reading on the condition of the ignition coil. Make sure that the spark plug/tester is positioned in such a way that you have an unobstructed view of the spark plug's electrodes.

Observe the spark as a helper cranks the engine over. A solid bluish-white spark indicates a good ignition coil. If the spark appears weak, check to make sure that the wire is properly seated in the coil and firmly attached to the spark plug before you condemn the coil as being bad. Also, make sure that the spark plug is firmly grounded before you decide that the coil is bad.

Items you will need

  • Sparkplug

  • Length of sparkplug wire

  • Spark plug gapping tool

  • Vehicle service manual