Step by step guide on how to test an automotive engine's ignition coil and trigger, this article pertains to most ignition coil systems.
Begin by watching this video and then continue down through the guide to get more tips and information.
Start with the car on level ground, in park with the emergency brake on.
Step 1 - Identify the type of ignition system to be tested, most cars, use a coil over plug (COP) type of system, there are several variations but all work on the same principal.
Step 2 - When checking for a misfire while the
engine is still running, the fuel pump must be disabled to avoid accidental ignition
discharge. Using the owners manual identify the fuse location.
Step 3 - Once the fuse is located use needle nose
pliers or a fuse removal tool to remove the fuel pump fuse from the power distribution
center (PDC.)
Step 4 - Remove the safety from the coil electrical
connector (red.) Some cars are not equipped with this feature.
Step 5 - After the safety has been removed, depress
the electrical connector tab to remove the connector from the coil assembly.
Step 6 - Once the connector has been removed, located
both terminals to be used for testing.
Step 7 - Because these terminals are small in size,
sometimes a paperclip or small wire can be inserted into the connector terminals
which makes testing easier.
Step 8 - After cutting the paperclip or wire, insert
a piece into each terminal, do not allow the wires to contact each other, this could
cause damage to the computer.
Step 9 - Once both terminals have been prepared,
use a voltmeter set to the DC voltage setting. Also install alligator clips to the
leads to ensure a good connection.
Step 10 - Next, using the voltmeter lead clips,
attach them to the paperclip wires, polarity doesn't need to be observed. (Note:
Do not allow the leads to connect during the test.)
Step 11 - After connecting the leads, turn the
ignition key to the "ON" position without cranking the engine. The voltage observed
should be 0.
Step 12 - Then, crank the engine over while observing
the meter, (engine should not start) the meter should pulsate between 0 and 12 volts.
This is confirmation that the computer coil driver is sending signal to the coil
for spark and that the ignition system is working. If no voltage is observed while
the additional coils on the system operate, check for bad wiring, or computer. If
none of the coil triggers operate suspect a crankshaft angle sensor (CKS), or computer
control relay.
Step 13 - Once this portion of the test is complete,
remove the voltmeter leads and test pins from the coil electrical connector.
Step 14 - With the electrical connector disconnected,
remove the ignition coil mounting bolt.
Step 15 - After the mounting bolt has been removed,
gently lift the coil from the plug well.
Step 16 - After gently removing the coil from the
spark plug well, insect the coil for any broken pieces or cracks in the housing
which are an indication of failure.
Step 17 - This next test will need a voltmeter
set to ohms.
Step 18 - With the coil removed, attach the voltmeter
leads to either coil terminal ( small wire connector.)
Step 19 - Once the volt meter is connected obtain
the reading provided, if this ignition coil was bad the reading would much higher.
Step 20 - After reconnecting the ignition coil
to the wiring harness, observe the electrical contact which contacts the spark plug.
Step 21 - For this portion of the test, a circuit
test light is needed which is then connected to engine ground.
Step 22 - While the grounded test light is creating
an air gap between the spark plug contact or terminal, and the tip of the test light.
Step 23 - While keeping hands clear of the test
area, have a helper crank the engine over, an electrical spark should be observed
if the coil is functioning correctly. If no spark is observed the coil has failed
and replacement is required.
Step 24 - After replacement or testing is complete,
gently reinstall the coil into the spark plug well.
Step 25 - Once the coil is in position, install
the coil mounting bolt and tighten.