fundamentally working-delivering
voltage to the spark plugs. A
hard-starting or poor-running engine,
however, may indicate a problem with
how well the spark is delivered. Faulty
or worn ignition components, such as
old spark plugs, or an individual coil
problem may be the cause.
WARNING!
Inefficient combustion (rich air/fuel
mixture) can cause elevated
hydrocarbon exhaust emissions and
catalytic converter damage. For this
reason, if a severe misfire is
detected, the fuel injector will be
turned off to the specific cylinder
and the MIL illuminated.
One way to diagnose a faulty coil on a
car that is running is to use an
oscilloscope to analyze spark quality.
The illustrations show normal scope
trace of spark at idle.
Table b
lists common ignition coil
voltage faults and related causes.
Note:
Note the length of sparking period and
the up-down voltage attenuations. A
short sparking period and/or an
irregular/low voltage attenuation usually
indicates a faulty coil.
A normal oscilloscope pattern for a six
cylinder engine.
1 -
Start of ignition voltage peak
2 -
Level of ignition voltage
3 -
Level of combustion voltage
4 -
Period of combustion
5 -
Combustion curve characteristics
6 -
Start of decay process
Ignition System
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