Using a voltmeter, connect the leads to the positive
terminal of the battery and the starting motor output
With the ignition or injection system disabled,
crank the engine. Note the voltmeter reading. It should
not be over 0.5 volts. If voltage drop is greater,
something within the circuit has excessive resistance.
There may be a burned or pitted solenoid contact, loose
electrical connections, or other malfunctions. Each
component is then to be tested individually.
STARTER GROUND CIRCUIT TEST.The
starter ground circuit test checks the circuit between
the starting motor and the negative terminal of the
Using a voltmeter, connect the leads to the
negative terminal of the battery and to the end frame of
the starting motor. Crank the engine and note the
voltmeter reading. If it is higher than 0.5 volts, check
the voltage drop across the negative battery cable. The
engine may not be properly grounded. Clean, tighten,
or replace the battery cable if needed. A battery cable
problem can produce symptoms similar to a dead
battery, bad solenoid, or weak starting motor. If the
cables do NOT allow enough current to flow, the
starter will turn slowly or not at all.
REVIEW 2 QUESTIONS
What are the three types of pinion drive
mechanisms used on starting motors?
What is the only function of a starter solenoid
when it is mounted away from the starter?
What is the most likely cause of a starter making
a clicking sound?
What type of starter uses gear reduction within
the starter and gear reduction between the drive
pinion and the ring gear?
When repairing a starter, you should replace the
brushes if they are one half of their original size.
When a starter is being tested what is the
maximum amount of time the engine should be
cranked before starter damage can occur?
What test is used to check for excessive
resistance in all components between the
positive battery terminal and the starter?
components, their functions, and maintenance
The ignition circuit supplies high voltage surges
(some as high as 50,000 volts in electronic ignition
circuits) to the spark plugs in the engine cylinders.
These surges produce electric sparks across the spark
plug gaps. The heat from the spark ignites the
compressed air-fuel mixture in the combustion
chambers. When the engine is idling, the spark appears
at the spark plug gap just as the piston nears top dead
center (TDC) on the compression stroke. When the
engine is operating at higher speeds, the spark is
advanced. It is moved ahead and occurs earlier in the
compression stroke. This design gives the compressed
mixture more time to bum and deliver its energy to the
The functions of an ignition circuit are as follows:
Provide a method of turning the ignition circuit
ON and OFF.
Be capable of operating on various supply
voltages (battery or alternator voltage).
Produce a high voltage arc at the spark plug
electrodes to start combustion.
Distribute high voltage pulses to each spark plug
in the correct sequence.
Time the spark so that it occurs as the piston
nears TDC on the compression stroke.
Vary spark timing with engine speed, load, and
PRIMARY AND SECONDARY CIRCUITS
The ignition circuit is actually made of two
separate circuits which work together to cause the
electric spark at the spark plugs. These two circuits are
the PRIMARY and SECONDARY.
The primary circuit of the ignition circuit includes
all of the components and wiring operating on low
voltage (battery or alternator voltage). Wiring in the
primary circuit uses conventional wire, similar to the
wire used in other electrical circuits on the vehicle.
The secondary circuit of the ignition circuit is the
high voltage section. It consists of the wire and
components between the coil output and the spark plug
ground. Wiring in the secondary circuit must have a
thicker insulation than that of the primary circuit to
prevent leaking (arcing) of the high voltage.