bearings, camshaft bearings, and valve train components.
These are high-friction points in the engine and need oil
for protection.
Ignition System
An ignition system is needed on a gasoline engine to
ignite and burn the air-fuel mixture. It must increase
battery voltage enough to produce a high-voltage electric
arc, or “spark,” at the tip of each spark plug in the combus-
tion chamber. Refer to Figure 1-23.
A fundamental ignition system consists of a spark
plug, plug wire, ignition coil, switching device, and power
source. On many late-model vehicles, the ignition coil is
mounted directly on top of the spark plug eliminating the
need for a spark plug wire.
The switching device in the ignition system is an elec-
tronic control unit that makes and breaks electrical current
flow to the ignition coil(s). Ignition coil operation is timed
with crankshaft rotation so that the spark occurs in the
combustion chamber at the end of the compression stroke.
The ignition coil is used to step up battery voltage to
over 60,000 volts. This is enough voltage to make the elec-
tricity jump the spark plug gap. The ignition coil fires every
time the switching device stops current flow from the
battery, Figure 1-23. This causes the magnetic field in the
coil to collapse and induce a higher voltage in the coil’s
output wire.
The spark plug is the “match” that starts the air-fuel
mixture burning in the combustion chamber. When
ignition coil fires and sends current through the spark plug
wire, an electric arc (spark) forms at the tip of the spark
plug. This makes the fuel and air start to burn, producing
the power stroke.
Note: Older ignition systems used a
mechanical switching device called
points. Ignition systems with points have
not been used on production vehicles since the
mid 1970s. If you encounter this type of ignition
system, refer to the appropriate service manual for
service procedures.
Starting System
The starting system turns the engine crankshaft until
the engine can begin running on its own power. It uses a
battery, ignition switch, high-current relay, and electric
motor to rotate the crankshaft, Figure 1-24.
Chapter 1 Review of Engine Operation 19
Throttle body
Intake port
Valve
cover
Exhaust
port
Exhaust
manifold
Intake
runners
Intake manifold
Fuel injector Air
Figure 1-20. This is a cutaway of an engine. Note the intake and exhaust manifolds. Ports in the intake manifold connect to the intake
ports in the cylinder head. The exhaust manifold is bolted over the exhaust ports in the cylinder head. (General Motors)