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Computer Basics
This section explains the engine
computer control system, the types of
sensors and how the computer controls
fuel delivery, idle speed, spark timing
and emission devices.
The following is a general introduction to
computer controlled engine systems.
Additional information may be found in
books dealing with this subject available
at your local library or auto parts store.
The more you know about the computer
system, the better and faster you can
troubleshoot and fix problems.
Why Computers?
Computer controls were installed in
vehicles to meet Federal Government
regulations for lower emissions and
better fuel economy. This all began in the
early 1980’s when purely mechanical
control systems just were not good
enough anymore. A computer could be
programmed to precisely control the
engine under various operating
conditions and eliminate some mechani-
cal parts making the engine more
reliable.
What the computer controls
The main control areas of the computer
are:
• Fuel delivery
• Idle speed
• Spark advance timing
• Emission devices (EGR valve, carbon
cannister,etc.)
Some early systems only controlled fuel
delivery. The other functions were added
soon after.
The changes made to the basic engine
to allow a computer to control these
tasks are the only differences between
an older engine and a computerized one.
A little later we will discuss just how the
computer handles these tasks.
What has NOT changed?
A computer controlled engine is basically
the same as earlier types. It is still an
internal combustion engine with pistons,
spark plugs, valves and cams. The
ignition, charging, starting, and exhaust
systems are almost the same, as well.
You test and repair these systems the
same way as before, using familiar tools.
The instruction manuals for these tools
show you how to perform the tests. Your
compression gauge, vacuum pump,
dwell-tach meter, engine analyzer, timing
light, etc., are still valuable!
The Engine Computer Control
System
The computer module is the “heart” of
the system. It is sealed in a metal box
and linked to the rest of the system by a
wiring harness. The computer module is
located in the passenger compartment,
usually under the seat, behind the
dashboard or front kick panels. This
protects the electronics from moisture,
extreme temperatures and excess
vibration, which are common in the
engine compartment.
Summary of Contents for Code Scanner CP9025
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