Maintenance Schedule - GMC G Service Manual

6E1-2 CARBURETOR EMISSIONS
SUBJECT
Evaporative Emission Control System (EECS).................................................................................................... 6E1-18
Description...........................................................................................................................................................6E1-18
Diagnosis of EECS.............................................................................................................................................. 6E1-20
On-Vehicle Service — EECS.............................................................................................................................. 6E1-20
Air Injection Reaction (AIR) System......................................................................................................................6E1-21
Description...........................................................................................................................................................6E1-21
Diagnosis of AIR.................................................................................................................................................. 6E1-23
On-Vehicle Service — AIR.................................................................................................................................. 6E1-26
Exhaust Gas Recirculation (EGR) System...........................................................................................................6E1-34
Description........................................................................................................................................................... 6E1-34
Diagnosis of EGR................................................................................................................................................ 6E1-34
On-Vehicle Service — EGR................................................................................................................................ 6E1-35
Early Fuel Evaporation System (EFE)...................................................................................................................6E1-37
Description........................................................................................................................................................... 6E1-37
Diagnosis of EFE................................................................................................................................................. 6E1-38
On-Vehicle Service — EFE................................................................................................................................. 6E1-40
Positive Crankcase Ventilation (PCV)...................................................................................................................6E1-43
Description........................................................................................................................................................... 6E1-43
Diagnosis of PCV................................................................................................................................................ 6E1-43
On-Vehicle Service — PCV................................................................................................................................ 6E1-44
Thermostatic Air Cleaner (THERMAC)..................................................................................................................6E1-44
Description........................................................................................................................................................... 6E1-44
Diagnosis of THERMAC...................................................................................................................................... 6E1-45
On-Vehicle Service — THERMAC.......................................................................................................................6E1-46
Throttle Return Control (TRC) System..................................................................................................................6E1-47
Description........................................................................................................................................................... 6E1-47
Diagnosis of TRC................................................................................................................................................ 6E1-48
On-Vehicle Service — TRC................................................................................................................................ 6E1-49
DRIVEABILITY
The driveability diagnosis procedures apply to various
systems in current GM vehicles. The procedures assume
that the vehicle worked right at one time and the problem is
due to time, wear, dirt or other causes. Start with the intro­
duction that follows. This will describe a systematic diag­
nostic procedure.
Any system disconnected during diagnosis should be
reconnected. This includes wires, hoses, linkage, etc.
When removing air cleaner, plug hose fittings that could
cause an air leak.
EMISSIONS
The exhaust emission control systems used on General
Motors engines perform a specific function to lower exhaust
emissions while maintaining good fuel economy and
driveability.

MAINTENANCE SCHEDULE

Refer to the Maintenance Schedule in MAINTENANCE
AND LUBRICATION (SEC. OB) for the maintenance ser­
vice that should be performed to retain emission control
performance.
CONTENTS (CONT.)
GENERAL INFORMATION
VEHICLE EMISSION CONTROL
INFORMATION LABEL
The Vehicle Emission Control Information label (Fig. 1)
contains important emissions specifications and setting
procedures. In the upper left corner is exhaust emission
information which identifies the year, the manufacturing
division of the engine, the displacement in liters of the
engine, the class of vehicle and type of fuel metering. Also,
there is an illustrated emission component and vacuum
hose schematic. This label is located in the engine com­
partment of every General Motors Corporation vehicle. If
the label has been removed, it can be ordered from service
parts.
VISUAL/PHYSICAL UNDER-HOOD
INSPECTION
One of the most important checks that must be done as
part of any diagnostic procedure is a careful visual/physical
under-hood inspection. This can often lead to fixing a prob­
lem without further steps. Inspect all vacuum hoses for cor­
rect routing, pinches, cuts, or disconnects. Be sure to
inspect hoses that are difficult to see beneath the air
cleaner, compressor, generator, etc. Inspect all the wires in
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