GMC 1982 Light Duty Truck, Service Manual

Page: 856 / 1435

6C5-8 FUEL SYSTEM
O N -V E H IC L E S E R V IC E
F u el Line R e p a ir
R ep lacem ent
1. If replacement of a fuel feed, fuel return or emission
pipe is required use welded steel tubing meeting GM
Specification 1 24-M or its equivalent.
2. Do not use copper or aluminum tubing to replace steel
tubing. Those materials do not have satisfactory
durability to withstand normal vehicle vibrations.
3. When rubber hose is used to replace pipe, use only
reinforced fuel resistant hose which meets GM
Specification 6165-M . Hose inside diameter must
match pipe outside diameter.
4. Do not use rubber hose within 4" (100 mm) of any part
of the exhaust system or within 10" (254 mm) of the
catalytic converter.
5. In repairable areas, cut a piece of fuel hose 4" (100
mm) longer than portion of the line removed.
If more than a
6
inch (152 mm) length of pipe is
removed, use a combination of steel pipe and hose so
that hose lengths will not be more than 10 inches (254
mm).
Follow the same routing as the original pipe.
6
. Cut ends of pipe remaining on car square with a tube
cutter. Using the first step of a double flaring tool, form
a bead on the end of both pipe sections. If pipe is too
corroded to withstand bead operation without damage,
the pipe should be replaced. If a new section of pipe is
used, form a bead on both ends of it also.
7. Use screw type hose clamp. Part Number 2494772, or
equivalent. Slide clamps onto pipe and push hose 2"
(51 mm) onto each portion of fuel pipe. Tighten clamps
on each side of repair.
8
. Pipes must be properly secured to the frame to prevent
chafing.
EVAPORATIVE CONTROL SYSTEM (ECS)
G E N E R A L D E S C R IP T IO N
All light duty emissions and some heavy duty emission
vehicles are equipped with a system designed to prevent
escape of fuel vapor to the atmosphere. Vapor generated by
evaporation of fuel in the tank, previously exhausted to
atmosphere, is transferred by an emission line to the engine
compartment. During periods of operation, vapors are fed
directly to the engine for consumption. During periods of
inoperation, an activated charcoal canister located in the
emission line stores any vapor generated for consumption
during the next period of operation.
The amount of vapor drawn into the engine at any time
is too small to have any effect on fuel economy or engine
operation.
With this closed system it is extremely important that
only vapors be transferred to the engine. To avoid the
possibility of liquid fuel being drawn into the system, these
following features are included as part of the total system:
1. A fuel tank overfill protector is provided on all series to
assure adequate room for expansion of liquid fuel
volume with temperature changes.
2. A one point fuel tank venting system is provided on all
series to assure that the tank will be vented under any
conceivable vehicle attitude.
3. To protect the tank from mechanical damage in the
event of excessive internal or external pressures
resulting from the operation of this closed system, a
pressure-vacuum relief valve, located in the gas cap,
will control the tank internal pressure.
O N -V E H IC L E S E R V IC E
Maintenance requirement is that the oiled fiberglass
filter assembled in the bottom of the canister, be replaced at
intervals shown in Section 0B. Under extremely dusty
conditions, more frequent attention may be required.
Check operation of bowl vent and purge valve.
C a n is te r a n d Filter
Removal
1. Note installed position of hoses on canister.
2. Disconnect hoses from top of canister.
3. Loosen clamps and remove canister.
4. If replacing filter, pull out filter from bottom of canister
with your fingers.
Inspection
1. Check hose connection openings. Assure that they are
open.
2. Check operation of purge valve by applying vacuum to
the valve. A good valve will hold vacuum.
Installation
1. Install new filter.
2. Install canister and tighten clamp.
3. Connect hoses in same order.
C a n is te r Pu rg e V a lv e
Disassembly
1
. Disconnect lines at valve.
2. Snap off valve cap (slowly remove cap as diaphragm is
under spring tension). Remove diaphragm, spring
retainer and spring.
3. Replace parts as necessary. Check orifice openings.
Assembly
1. Install spring, spring retainer, diaphragm and cap.
2. Connect lines to valve.
Checking Purge Valve
1. Remove purge valve control vacuum line. Check for a
vacuum signal with engine operating above idle (1500
RPM). If no vacuum signal, perform EGR System
Function Check.
2. Apply an external vacuum source to the purge valve