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FUEL SYSTEM
6C-67
The Key Buzzer is fed by the ORANGE wire from the
CLOCK LIGHTER COURTESY fuse at the fuse panel. It
buzzes when the PINK BLK STR wire is grounded through
the Key switch in the steering column (key in ignition) and
driver's door jamb switch (door open).
The instrument panel gage unit gets feed through the
PINK wire from the GAUGES fuse. The TAN wire connects
the gage to a variable resistance ground through the sending
unit in the fuel tank.
Fuel Pump
-
Mechanical
The fuel pump is a diaphragm type pump and is actuated
by the rocker arm through a link and a pull rod (see Fig.
6C- 1).
Many cars have a special fuel pump which has a
metering outlet for a vapor return system. Any vapor which
forms is returned to the fuel tank along with hot fuel through
a separate line. This greatly reduces any possibility of vapor
lock by keeping cool fuel from the tank constantly circulating
through the fuel pump.
Fuel Tank and Lines
All series have a fuel tank mounted in the rear of the
vehicle. All fuel tanks have an emission pipe going to the
charcoal canister for venting purposes and a fuel feed pipe
for delivery of fuel to the engine. Some vehicles have a third
pipe, called vapor return pipe, which returns fuel and vapors
from the fuel pump to the fuel tank. The vapor return pipe
permits continuous circulation of fuel through the fuel feed
pipe and reduces the possibility of vapor lock. The fuel feed
pipe is 3/8" diameter. The emission pipe is 5/16" diameter.
The vapor return pipe is 1/4" diameter.
Evaporative Emission Control System (EEC)
All Pontiacs 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 charcoail 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 car attitude. This is accomplished by using a
dome type fuel tank on Sedans and Coupes.
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.
ON-CAR SERVICE
Fuel Filter
The carburetor inlet fuel filter should be replaced every
15,000 miles or 12 months.
After assembling any filter element in the carburetor,
always start the engine and check for leaks in the fuel line
and fittings before installing the air cleaner.
Other Filters or Strainers
A woven plastic filter is located on the lower end of the
fuel pickup pipe in the gas tank. This filter prevents dirt from
entering the fuel line and also stops water unless the filter
becomes completely submerged in water. This filter is self
cleaning and normally requires no maintenance. Fuel
stoppage at this point indicates that the gas tank contains an
abnormal amount of sediment or water; the tank should
therefore be removed and thoroughly cleaned.
Fuel Pump Inspection and Test
If the fuel system is suspected of delivering an improper
amount of fuel to the carburetor, it should be inspected and
tested in the car, as follows:
Inspection of Fuel System
1. Make certain that there is gasoline in the tank.
2. With the engine running, inspect for leaks at all
gasoline feed hose connections from fuel tank to carburetor.
Tighten any loose connections. Inspect all hoses for flattening
or kinks which would restrict the flow of fuel. Air leaks or
restrictions on suction side of mechanical fuel pump will
seriously affect pump output.
3. Inspect for leaks at fuel pump diaphragm flange.
4. Disconnect feed pipe near carburetor. Disconnect
distributor feed wire so that engine can be cranked without
firing. Place suitable container at end of pipe and crank
engine a few revolutions. If no gasoline, or only a little flows
from the pipe, the feed line is clogged or fuel pump is
inoperative. Before suspecting the fuel pump, disconnect feed
line at both ends and blow through it with air hose to make
certain the fuel pipe is clear. Re-check fuel pump capacity.
Fuel Pump Pressure Test
1.Disconnect gasoline line near carburetor and connect
a suitable pressure gage (such as Pressure-Leakdown Tester
J-22109).
2. Start engine and check pressure with engine running
at slow idle speed. Fuel pump pressure should be as specified
at the end of this section. On cars equipped with a vapor
return system, squeeze off the return hose so that an accurate
reading can be obtained.
3. If fuel pump pressure is below minimum, pump must
be replaced.
Fuel Pump Flow Test
1. Disconnect fuel line from carburetor. Run fuel line
into a suitable measuring container.
2. While observing the sweep second hand of a clock or
watch, run the engine at idle until there is one pint of fuel
in the container. One pint should be pumped in 30 seconds
or less.
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