Pontiac FIREBIRD 1972 Service Manual page 661

ENGINE FUEL 6B-7
/
4 BBL. CARB. ENGINE
2 BBL. CARB. ENGINE
TO ENGINE
Fig. 6B-9 Accelerator Controls
-
F Series
to expel the fuel through the outlet valve to the carburetor
bowl.
Because the diaphragm is moved downward only by the
diaphragm spring, the pump delivers fuel to the carbu-
retor only when the pressure in the outlet line is less than
the pressure maintained by the diaphragm spring. Fuel is
delivered to the carburetor only when the needle valve is
open. When the needle valve is closed by pressure of fuel
on the float, the pump builds up pressure in the space
below the diaphragm and in the outlet tube until the dia-
phragm spring is compressed. The diaphragm then re-
mains stationary until more fuel is required.
There are no repairs possible to the fuel pump and when
a malfunction is detected, it will be necessary to replace
the pump assembly.
TROUBLE DIAGNOSIS AND TESTING
There are three tests that can be performed to evaluate the
fuel pump without removing the pump from the engine.
It is important that the pump performs properly using all
three tests:
1. Be sure there is gasoline in the tank.
2. Check for loose line connections. A leak at the pres-
sure side of the system (line from pump to carbu-
retor) will be indicated by dripping fuel. A leak in the
suction side of the system (line from gas tank to
pump) will not be apparent except in its effect of
reducing v o l ~ m e of fuel on the pressure side of the
system.
3. Look for bends or kinks in lines or hoses which will
reduce flow. Check the fuel pump inlet hose routing
.
to be sure it is not bent or kinked.
I. FUEL FLOW TEST
1. Ground primary terminal of distributor with jumper
lead so that engine can be cranked without firing.