A mechanical pump is used on all carbureted engines, except the 8-460 (7.5L) engine. The mechanical fuel pump is camshaft eccentric-actuated and located on the left side of the engine.
Incorrect fuel pump pressure and low volume (flow rate) are the two most likely fuel pump troubles that will affect engine performance. Low pressure will cause a lean mixture and fuel starvation at high speeds and excessive pressure will cause high fuel consumption and carburetor flooding.
To determine that the fuel pump is in satisfactory operating condition, tests for both fuel pump pressure and volume should be performed.
The tests are performed with the fuel pump installed on the engine, and with the engine at normal operating temperature and at idle speed.
Before the tests, make sure that the replaceable fuel filter has been changed at the proper distance (miles/kilometers) interval. If in doubt, install a new filter.Pressure Test
- Remove the air cleaner assembly. Disconnect the fuel inlet line of the fuel filter at the carburetor. Use care to prevent fire, due to fuel spillage. Place an absorbent cloth under the connection before removing the line to catch any fuel that might flow out of the line.
- Connect a pressure gauge, a restrictor and a flexible hose between the fuel filter and the carburetor.
- Position the flexible hose and the restrictor so that the fuel can be discharged into a suitable, graduated container.
- Before taking a pressure reading, operate the engine at the specified idle rpm and vent the system into the container by opening the hose restrictor momentarily.
- Close the hose restrictor, allow the pressure to stabilize and note the reading. The pressure should be 5 psi. (34.5 kPa).
If the pump pressure is not within 4-6 psi (27.5-41 kPa)and the fuel lines and filter are in satisfactory condition, the pump is defective and should be replaced.
If the pump pressure is within the proper range, perform the test for fuel volume.Volume Test
- Operate the engine at the specified idle rpm.
- Open the hose restrictor and catch the fuel in the container while observing the time it takes to pump 1 pint (0.47 l). On engines through 1973, it should take 30 seconds to pump 1 pint (0.47 l) of fuel. On 1974 and later engines, 1 pint (0.47 l) should be pumped in 20 seconds. If the pump does not operate to specifications, check for proper fuel tank venting or a restriction in the fuel line leading from the fuel tank to the carburetor before replacing the fuel pump.
REMOVAL & INSTALLATION
- Disconnect the fuel inlet and outlet lines at the fuel pump. Discard the fuel inlet retaining clamp.
- Remove the pump retaining bolts then remove the pump assembly and gasket from the engine. Discard the gasket.
- If a new pump is to be installed, remove the fuel line connector fitting from the old pump and install it in the new pump.
- Remove all gasket material from the mounting pad and pump flange. Apply oil resistant sealer to both sides of a new gasket.
- Position the new gasket on the pump flange and hold the pump in position against the mounting pad. make sure that the rocker arm is riding on the camshaft eccentric.
- Press the pump tight against the pad, install the retaining bolts and alternately torque them to 12-15 ft. lbs. (16-20 Nm) on all 6-cylinder engines; 20-24 ft. lbs. (27-33 Nm) on the 8-302 (5.0L); 14-20 ft. lbs. (19-27 Nm) on the 8-351 (5.8L); 19-27 ft. lbs. (26-37 Nm) on the 8-400 (6.6L) and 8-460 (7.5L). Connect the fuel lines. Use new clamp on the fuel lines.
- Operate the engine and check for leaks.