Repair Pontiac Mid-size 1974-1983 Repair Guide

Mechanical Fuel Pump

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Fuel pumps used on all engines are of the single-action mechanical type. The fuel pump rocker arm is held in constant engagement with the eccentric on the camshaft by the rocker arm spring. As the end of the rocker arm which is in contact with the eccentric moves upward, the fuel link pulls the fuel diaphragm downward. The action of the diaphragm enlarges the fuel chamber, drawing fuel from the tank. Fuel flows to the carburetor only when the pressure in the outlet line is less than the pressure maintained by the diaphragm spring.

The fuel pumps on all engines are not serviceable and must be replaced if defective.

REMOVAL & INSTALLATION





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Fig. Fig. 1 Fuel pump mounting-inline 6-cylinder engine shown



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Fig. Fig. 2 The fuel pump is easily accessible from under the vehicle



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Fig. Fig. 3 To remove the fuel pump, detach the rubber fuel inlet hose from the pump



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Fig. Fig. 4 When disconnecting the pump outlet fitting, ALWAYS use a back-up wrench (see arrow)



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Fig. Fig. 5 After disconnecting the outlet line, unfasten the retaining bolts, then remove the fuel pump

  1. Locate the fuel pump on the side of the cylinder block and disconnect the fuel lines.
  2.  
  3. Remove the two pump mounting bolts.
  4.  

On 305 and 350 Chevrolet-built engines: if the pushrod is to be removed, take out the two adaptor bolts and lockwashers and remove the adaptor and gasket. For installation use heavy grease to hold the pushrod in place. Coat the pipe plug threads or adaptor gasket with sealer if pushrod was removed.

  1. Remove the pump and the gasket.
  2.  
  3. Use a new gasket when installing the pump.
  4.  
  5. Install the fuel lines, start the engine and check for leaks.
  6.  

TESTING



The fuel line from the tank to the pump is the suction side of the system and the line from the pump to the carburetor is the pressure side of the system. A leak on the pressure side, therefore, would be made apparent by dripping fuel, but a leak on the suction side would not be apparent except for the reduction of the volume of fuel on the pressure side.

  1. Tighten any loose line connections and look for bends or kinks.
  2.  
  3. Disconnect the fuel pipe at the carburetor. Disconnect the distributor-to-coil primary wire so that the engine can be cranked without firing. Place a container at the end of the pipe and crank the engine a few revolutions. If little or no gasoline flows from the open end of the pipe, the fuel pipe is clogged or the pump is defective.
  4.  
  5. If fuel flows from the pump in good volume from the pipe at the carburetor, check fuel pressure to be certain that the pump is operating within specified limits as follows:
  6.  
    1. Attach a fuel pump pressure test gauge to the disconnected end of the pipe;
    2.  
    3. Run the engine at approximately 450 to 1,000 rpm on the gasoline still remaining in the carburetor bowl. Note the reading on the pressure gauge.
    4.  
    5. If the pump is operating properly the pressure will be within the specifications listed in the "Tune-Up Specifications" chart found in . The pressure will remain constant between speeds of 450 to 1,000 rpm. If the pressure is too low or too high at different speeds, the pump should be replaced.
    6.  


There are no adjustments that can be made on these fuel pumps.

 
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