GM Storm/Spectrum 1985-1993 Repair Guide

Mechanical Fuel Pump

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REMOVAL & INSTALLATION



See Figures 1 and 2

The mechanical fuel pump for Carbureted Spectrum vehicles is located on the engine at the side of the cylinder head intake manifold. It is driven by a camshaft lobe which contacts and pumps the fuel pump rocker arm/lever.

  1. Tag and disconnect the fuel hoses from the pump assembly.
  2.  
  3. Remove the retaining bolts from the fuel pump and heat insulator assembly.
  4.  
  5. Remove the fuel pump from the engine.
  6.  
  7. Cover the fuel pump mounting face on the cylinder head to prevent the discharge of oil and to prevent the entry of dirt or contaminants.
  8.  

To install:
  1. Clean the cylinder head and fuel pump mating surfaces.
  2.  
  3. Attach the fuel pump, along with the new heat insulator assembly, to the cylinder head. Depending on camshaft position, it may be difficult to install the pump. Make sure the pump rocker arm is properly in contact with the camshaft or camshaft driver.
  4.  
  5. Hold the pump in position, then install and tighten the retaining bolts.
  6.  
  7. Connect the fuel hoses to the pump assembly.
  8.  
  9. Start the engine and carefully check for leakage or proper operation.
  10.  



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Fig. Fig. 1: Mechanical fuel pump location



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Fig. Fig. 2: Cut-away view of the mechanical fuel pump assembly

TESTING



See Figures 3, 4, 5 and 6

If a fuel pump problem is suspected, the fuel pump must be removed from the engine for testing.

  1. Make a visual inspection of the pump casing for cracks and other damage. If cracks or other visible damage are present, the pump assembly must be replaced.
  2.  
  3. Check for excessive wear between the rocker arm and the camshaft contact faces. The pump must be replaced, if excessive wear is found.
  4.  
  5. Before proceeding with pump testing, the pump valve seals must be moistened by pouring a small amount of fuel into the pump.
  6.  
  7. Remove the rocker arm spring, then measure the force and play of the rocker arm by moving the arm.
  8.  
  9. Check the inlet valve:
    1. Move the rocker arm to the pump side and hold it in this position.
    2.  
    3. Shut both the return and outlet pipes.
    4.  
    5. Allow the rocker arm to return to it's original position.
    6.  
    7. When the rocker arm is returned, there should be a noticeable increase in the amount of play.
    8.  
    9. If play doe not increase, replace the pump.
    10.  

  10.  
  11. Check the outlet valve:
    1. Cover the inlet pipe and attempt to move the rocker arm.
    2.  
    3. The rocker arm must not move when the inlet pipe is closed, but DO NOT apply excessive force to the rocker arm.
    4.  
    5. The fuel pump must be replaced, if there is excessive play.
    6.  

  12.  
  13. Check the diaphragm:
    1. Cover the inlet, outlet and return pipes, then attempt to move the rocker arm.
    2.  
    3. The rocker arm must not move when the pipes are closed, but DO NOT apply excessive force to the rocker arm.
    4.  
    5. The fuel pump must be replaced, if the rocker arm moves.
    6.  

  14.  
  15. Check the oil seal:
    1. Cover the air pipe, then attempt to move the rocker arm.
    2.  
    3. The rocker arm must not move when the air pipe is closed, but DO NOT apply excessive force to the rocker arm.
    4.  
    5. The fuel pump must be replaced, if the rocker arm moves.
    6.  

  16.  



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Fig. Fig. 3: Checking the fuel pump inlet valve



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Fig. Fig. 4: Checking the fuel pump outlet valve



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Fig. Fig. 5: Checking the fuel pump diaphragm



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Fig. Fig. 6: Checking the oil seal

 
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