GM Full Size Vans 1967-1986 Repair Guide

Mechanical Fuel Pump

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The fuel pump is a single action AC diaphragm type. All fuel pumps used on inline and V8 engines in vans are diaphragm type and because of design are serviced by replacement only. No adjustments or repairs are possible.

The pump is operated by an eccentric on the camshaft. On six cylinder engines, the eccentric acts directly on the pump rocker arm. On V8 engines, a pushrod between the camshaft eccentric and the fuel pump operates the pump rocker arm.

TESTING



Fuel pumps should always be tested on the vehicle. The larger line between the pump and tank is the suction side of the system and the smaller line, between the pump and carburetor, is the pressure side. A leak in the pressure side would be apparent because of dripping fuel. A leak in the suction side is usually only apparent because of a reduced volume of fuel delivered to the pressure side.

  1. Tighten any loose line connections and look for any kinks or restrictions.
  2.  
  3. Disconnect the fuel line at the carburetor. Disconnect the distributor-to-coil primary wire. Place a container at the end of the fuel line and crank the engine a few revolutions. If little or no gasoline flows from the line, either the fuel pump is inoperative or the line is plugged. Disconnect the line at the pump and the tank; blow through the line with compressed air and try again. Reconnect the line. If the problem is traced to the tank, the tank and gauge unit must be removed to check the condition of the inlet filter screen. See Body & Trim for tank removal.
  4.  
  5. If fuel flows in good volume, check the fuel pump pressure to be sure.
  6.  
  7. Attach a pressure gauge to the pressure side of the fuel line.
  8.  
  9. Run the engine and note the reading on the gauge. Stop the engine and compare the reading with the specifications listed in the Tune-Up Specifications chart. If the pump is operating properly, the pressure will be as specified and will be constant at idle speed. If pressure varies or is too high or low, the pump should be replaced.
  10.  
  11. Remove the pressure gauge.
  12.  

REMOVAL & INSTALLATION



See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: Common mechanical fuel pump used on GM full-size vans


CAUTION
Never smoke when working around gasoline! Avoid all sources of sparks or ignition. Gasoline vapors are EXTREMELY volatile!

When you connect the fuel pump outlet fitting, always use 2 wrenches to avoid damaging the pump.

  1. Disconnect the fuel intake and outlet lines at the pump and plug the pump intake line.
  2.  
  3. On V6 and V8 engines, you can remove the upper bolt from the right front engine mounting boss (on the front of the block) and insert a long bolt to hold the fuel pump pushrod.
  4.  
  5. Remove the two pump mounting bolts and lockwashers; remove the pump and its gasket.
  6.  
  7. If the rocker arm pushrod is to be removed from the V6s and V8s, remove the two adapter bolts and lockwashers and remove the adapter and its gasket.
  8.  
  9. Install the fuel pump with a new gasket reversing the removal procedure. Heavy grease can be used to hold the fuel pump pushrod up when installing the pump, if you didn't install the long bolt in Step 2. Coat the mating surfaces with sealer.
  10.  
  11. Connect the fuel lines an check for leaks.
  12.  

 
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