Chevrolet Full Size Cars 1979-1989

Electric Fuel Pump

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TESTING





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Fig. Fig. 1 Fuel pump control schematic 1986 vehicles (1985 similar)



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Fig. Fig. 2 Fuel pump control schematic 1987-89 vehicles

  1. Properly relieve the fuel system pressure.
  2.  
  3. Raise and support the vehicle safely using jackstands.
  4.  
  5. Disconnect the fuel supply line between the fuel filter (usually located along the frame rails near the tank) and the throttle body.
  6.  
  7. Install a fuel pressure gauge, such as J-29658 or equivalent, inline between the fuel filter and throttle body unit. If necessary use an adapter or Tee fitting in order to connect the gauge and complete the fuel circuit.
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A Tee fitting may be fabricated for this purpose. Depending on the fuel gauge, short lengths of steel tubing, appropriately sized flare nuts and a flare nut adapter may be used.

  1. Turn the ignition ON , but do not start the engine. Within 2 seconds of turning the ignition ON pressure should be 9-13 psi (62-90 kPa). If necessary, cycle the ignition OFF , then ON again, in order to build up system pressure.
  2.  
  3. If the fuel pump did not run or system pressure did not reach specification, locate the fuel pump test connector. The test connector is usually found on the passenger side of the engine compartment, with a single red wire leading from the relay to the connector. Using a jumper wire, apply battery voltage to the test connector in order to energize and run the fuel pump. The pump should run and produce fuel pressure of 9-13 psi (62-90 kPa). If the pump does not run, check the relay and fuel pump wiring.
  4.  
  5. If the pump pressure was lower than specification, first check for a restricted fuel line or filter and replace, as necessary. If no restrictions can be found, restrict the fuel supply line between the pressure gauge and the TBI unit (a flexible hose may be temporarily clamped to produce the restriction), disengage the injector connector, then apply voltage to the test connector again. If pressure is now above 13 psi (90 kPa), replace the faulty pressure regulator. If pressure remains below 9 psi (62 kPa), then the problem is in located in the fuel tank (the fuel pump, coupling hose or inlet filter).
  6.  
  7. If during Step 7, the pressure was higher than specification, disengage the injector connector, then disconnect the fuel return line flexible hose which connects the line from the throttle body to the tank line. Attach a 5 / 16 ID flex hose to the fuel line from the throttle body and place the other end into an approved gasolin