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.
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  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.
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  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.
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  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).
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  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 gasoline container. Cycle the ignition in order to energize the fuel pump and watch system pressure. If pressure is still higher, check for restrictions in the throttle body return line. Repair or replace the line if restrictions are found or replace the faulty pressure regulator if no other causes of high pressure are identified. If fuel pressure is normal only with the flexible hose-to-fuel tank line out of the circuit, check that line for restrictions and repair or replace, as necessary.
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  9. Once the test is completed, depressurize the fuel system and remove the gauge.
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  11. Secure the fuel lines and check for leaks.
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  13. Remove the jackstands and carefully lower the rear of the vehicle.
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REMOVAL & INSTALLATION





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Fig. Fig. 3 Fuel supply schematic Throttle Body Injection (TBI) system



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Fig. Fig. 4 Example of a common intank fuel pump assembly

  1. Properly relieve the fuel system pressure.
  2.  
  3. Disconnect the negative battery cable.
  4.  
  5. Raise the rear of the vehicle and support safely using jackstands.
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  7. Drain the fuel tank, then remove it from the vehicle.
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  9. Using a hammer and a drift punch, carefully drive the lockring (located on top of the fuel tank) for the fuel level sending unit/pump assembly counterclockwise. Lift the assembly from the tank.
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  11. Remove the pump from the sending unit assembly. Pull the pump up into the attaching hose while pulling it outward away from the bottom support. Be careful not to damage the rubber insulator and strainer during removal. After the pump assembly is clear of the bottom support, pull it out of the rubber connector.
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To install:

  1. Inspect the fuel pump attaching hose for any signs of deterioration and replace, as necessary. Also, check the rubber sound insulator at bottom of pump.
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  3. Push the fuel pump assembly into the attaching hose.
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  5. Install the fuel level sending unit/pump assembly into the tank using a new O-ring.
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Special care should be taken when installing the pump assembly to the tank not to fold or twist the fuel strainer or flow will be restricted.

  1. Install the lockring and secure the sending unit/pump assembly by turning the lockring clockwise.
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  3. Install the fuel tank to the vehicle.
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  5. Remove the jackstands and carefully lower the vehicle.
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  7. Connect the negative battery cable, then start the engine and check for leaks.
  8.  

 
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