Hyundai Coupes/Sedans 1986-1993 Repair Guide

Electric Fuel Pump

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See Figures 1 and 2

The fuel pump's job is to draw fuel from the fuel tank, pressurize it and deliver the fuel to the fuel injectors for combustion in the cylinders. The fuel pump is located inside the fuel tank and is usually completely submerged in fuel, depending on the level of fuel in the tank. The pump is considered a wet-type pump because the inside of the pump is filled with fuel at all times. The pump and motor are cooled by the fuel passing through it. The pump is comprised of a DC motor directly coupled to an impeller type pump. The pump itself is made up of an impeller, casing and a cover with O-ring seals. Additional pump components include a relief valve and a check valve. Fuel pressurization is accomplished when the motor turns the impeller and creates a pressure differential between the bottom and the top of the impeller due to grooves in the outer circumference of the impeller. As soon as the pressure difference is created, the fuel swirling inside the pump is pressurized and flows through the motor, cooling it along the way. Fuel then flows from the motor, opens the check valve and is expelled from the discharge port.

The relief valve acts as a safety device to prevent over-pressurization of the fuel pump for any reason. In such a situation, the relief valve ball overcomes its spring pressure and lifts in response to the increase in pump pressure. The fuel is then diverted back to the suction side of the pump. The relief valve will stay open as long as the over-pressure situation exists. The check valve is a device that permits one way flow of a fluid. When the fuel pump stops, a back pressure is exerted on the check valve causing it to seal off fuel system pressure. By keeping constant pressure in the fuel system, the engine is able to be re-started more easily and vapor lock at high temperatures is prevented.



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Fig. Fig. 1: Cutaway view of the electric fuel pump



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Fig. Fig. 2: Fuel pump attaching screws

OPERATION TEST



See Figures 3 through 7

If the fuel pump does not work:

  1. Check the fuse.
  2.  



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Fig. Fig. 3: Fuel pump gasket positioning

  1. Check all wiring connections.
  2.  



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Fig. Fig. 4: Jumping the fuel pump drive terminal on Sonata



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Fig. Fig. 5: Jumping the fuel pump drive terminal-1990-93 Excel, Scoupe and Elantra

  1. Check the control relay which is located in the engine compartment, next to the ignition coil. If the engine starts when the ignition switch is turned to START , but stops when it is turned to ON , the relay is defective. Jumper terminals 1 and 2 of the test connector; the fuel pump should operate. If the pump fails to operate when the jumper is connected, the pump is probably defective.
  2.  



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Fig. Fig. 6: Checking the fuel pump pressure without a gauge



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Fig. Fig. 7: Location of the high pressure fuel connection on Sonata. This is where the fuel pressure gauge is connected

PRESSURE TESTING



See Figures 8, 9, 10 and 11



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Fig. Fig. 8: Connecting the fuel pressure gauge-Excel, Elantra and Scoupe



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Fig. Fig. 9: Connecting the fuel pressure gauge-4 cylinder engine Sonata

  1. Relieve fuel system pressure. Disconnect the battery negative cable.
  2.  
  3. Hold the upper fuel filter nut securely with a backup or spanner wrench. Cover the hoses with shop towels and remove the upper eye bolt. Discard the gaskets.
  4.  



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Fig. Fig. 10: Connecting the fuel pressure gauge-Sonata V6 engine



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Fig. Fig. 11: Disconnecting the fuel pressure regulator hose

  1. Using a fuel pressure gauge with the appropriate adapters, install the pressure gauge to the fuel filter.
  2.  
  3. Connect the negative battery terminal. Apply battery voltage to the fuel pump test connector located in the engine compartment, which will energize the fuel pump. With pressure applied, check for fuel leakage at the gauge. If no leaks are present, continue with the test procedure.
  4.  
  5. Start the engine and run at curb idle speed.
  6.  
  7. Measure the fuel pressure and compare to specifications.
  8.  
  9. Locate and disconnect the vacuum hose running to the fuel pressure regulator. Plug the end of the hose and record the fuel pressure again. The fuel pressure should have increased approximately 10 psi.
  10.  
  11. If the pressure readings were not at the desired specifications, perform the following diagnostic procedure:
    1. If fuel pressure is too low, check for a clogged fuel filter, a defective fuel pressure regulator or a defective fuel pump, any of which will require replacement.
    2.  
    3. If fuel pressure is too high, the fuel pressure regulator is defective and will have to be replaced, or the fuel return is bent or clogged. If the fuel pressure reading does not change when the vacuum hose is disconnected, the hose is clogged or the valve is stuck in the fuel pressure regulator and it will have to be replaced.
    4.  
    5. Stop the engine and check for changes in the fuel pressure gauge. It should not drop. If the gauge reading does drop, watch the rate of drop. If fuel pressure drops slowly, the likely cause is a leaking injector which will require replacement. If the fuel pressure drops immediately after the engine is stopped, the check valve in the fuel pump isn't closing and the fuel pump will have to be replaced.
    6.  

  12.  
  13. Relieve fuel system pressure.
  14.  
  15. Remove the fuel pressure gauge.
  16.  
  17. Install a new O-ring and the pressure hose to the filter. After installation, apply battery voltage to the terminal for fuel pump activation to run the fuel pump. Check for leaks.
  18.  

REMOVAL & INSTALLATION



  1. Reduce pressure in the fuel lines as follows:
    1. Turn the ignition to the OFF position.
    2.  
    3. Loosen the fuel filler cap to release fuel tank pressure.
    4.  
    5. Disconnect the fuel pump harness connector located under the rear seat cushion on Elantra or in the area of the fuel tank on the remaining models.
    6.  
    7. Start the vehicle and allow it to run until it stalls from lack of fuel. Turn the key to the OFF position.
    8.  
    9. Disconnect the negative battery cable, then reconnect the fuel pump connector.
    10.  

  2.  
  3. Raise the vehicle and support it safely.
  4.  
  5. Remove the fuel tank from the vehicle. Disconnect the hoses at the pump.
  6.  
  7. Unbolt and remove the pump from the tank.
  8.  

To install:
  1. Install the new pump with new gasket in place into the fuel tank and secure.
  2.  
  3. Install the fuel tank into the vehicle.
  4.  
  5. Connect the fuel lines and the electrical connectors to the fuel pump and sending unit.
  6.  

8.Connect the negative battery cable, pressurize the fuel system and check for leaks.

 
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