TESTING

Fuel Pump Operation Check

1. Set the ignition switch to the OFF position.
2. Check that when battery voltage is directly applied to the fuel pump check terminal located in the engine compartment, the operating sound of the fuel pump can be heard.

   NOTE: Since the fuel pump is located in the fuel tank, its operating sound cannot be readily heard. Remove the fuel tank cap and listen to the operating sound through the filler port.

   Fig. 1: Checking fuel pump operation with battery voltage applied to the fuel pump check terminal — 1990–94 2.0L engine shown

   Fig. 2: Location of the fuel pump drive connector — 1995–98 2.0L turbo and 2.4L engines shown

3. Hold the high pressure fuel hose between your fingers and check that the fuel pressure in the lines can be felt.

Pressure Testing

EXCEPT 1995–98 2.0L NON-TURBO ENGINES

1. Relieve the fuel system pressure as outlined earlier.

   CAUTION
   Cover the hose connection with a shop towel to prevent the splash of fuel that can be caused by residual pressure in the fuel pipe line.

2. Disconnect the high pressure fuel line from the fuel rail.

   Fig. 3: Location of the high pressure fuel hose and fuel rail — 1990–94 vehicles

   Fig. 4: High pressure fuel hose location — 1995–98 2.0L turbo and 2.4L engine

3. On 1990–94 2.0L engine, remove the throttle body stay.

   Fig. 5: If necessary, remove the throttle body stay

4. Connect a fuel pressure gauge to tools MD998709 and MD998742 or exact equivalent, with appropriate adapters, seals and/or gaskets to prevent leaks during the test. Install the gauge and adapter between the delivery pipe and high pressure hose.

   Fig. 6: Exploded view of the fuel pressure gauge and adapter set

   Fig. 7: Install of the fuel pressure gauge on the fuel rail — 2.0L engine shown, others similar

5. Connect the negative battery cable.
6. For 1990–94 vehicles, apply battery voltage to the terminal for fuel pump check terminal located in the engine compartment. Run the fuel pump and check for leaks at the pressure gauge connection.
7. For 1995–98 vehicles, connect the fuel pump drive terminal to the positive battery terminal using a jumper wire to drive the fuel pump. Check the fuel pressure gauge and tool connections for leaks. Disconnect the jumper wire from the fuel pump drive terminal to stop the fuel pump.
8. Start the engine and run at curb idle speed.
9. For 1995–98 vehicles, measure the fuel pressure. For 2.0L turbo engines, the pressure should be 33 psi (230 kPa). For 2.4L engines, the fuel pressure should be 38 psi (270 kPa).
10. Locate and disconnect the vacuum hose from the fuel pressure regulator. Plug the end of the hose. Measure the fuel pressure and compare with the following specifications:

    Fig. 8: Disconnect and plug the regulator vacuum hose, then measure the fuel pressure

    1. 1990–94 non turbo engines:47–50 psi (330–350 kPa).
    2. 1990–94 turbo engines with manual transaxle:36–38 psi (250–270 kPa).
    3. 1990–94 turbo engines with automatic transaxle: 41–46 psi (290–320 kPa).
    4. 1995–98 2.0L turbo engines: 42–45 psi (289–309 kPa).
    5. 2.4L engines: 47–50 psi (330–350 kPa).
11. For 1990–94 vehicles, reconnect the pressure regulator vacuum hose, then measure the fuel pressure (engine idling) and compare with the following specifications:
    1. 1990–94 non turbo engines:38 psi (270 kPa).
    2. 1990–94 turbo engines with manual transaxle:27 psi (190 kPa).
    3. 1990–94 turbo engines with automatic transaxle: 33 psi (230 kPa).
12. After the fuel pressure stabilizes, race the engine 2–3 times and check that the fuel pressure does not fall when the engine is running at idle.
13. Check to be sure there is fuel pressure in the return hose by gently pressing the fuel return hose with fingers while racing the engine.

    NOTE: There will be no fuel pressure in the return hose when the volume of fuel flow is low.

14. If the results fall outside of specification, refer to the following:
    • 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.
    • 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.
15. 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.
16. Relieve fuel system pressure.
17. Disconnect the high pressure hose and remove the fuel pressure gauge from the delivery pipe.
18. Install a new O-ring in the groove of the high pressure hose. Connect the hose to the delivery pipe and tighten the screws. After installation, apply battery voltage to the terminal for fuel pump activation to run the fuel pump. Check for leaks.
19. Reinstall the throttle body stay, if removed.

1995–98 2.0L NON-TURBO ENGINES

NOTE: Testing the fuel pressure on these vehicles requires the use of a scan tool.

1. Properly relieve the fuel system pressure.
2. Remove the protective cover from the service valve on the fuel rail.
3. Connect Fuel Pressure Gauge MB995051 to the service valve.

   Fig. 9: Attach the fuel gauge to the service valve on the fuel rail

   NOTE: When using the scan tool fuel system test, the fuel pump relay stays energized for 7 minutes, until the test is stopped or until the ignition switch is turned of the

   OFF position.

4. Turn the ignition key to the ON position. Use a suitable scan tool to access the "Fuel System Test". This test will activate the fuel pump and pressurize the system. The fuel pressure should be around 47–50 psi (330–350 kPa).
5. Use the scan tool to pressurize the fuel system, then make sure there is no fuel leakage from the service valve.
6. If the results fall outside of specification, refer to the following:
   • 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.
   • 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.
7. Using the scan tool, with the ignition key ON, repeat the fuel system test.
8. Turn the ignition switch OFF, then check the gauge reading. It's normal if the reading does not drop in about 2 minutes. If it does, check the rate of the drop and compare with the following:
   • If the fuel pressure drops gradually, you have either a leaky injector or fuel regulator valve seat and the defective component should be replaced.
   1. If the fuel pressure drops sharply, check that the valve in the fuel pump is held open. If not, replace the fuel pump.
9. After testing has been completed, remove the fuel pressure gauge and install the protective cover onto the fuel rail service valve.