Fuel Pressure Test

Required Special Tools:
MB991502: Scan Tool
MD998709: Adaptor Hose
MD998742: Hose Adaptor




1. Release residual pressure from the fuel line to prevent fuel spray.

WARNING: To prevent a fire, cover the hose connection with shop towels to prevent splash of fuel that could be caused by some residual pressure in the fuel pipe line.

2. Disconnect the high-pressure fuel hose at the fuel rail side.




3. Assemble special tool, MD998709 and special tool MD998742.
4. Place a suitable O-ring or gasket on the assembled special tools MD998709 and MD998742 and install the fuel pressure gauge.




5. Install special tools MD998742 and MD998709 between the fuel rail and the high-pressure fuel hose.




6. Connect scan tool MB991502 to the data link connector.
7. Use actuator test 25 to drive the fuel pump. Check that there is no fuel leaking from any section when the fuel pump is operating.
8. Stop the fuel pump.
9. Start the engine and run at idle.
10. Measure fuel pressure while the engine is running at idle.

Standard value;
Approximately 270 kPa (38 psi) at curb idle




11. Disconnect the vacuum hose from the fuel pressure regulator and measure fuel pressure with the hose end closed by a finger.

Standard value: 330 - 350 kPa (47-50 psi) at curb idle

12. Check to see that fuel pressure at idle does not drop even after the engine has been raced several times.

NOTE: If the fuel flow rate is low, there will be no fuel pressure the return hose.

13. Racing the engine repeatedly, hold the fuel return hose lightly with fingers to feel that fuel pressure is present in the return hose.




14. If any of fuel pressure measured in steps 10 to 13 is out of specification, troubleshoot and repair according to the table.
15. Stop the engine and observe fuel pressure gauge reading. Normal if the reading does not drop within two minutes. If it does, observe the rate of drop and troubleshoot and repair according to the table below. Start, then stop the engine.
(1) Squeeze the fuel return line closed to confirm leak-down occurs from defective fuel pressure regulator.
(2) Squeeze the fuel supply line closed to confirm leak-down occurs from defective fuel pump check valve.




(3) If pressure continues to drop with both fuel lines squeezed closed, injector(s) are leaking.
16. Release residual pressure from the fuel pipe line.

WARNING: Cover the hose connection with shop towels to prevent splash of fuel that could be caused by some residual pressure in the fuel pipe line.




17. Remove the fuel pressure gauge and special tools MD998709 and MD998742 from the fuel rail.
18. Replace the O-ring at the end of the high-pressure fuel hose with a new one.
19. Fit the high-pressure fuel hose into the fuel rail and tighten the bolts to specified torque.

Tightening torque: 5 N-m (3.6 lb-ft)

20. Check for fuel leaks.
(1) Use scan tool MB991502 to operate the fuel pump.
(2) Check the fuel line for leaks, repair as needed.
21. Disconnect scan tool MB991502.