Fuel Pressure: Testing and Inspection
The content of this article and images reflects the changes identified in TSB - 10-13-008.FUEL PRESSURE TEST
Required Special Tools:
- MB991958: Scan tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991910: Main Harness A
- MB991981: Fuel Pressure Gauge Set
- MB992001: Hose Adapter
- MB992049: Quick Connector
- MB992076: Injector Test Set
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 splashing of fuel that could be caused by some residual pressure in the fuel pipe line.
2. Disconnect the fuel high-pressure hose at the fuel rail side.
3. Assemble the special tool MD998707 of special tool as shown in figure.
NOTE: The special tool MB992076 (injector test set) is compatible with the special tool MB998706 (injector test set).
In case of vehicle using (square) quick connector
W/ Square Quick Connector:
(1) Remove the injector installation adapter from the hose. Remove another hose together with the adapter and remove the adapter from the remaining hose.
(2) Install the special tool MB992049 (quick connector) and the special tool MB992001 (hose adapter) to the hose without the adapter.
(3) Remove the nipple of the bolt of the special tool MD998709 (hose adapter).
(4) Install the special tool prepared in the procedure (3) to the nipple that was removed together with hose in the procedure (1).
In case of vehicle using (round) quick connector
W/ Round Quick Connector:
(1) Remove the injector installation adapter from the hose. Remove another hose together with the adapter and remove the adapter from the remaining hose.
(2) Install the special tool MB991990 (quick connector) and the special tool MB992001 (hose adapter) to the hose without the adapter.
(3) Remove the nipple of the bolt of the special tool MD998709 (hose adapter).
(4) Install the special tool prepared in the procedure (3) to the nipple that was removed together with hose in the procedure (1).
4. Install the special tool assembled in step 3 between the fuel rail and the fuel high-pressure hose.
[When using the fuel pressure gauge]
a. Via a suitable O-ring or gasket, install the fuel pressure gauge to the special tool that has already assembled as described.
[When using the special tool MB991981 (fuel pressure gauge set)]
a. Via a gasket, install the special tool MB991981 (fuel pressure gauge set) into the special tool that has already assembled as described.
b. Connect the leads from the fuel pressure gauge set to the power supply (cigarette lighter socket) and special tool MB991824 (V.C.I).
CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
5. Connect scan tool MB991958 to the data link connector.
6. Turn the ignition switch to the ON position (But do not start the engine).
7. Use Actuator test "item number 9" to drive the fuel pump. Check that there is no fuel leaking from any section when the fuel pump is operating.
8. Finish the actuator test or turn the ignition switch to the LOCK (OFF) position.
9. Start the engine and run at idle.
10. Measure fuel pressure while the engine is running at idle.
Standard value: Approximately 260 kPa (38 psi) at curb idle
11. Remove the vacuum hose from the intake manifold and measure fuel pressure after the nipple closed with a cap.
Standard value: 310 - 345 kPa (45 - 50 psi) at curb idle
12. Check to see that fuel pressure at idle does not drop even after the engine has been revved several times.
13. Revving the engine repeatedly, hold the fuel return hose lightly with your fingers to feel that fuel pressure is present in the return hose.
NOTE: If the fuel flow rate is low, there will be no fuel pressure in the return hose.
14. If any of fuel pressure measured in Step 10 to 13 is out of specification, troubleshoot and repair according to the table below.
(Part 1):
(Part 2):
15. Stop the engine and observe fuel pressure gauge reading. It is normal if the reading does not drop within 2 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. If pressure continues to drop with fuel return line squeezed closed, injector(s) or fuel pump 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 tool from the fuel rail.
18. Fit the fuel high-pressure hose to the fuel rail.
19. Check for fuel leaks.
1. Use scan tool MB991958 to operate the fuel pump.
2. Check the fuel line for leaks and repair as needed.
20. Disconnect scan tool MB991958.