FUEL PRESSURE TEST


1.Release residual pressure from the fuel pipe line to prevent fuel gush out (Refer to ).
caution Cover the hose connection with rags to prevent splash of fuel that could be caused by some residual pressure in the fuel pipe line.

2.Remove the fuel high-pressure hose at the delivery pipe.

3.Assemble the special tool called injector test set (MB992076) as shown in the figure according to the following procedure.

  1. Remove the injector installation adapter from the hose. Remove another hose together with the adapter and remove the adopter 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 (adapter hose).
  4. Install the special tool prepared in the procedure "c" to the nipple that was removed together with hose in the procedure "a".
4.Install the special tool assembled in Step 3 between the delivery pipe and fuel high-pressure hose.

<Where the fuel pressure gauge is used>
  1. Install the fuel pressure gauge on the special tool for measuring the fuel pressure via an appropriate O-ring or gasket.

<Where the fuel pressure gauge set is used>
  1. Install the special tool fuel pressure gauge set (MB991981) on the special tool for measuring the fuel pressure via an appropriate gasket.
  2. Connect the leads from the fuel pressure gauge set to the power supply (cigarette lighter socket) and special tool vehicle communication interface (V.C.I.) (MB991824).
5.
caution Connection and disconnection of M.U.T.-III should be always performed with the ignition switch turned to the LOCK (OFF) position.
Connect the M.U.T.-III to the diagnosis connector.
6.Operate the electric motor switch without depressing the brake pedal and turn ON the power supply mode of electric motor switch.
7.Select "Item No. 9" from the M.U.T.-III actuator test to drive the fuel pump. Check that there are no fuel leaks from any parts.
8.Finish the actuator test or turn off the power supply mode of the electric motor switch.
9.Set the vehicle to the continuous idling mode.
10.Measure fuel pressure.
Standard value: Approximately 324 kPa
11.Check to see that fuel pressure does not drop even after the engine has been raced several times.
12.If any of fuel pressure measured in steps 10 and 11 is out of specification, troubleshoot and repair according to the table below.
Symptom
Probable cause
Remedy

  • Fuel pressure is too low.
  • Fuel pressure drops after racing.

Clogged fuel filter
Replace the fuel filter
Fuel leaking to return side due to poor fuel regulator valve seating or settled spring.
Replace fuel pressure regulator
Low fuel pump delivery pressure
Replace fuel pump
Fuel pressure is too high.
Binding valve in fuel pressure regulator
Replace fuel pressure regulator
13.Stop the engine and check change of fuel pressure gauge reading. 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.
Symptom
Probable cause
Remedy
Fuel pressure drops gradually after engine is stopped
Leaky injector
Replace injector
Leaky fuel regulator valve seat
Replace fuel pressure regulator
Fuel pressure drops sharply immediately after engine is stopped
Check valve in fuel pump is held open
Replace fuel pump
14.Release residual pressure from the fuel pipe line (Refer to ).
caution Cover the hose connection with rags to prevent splash of fuel that could be caused by some residual pressure in the fuel pipe line.
15.Remove the fuel pressure gauge and special tool from the delivery pipe.
16.Install the fuel high-pressure hose over the delivery pipe.
17.Check for any fuel leaks by following the procedure in Step 7.
18.Disconnect the M.U.T.-III.