FUEL PRESSURE TEST

Required Special Tools: • MB991958: Scan Tool (MUT-III Sub Assembly) MB991824: V.C.I MB991827: USB Cable MB991911: Main Harness B • MB991637: Fuel Pressure Gauge Set • MD998709: Adaptor Hose • MD998742: Hose Adaptor 1.Release residual pressure from the fuel line to prevent fuel spray. (Refer to .) 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 fuel pressure measurement tools as follows. <When using the fuel pressure gauge>

1.Remove the union joint and bolt from special tool MD998709 (adapter hose) and instead attach special tool MD998742 (hose adapter) to the adapter hose. 2.Place a suitable O-ring or gasket on the assembled special tools MD998709 and MD998742 and install the fuel pressure gauge. 3.Install the assembled fuel pressure measurement tools between the fuel rail and fuel high-pressure hose. <When using special tool MB991637 (fuel pressure gauge set)>

1.Remove the union joint and bolt from special tool MD998709 (adapter hose) and instead attach special tool MD998742 (hose adapter) to the adapter hose. 2.Install special tool MB991637 (fuel pressure gauge set) into assembled special tools MD998709 and MD998742 via a gasket. 3.Install the assembled fuel pressure measurement tools between the fuel rail and fuel high-pressure hose.

To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958. 4.Connect scan tool MB991958 to the data link connector. 5.Use Actuator test 07 to drive the fuel pump. Check that there is no fuel leaking from any section when the fuel pump is operating. 6.Stop the fuel pump. 7.Start the engine and run at idle. 8.Measure fuel pressure while the engine is running at idle. Standard value: Approximately 270 kPa (79.7 in.Hg) at curb idle

9.Disconnect the vacuum hose (blue stripe) from the fuel pressure regulator and measure the fuel pressure with the hose end closed with your finger. Standard value: 330 - 350 kPa (97 - 103 in.Hg) at curb idle 10.Check to see that fuel pressure at idle does not drop even after the engine has been revved several times. 11.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. 12.If any of fuel pressure measured in steps 8 to 11 is out of specification, troubleshoot and repair according to the table below. SYMPTOM PROBABLE CAUSE REMEDY Fuel pressure too low Fuel pressure drops after racing No fuel pressure in fuel return hose Clogged fuel filter Replace 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 too high Binding valve in fuel pressure regulator Replace fuel pressure regulator Clogged fuel return hose or pipe Clean or replace hose or pipe Same fuel pressure when vacuum hose is connected and when disconnected Damaged vacuum hose or clogged nipple Replace vacuum hose or clean nipple Defective fuel pressure regulator Replace fuel pressure regulator 13.Stop the engine and observe fuel pressure gauge reading. It is 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. 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 .) 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. 15.Remove the fuel pressure gauge, and special tools MD998709, MD998742 and MB991637 from the fuel rail. 16.Replace the O-ring at the end of the fuel high-pressure hose with a new one. 17.Fit the fuel high-pressure hose into the fuel rail and tighten the bolts to specified torque. Tightening torque: 4.9 N·m (43 in-lb) 18.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. 19.Turn the ignition switch to the "LOCK" (OFF) position. 20.Disconnect scan tool MB991958.