Fuel Pressure
WARNING:
Before disconnecting high pressure fuel hose at fuel delivery pipe, cover fuel hose connection with a rag. Some residual fuel pressure may still be in system.
- Relieve fuel pressure. See RELIEVING FUEL PRESSURE . Disconnect high pressure fuel inlet line at fuel rail. Connect fuel pressure gauge with Adapters (MD998709 and MD998742) between fuel rail and high pressure fuel inlet line. See Fig 1. Use scan tool to operate fuel pump. Ensure no fuel leaks are present.
- Start engine and allow it to idle. Measure fuel pressure with vacuum hose connected to fuel pressure regulator. Record fuel pressure reading. See FUEL PUMP PERFORMANCE . Disconnect vacuum hose from fuel pressure regulator and plug vacuum hose end. Record fuel pressure reading.FUEL PUMP PERFORMANCE
Application At Idle W/Vacuum - psi (kPa) At Idle W/O Vacuum - psi (kPa) All Models 38 (270) 47-50 (330-350) - Race engine several times. Fuel pressure should not drop. Check that fuel pressure is present in fuel return hose by gently squeezing hose while racing engine. If fuel volume is low, fuel pressure in return hose will not be felt.
- If fuel pressure is lower than specification, fuel pressure drops when racing engine, or no fuel pressure in fuel return hose can be felt, check for clogged fuel filter, faulty fuel pressure regulator or fuel pump delivery pressure.
- If fuel pressure is greater than specification, check for a faulty fuel pressure regulator or plugged fuel return line. If fuel pressure does not change when vacuum hose to regulator is connected or disconnected, check for a leaking or clogged vacuum hose to fuel pressure regulator, or faulty fuel pressure regulator.
- Stop engine. Observe fuel pressure reading for 2 minutes. Pressure should hold steady. If pressure drops sharply immediately after engine is stopped, the check valve in fuel pump is stuck open. If fuel pressure gradually drops after engine is stopped, restart engine and bring fuel pressure back up.
- Stop engine. While observing fuel pressure, squeeze fuel return line closed to check for fuel regulator as source of leak down. Squeeze high pressure fuel inlet line closed to check for fuel pump check valve as source of leak down. Squeeze both lines closed to check for injectors as source of leak down.
- When fuel pressure test is complete, repeat fuel pressure release procedure before disconnecting fuel pressure gauge. Install NEW "O" ring at end of high pressure fuel inlet line. Connect high pressure fuel inlet line to fuel rail. Tighten bolts to 44 INCH lbs. (5 N.m). Use scan tool to operate fuel pump and check for fuel leaks.