Checking Fuel Pressure (Vehicles With Fuel Rail Test Port)

Relieve fuel pressure. On vehicles with vacuum assisted fuel pressure regulators, disconnect vacuum hose from fuel pressure regulator before checking fuel pressure. Remove fuel rail test port protective cap. Connect Fuel Pressure Gauge (C-4799) to fuel rail test port.
CAUTION: DO NOT activate fuel pump for long periods, or engine may hydrostatically (liquid) lock.
Turn ignition switch to ON position. Using Diagnostic Readout Box (DRB), select ASD FUEL SYSTEM TEST mode. In this mode, DRB energizes Auto Shutdown (ASD) relay, causing fuel pump to activate and pressurize fuel system.
Note fuel pressure, and record reading. Deactivate fuel pump. Relieve fuel pressure. Remove fuel pressure gauge. Reactivate fuel pump. Ensure fuel does not leak from fuel rail test port. Deactivate fuel pump. Install fuel rail test port protective cap.
If fuel pressure is within specification, fuel system is functioning properly and further testing is not required. See FUEL SYSTEM PRESSURE SPECIFICATIONS table. If fuel pressure is greater than specification, go to step 7). If fuel pressure is less than specification, install Fuel Pressure Gauge (C-4799) and appropriate fuel pressure test adapter in fuel supply line between fuel tank and fuel filter.
Using DRB, repeat ASD FUEL SYSTEM TEST. If fuel pressure is at least 5 psi greater than fuel pressure recorded in step 3), replace fuel filter. If no change in fuel pressure is observed, gently squeeze fuel return hose.
If fuel pressure increases while squeezing fuel return hose, replace fuel pressure regulator. If fuel pressure does not change while squeezing fuel return hose, check for plugged fuel inlet strainer or defective fuel pump. Repair as necessary.
Remove fuel return hose from fuel pump at fuel tank. Connect fuel pressure test adapter to return hose. Place other end of adapter into an approved gasoline container (minimum 2 gallon size).
Turn ignition switch to ON position. Repeat ASD FUEL SYSTEM TEST. If fuel pressure is now correct, replace fuel pump assembly. See FUEL SYSTEM PRESSURE SPECIFICATIONS table. If pressure is still greater than specification, deactivate fuel pump. Remove fuel pressure test adapter, and connect fuel pump return hose.
Disconnect fuel return hose from chassis fuel lines at engine. Connect fuel pressure test connector adapter to fuel return hose. Place other end of hose in approved gasoline container. Repeat ASD FUEL SYSTEM TEST.
If fuel pressure is now correct, check for restricted fuel return line. If no change is observed, replace fuel pressure regulator.

FUEL SYSTEM PRESSURE SPECIFICATIONS

Application	psi (kg/cm² )
3.3L	55 (3.9)

WARNING: Perform fuel pump test with fuel tank at least half full. Before disconnecting fuel lines or fuel system components, relieve fuel pressure. See appropriate RELIEVING FUEL PRESSURE procedure.