Fuel Pump Test
- Begin basic diagnosis of fuel system by determining fuel system pressure. On 2.5L, 3.0L and 5.9L engines, release fuel pressure. See FUEL PRESSURE RELEASE. Disconnect fuel supply hose. Connect fuel system pressure Gauge (C-4799-B) between fuel supply hose and engine fuel line.
NOTE:
On 3.3L, 3.9L and 5.2L, vacuum supply line at fuel pressure regulator must be disconnected to obtain accurate pressure readings.
- On 3.3L, 3.9L and 5.2L, disconnect vacuum supply line from fuel pressure regulator. Release fuel pressure. See FUEL PRESSURE RELEASE. Connect fuel pressure gauge at fuel rail test port.
- On all models, turn ignition switch to ON position. Using Diagnostic Readout Box (DRB-II), activate fuel pump. If fuel pump pressure is at specification, fuel system is functioning properly. See FUEL PUMP PRESSURE SPECIFICATIONS table.
- If fuel pressure is less than specification, record pressure. Repeat FUEL PRESSURE RELEASE procedure. Install fuel pressure gauge in fuel supply line at rear of vehicle between fuel tank and fuel filter.
- Using DRB-II, activate fuel pump. Record pressure reading. If fuel pressure is 5 psi (.35 kg/cm2
) more than first pressure reading, replace fuel filter.
- If no change in pressure reading is observed, gently squeeze fuel return hose. If fuel pressure increases, replace fuel pressure regulator. If no change in fuel pressure is observed, problem is plugged fuel pump filter sock or defective fuel pump.
- If fuel pressure is more than specification, repeat fuel pressure release procedure. See FUEL PRESSURE RELEASE. Ensure fuel tank is at least half full. Remove fuel return hose at chassis line at fuel tank. Connect an extension hose to return hose. Place hose in an approved container with at least a 2 gallon capacity.
- Using DRB-II, activate fuel pump. If fuel pressure is now within specification, check in-tank return fuel hose for kinking. Replace fuel pump assembly if in-tank reservoir check valve or aspirator jet is plugged.
- On 2.5L and 5.9L, remove fuel return hose from throttle body if fuel pressure is still more than specification. Connect a substitute hose to throttle body return nipple. Place other end of hose in an approved container. On 3.0L and 3.3L, remove fuel return hose from fuel tubes at engine. Connect Fuel Test Connect Adapter (6541) to fuel return hose, and place other end in an approved container.
- Using DRB-II, activate fuel pump. If fuel pressure is at specification, check for a restricted fuel return line between throttle body, or fuel tubes at engine, and fuel tank. If no change is observed, replace fuel pressure regulator.
FUEL PUMP PRESSURE SPECIFICATIONS
| Application |
psi (kg/cm2
) |
| 2.5L |
39 (2.7) |
| 3.0L & 3.3L |
48 (3.4) |
| 3.9L & 5.2L |
39 (2.7) |
| 5.9L |
14.5 (1.0) |