Fuel Pressure

Basic diagnosis of fuel system should begin with determining fuel system pressure.

Fuel Pressure

1. Remove rear seat cushion. Disconnect fuel pump harness connector. Start engine. Let engine run until it stops. Turn ignition off. Disconnect negative battery terminal. Connect fuel pump harness connector.
   CAUTION: Use a rag to cover fuel hose connection prior to loosening bolt as there may still be residual fuel pressure in system.
2. On 1.6L engine, remove brace for access to fuel line. On all engines, disconnect fuel high pressure hose at delivery pipe. See Fig 1 . Connect hose Adapter (MD998742) and Adapter Hose (MD998709) to delivery pipe. Connect fuel hose to adapter. Connect a fuel pressure gauge to hose adapter.
3. Connect negative battery terminal. Connect battery voltage to fuel pump test terminal. Test terminal is a Black/White wire at center of firewall. Ensure no fuel leaks are present.
4. Start engine and idle. Measure fuel pressure with vacuum hose connected to fuel pressure regulator. Disconnect and plug vacuum hose from pressure regulator. Record fuel pressure readings. Refer to FUEL PRESSURE SPECIFICATIONS table.
5. Raise engine speed to 2500-3000 RPM two or three times. Ensure fuel pressure does not drop when engine returns to idle. Check for fuel pressure in fuel return hose by gently pinching hose while raising engine speed.
6. There will not be any fuel pressure in return hose if fuel volume is low. Turn engine off. If fuel pressure is lower than specification, check for a faulty fuel pressure regulator or fuel pump.
7. If fuel pressure is higher than specification, check for a faulty fuel pressure regulator or plugged fuel return line. If fuel pressure does not change when vacuum hose for regulator is connected or disconnected, check for a leaking vacuum hose.
8. Fuel pressure should not drop off. If fuel pressure drops suddenly, check for leakage in fuel pump. If fuel pressure drops slowly, check for leakage at injector. Remove fuel pressure gauge. Install a new "O" ring at end of high pressure hose.

Control Relay

This multi-purpose relay switches power to vehicle sensors and actuators including airflow sensor, crank angle sensor, idle speed control, injectors and fuel pump, (not all sensors are used on all engines). When ignition switch is turned "ON", ECU energizes coils controlling injectors, airflow sensor and idle speed control. When ignition is turned to "START" position, ECU energizes coils (through inhibitor switch on automatic transmission) to supply power to fuel pump. Relay failure will cause a no start condition. For additional testing see I - SYS/COMP TESTS article.

Fig 1: Typical Fuel Injected Engine Fuel Pressure Testing Connection

Courtesy of CHRYSLER MOTORS.