Natural Gas Engines

WARNING: Fuel system remains under high pressure even when engine is not running. To avoid injury, release fuel pressure before disconnecting any fuel system hose or component. See appropriate FUEL SYSTEM PRESSURE RELEASE procedure under FUEL SYSTEM VENTING in appropriate REMOVAL & INSTALLATION article.

NOTE: Not all natural gas vehicles are equipped with Fuel Rail Pressure (FRP) sensor. On vehicles without FRP sensor, use values supplied by fuel rail pressure gauge.

1) Check Fuel Pressure
Turn ignition switch to OFF position. Connect scan tool to Data Link Connector (DLC). Install Natural Gas Fuel Rail Pressure Gauge Tool Kit (134-00114) to fuel rail Schrader valve. Using scan tool, access FRP PID (if available) from PID/DATA MONITOR & RECORD menu. With ignition switch turned to ON position, record FRP sensor PID or fuel pressure gauge reading. Start engine and allow to idle. Again record FRP sensor PID or fuel pressure gauge reading. Increase engine speed to 2500 RPM and maintain for one minute. Record FRP sensor PID or fuel pressure gauge reading. Compare measured fuel pressure to fuel pressure specification. See FUEL PRESSURE SPECIFICATIONS . If fuel pressure readings are within specification, turn ignition switch to OFF position and go to next step. If fuel pressure readings are not within specification, turn ignition switch to OFF position and go to TEST HB, step 1) under SYSTEM TESTS in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article for fuel delivery system diagnosis.

2) Check Fuel System For Pressure Stability

With fuel pressure gauge installed, cycle ignition switch from OFF to ON position 2 times to pressurize fuel system (DO NOT start engine). Verify no external leaks are present. If fuel pressure does not remain within 10 psi (69 kPa) of highest fuel pressure reading after 2 minutes, go to TEST HB, step 1) under SYSTEM TESTS in SELF-DIAGNOSTICS - EEC-V - CNG, FLEX-FUEL & GASOLINE article for fuel delivery system diagnosis. If fuel pressure remains within 10 psi (69 kPa) of highest fuel pressure reading after 2 minutes, go to next step.

3) Check Fuel System For Pressure Stability With Ignition Switch Turned To ON Position

Using scan tool, access FRP PID (if available) from PID/DATA MONITOR & RECORD menu. If FRP PID is not available, ensure natural gas fuel rail pressure gauge tool kit is installed onto fuel rail Schrader valve. Cycle ignition switch from OFF to ON (DO NOT start engine). Monitor fuel pressure reading. If fuel pressure does not remain within 10 psi (69 kPa) of highest fuel pressure reading after 10 seconds, check for leaking fuel injectors or fuel pressure regulator. If fuel pressure remains within 10 psi (69 kPa) of highest fuel pressure reading after 10 seconds, fuel system is mechanically okay.