Fuel System Diagnosis

Throttle Body Pressure Test Port:

NOTE: The following test procedures assume that the ignition system is functioning, and that a good spark is evident at the plugs. If this is not the case proceed to IGNITION SYSTEMS/DIAGNOSIS AND TESTING, for testing procedures.

NO START
1. Remove the plug from the pressure test port on the throttle body.
2. Install a pressure test fitting in place of the plug, and connect a 0-207 kPa (0-30 psi) fuel pressure gauge to the test fitting.
3. Turn the ignition key ON and observe the fuel pressure gauge. The fuel pump should engage for approximately 2 seconds, and build fuel pressure to approximately 97-103 kPa (14-15 psi). If the fuel pressure reading is within this range the pump is operating correctly, and no further fuel pump testing is necessary. If the engine will not start (with good ignition spark, and adequate fuel pressure), refer to FUEL INJECTOR for additional testing.
4. If the fuel pump fails to engage, and no pump pressure is evident on the gauge, refer to FUEL PUMP RELAY, for additional testing.
5. If the fuel pump engages (listen for hum), but no pressure builds, and the engine will not start, pinch the fuel return line, and turn the ignition switch ON again. If fuel pressure builds, the regulator is defective, or out of adjustment. If no pressure builds, the pump has no output and will need to be replaced.

Fuel Pressure Regulator Adjustment:

ENGINE STARTS/POOR DRIVEABILITY
1. START the engine, and let it run at idle. With low fuel pressure, the engine may stumble and die. If the fuel pressure reading is low, turn the pressure adjusting screw inward to increase the fuel pressure to the correct range. If the fuel pressure increases to the correct range, no further testing or adjustment is required. If the fuel pressure fails to increase proceed to step 3.
2. If the fuel pressure reading is high, turn the pressure adjusting screw outward to decrease the fuel pressure to the correct range. If the fuel pressure decreases to the correct range, no further testing or adjustment is required. If the fuel pressure fails to decrease proceed to step 4.
3. If the fuel pressure remains too low after attempting to adjust the pressure, momentarily pinch the fuel return line, and check the fuel pressure reading on the gauge. If the pressure increases rapidly with the return line pinched, the fuel pressure regulator is defective, and must be replaced. If the fuel pressure fails to increase proceed to step 5.
4. If the fuel pressure remains too high after attempting adjustment, check the fuel return line, and tank fittings for obstructions. Clear any obstructions found and retest. If no obstructions are found the fuel pressure regulator is defective and must be replaced.
5. If the fuel pressure fails to increase with the fuel return line pinched off, connect an inline pressure gauge between the fuel pump and the fuel filter. If no pressure difference is noted on either pressure gauge the fuel pump is defective and must be replaced. If a 35 kPa (5 psi) or greater reading is achieved on the gauge between the pump and filter, the fuel filter is plugged and must be replaced.