Chart A-7B, Fuel System Diagnosis - Pressure Check

NOTE: Test numbers refer to test numbers on diagnostic chart.

1. This check is found in BASIC TESTING under FUEL PRESSURE TESTING.
2. Restricted flow causing pressure drop. Normally a vehicle with a fuel pressure of less than 32 psi at idle will not be driveable. However, if the pressure drop occurs only while driving, the engine will normally surge then stop as presssure begins to drop rapidly to zero.
3. Restricting the fuel return line allows the fuel pump to develop its maximum pressure (dead head pressure). When ignition in ON the pump should be able to develop pressure greater than 56.9 psi.
4. This test determines if the high fuel pressure is due to restricted fuel return line, or a throttle body pressure regulator problem.

Fig 1: Fuel Line Schematic

Courtesy of GENERAL MOTORS CORP.

Fig 2: Chart A-7B Diagnostic Flow Chart

Courtesy of GENERAL MOTORS CORP.