Diagnostic Aids

If the vehicle is equipped with a fuel module, the module must be disconnected before performing the fuel system pressure test.
Fuel system is under pressure. To avoid fuel spillage, see FUEL SYSTEM PRESSURE RELIEF (GASOLINE) in REMOVE/INSTALL/OVERHAUL article.
On V6 or V8 engines, fuel pressure drops to almost zero psi after pump shuts "OFF".

Fig 1: Chart A-6 Schematic, Fuel System Pressure Test

Courtesy of GENERAL MOTORS CORP.

Fig 2: Flow Chart A-6, Fuel System Pressure Test

Courtesy of GENERAL MOTORS CORP.