1990 Geo Prizm Base, 4D Hatchback, AutomaticFACTORY OEM SERVICE PROCEDURE

Fuel Pressure Test

  1. Ensure battery is fully charged and ignition switch is off. Relieve fuel system pressure. See FUEL PRESSURE RELEASE. Remove banjo bolt from cold start injector fuel line.
  2. Install Fuel System "T" Fitting Adapter (J-38347) with 2 new gaskets. Install Fuel Pressure Gauge (J-34730-B). Install jumper wire between "B+" terminal and Fuel Pump (FP) terminal of diagnostic connector, located on left strut tower. Check for fuel leaks. See Fig 1 .
  3. Turn ignition switch on. Open fuel pressure gauge shut-off valve. Open gauge air-purge valve to bleed trapped air/fuel into container.
  4. With fuel pump operating and engine off, fuel pressure should be 38-44 psi (2.7-3.0 kg/cm2 ). Maximum fuel pressure (fuel line pinched) should be more than 57 psi (3.9 kg/cm2 ). With ignition and fuel pump off, fuel pressure should remain at more than 21 psi (1.5 kg/cm2 ) for at least 5 minutes. Start engine to measure fuel pressure with engine idling. Fuel pressure should be 30-33 psi (2.0-2.3 kg/cm2 ).
  5. If pressure is not within specification, check for defective fuel pump, pressure regulator or restriction in fuel system. Repair as necessary. Remove pressure gauge. Start engine and ensure no fuel leaks exist.
Fig 1: Testing Prizm Fuel System
G121591Courtesy of GENERAL MOTORS CORP.
REGULATED FUEL PRESSURE

Application (1) Pressure psi (kg/cm2 )
Prizm & Prizm GSi 30-44 (2.7-3.0)
(1) With ignition on, engine idling and fuel pressure regulator vacuum hose connected.
UNREGULATED FUEL PRESSURE

Application (1) Pressure psi (kg/cm2 )
Prizm & Prizm GSi 38-44 (2.7-3.1)
(1) Check with engine idling. Disconnect and plug fuel pressure regulator vacuum hose.
MAXIMUM FUEL PRESSURE

Application (1) Pressure psi (kg/cm2 )
Prizm & Prizm GSi More Than 57 (3.9)
(1) Fuel line pinched before inlet to TBI or fuel rail.
REST FUEL PRESSURE

Application (1) Pressure psi (kg/cm2 )
Prizm & Prizm GSi More Than 21 (1.5)
(1) Ignition switch and engine off.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.