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HOMESERVICE MANUALSPONTIAC1987FIREBIRD FORMULA, 5.0 H, AUTOMATICREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMV6/V8 PFI COMPONENT TESTCHART A7 - FUEL SYSTEM DIAGNOSIS (5.0/5.7L)CHART A7 (1 OF 2) - FUEL SYSTEM DIAGNOSIS (5.0/5.7L)
1987 Pontiac Firebird Formula, 5.0 H, Automatic

Chart A7 (1 Of 2) - Fuel System Diagnosis (5.0/5.7L)

1987 Pontiac Firebird Formula, 5.0 H, AutomaticSECTION Chart A7 (1 Of 2) - Fuel System Diagnosis (5.0/5.7L)

The ECM turns the in-tank fuel pump on for 2 seconds when the ignition is turned on. It will turn it on again during cranking and will keep it on as long as the engine is running or cranking and the ECM is receiving HEI distributor reference pulses. If there are no reference pulses, the ECM will shut the fuel pump off within 2 seconds after the key is turned on or engine is stopped. The fuel pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator, where the system pressure is controlled to 34-47 psi (2.4-3.3 kg/cm2 ) with the ignition on, engine stopped or during wide open throttle (WOT). Excess fuel is returned to the fuel tank.

NOTE: Test numbers refer to test numbers on diagnostic chart.
  1. Install Pressure Gauge (J-34730-1). Wrap a shop towel around fuel pressure tap to absorb any fuel spillage when installing gauge. With ignition on, pump pressure should be 41-47 psi (2.8-3.3 kg/cm2 ). This pressure is controlled by spring pressure within the regulator assembly.
  2. When the engine is idling, the manifold pressure is low (high vacuum). Manifold pressure is applied to the fuel regulator diaphragm. This will offset the spring and result in a lower fuel pressure. The idle pressure will vary slightly depending on barometric pressure, however, the pressure idling is less indicating pressure regulator control.
  3. Pressure that continues to fall is caused by one of the following: in-tank fuel pump check valve not holding, pump coupling hose leaking, pressure regulator valve leaking or an injector is sticking open.
  4. An injector sticking open can best be determined by checking for a fouled or fuel saturated spark plug(s). If a leaking injector can not be located by a fouled or fuel saturated spark plug the following procedure should be used: Remove plenum, cold start valve and fuel rail bolts. Reconnect cold start valve. Connect a hose to valve nozzle and insert into a gasoline container. Lift fuel rail out just enough to leave injector nozzles in the ports. Pressurize the fuel system. Lift each side of rail up and observe for injectors leaking.
  5. See TROUBLESHOOTING in the CEC TESTS W/O CODES article in this section.
CAUTION: Be sure injectors are not allowed to spray on engine and that injector retaining clips are intact.
RENDER: 1.0x

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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.