Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSPONTIAC1990FIREBIRD TRANS AM, 5.0 F, STANDARDREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROLS - BASIC TESTINGBASIC FUEL SYSTEM CHECKSFUEL SYSTEM PRESSURE TEST (EFI)FUEL PRESSURE CHECK (THROTTLE BODY INJECTION)
1990 Pontiac Firebird Trans Am, 5.0 F, Standard
Fuel Pressure Check (Throttle Body Injection)
1990 Pontiac Firebird Trans Am, 5.0 F, StandardSECTION Fuel Pressure Check (Throttle Body Injection)
- Relieve fuel pressure (if necessary). Remove air cleaner and plug thermal vacuum port on throttle body. When removing fuel line, always use 2 wrenches. Install Fuel Pressure Gauge (J-29658B or BT-8205) and Adapter (J-29658-85) in fuel line between steel line and flexible hose.NOTE: DO NOT pinch off fuel return line completely. DO NOT exceed pressure build-up of more than 32 psi (2.0 kg/cm2 ) on 2.5L "W" Body or 13 psi (.9 kg/cm2 ) on all other models as regulator may be damaged.
- Turn ignition on and observe fuel pressure reading. Fuel pressure should read 26-32 psi (1.8-2.2 kg/cm2 ) on 2.5L "W" Body (VIN R) or 9-13 psi (.6-.9 kg/cm2 ) on all other models . If no fuel pressure is indicated, go to step 5). If fuel pressure is okay but engine will not start, proceed to NO START DIAGNOSIS. If fuel pressure is present but is too high, go to step 4). If fuel pressure is present but is too low, gradually pinch off fuel return line to fuel tank.
- If fuel pressure remains low, check for plugged fuel filter or restriction in fuel delivery line. If filter is okay and no restrictions are present, replace fuel pump. If fuel pressure increases when return line is pinched, replace fuel pressure regulator.
- If fuel pressure is present but is higher than specification, check for restriction in fuel return line. If return line is not restricted, replace fuel pressure regulator.
- If no fuel pressure is observed, turn ignition off. Apply battery voltage to fuel pump test connector using a 10-amp fused jumper wire. For location of fuel pump test connector, refer to COMPONENT LOCATIONS in appropriate SYSTEM/COMPONENT TESTS article. Observe fuel pressure reading. If fuel pressure is still not evident, check wiring between test connector and fuel pump. If wiring is okay, replace fuel pump.
- If fuel pressure is present with voltage applied to test connector, test fuel pump relay and voltage supply to relay. Refer to the appropriate SYSTEM/COMPONENT TESTS article.
- After all repairs, allow fuel pressure to dissipate. Remove fuel pressure gauge and reconnect fuel line. Start engine and watch for fuel system leaks. For further details on fuel pressure testing, proceed to the appropriate SYSTEM/COMPONENT TESTS article.
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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.