1. Verify the Problem:
* Confirm No Fuel: Is the engine definitely not getting fuel *from the injectors*? Don't just assume—you need to confirm this. You can:
* Listen Carefully: With the ignition on, you might hear a faint clicking sound from the injectors. This is normal operation. If you hear absolutely nothing, it's a strong indicator of a problem.
* Check for Fuel Pressure: Measure the fuel pressure at the TBI fuel rail. Your 1990 Impala should have a fuel pressure specification (check your owner's manual or a repair manual). Low or no pressure eliminates the injectors as the primary suspect.
* Inspect Injectors Directly (Advanced): If you're comfortable working with fuel systems (and have the proper safety precautions in place), you can momentarily disconnect the fuel rail and crank the engine. Observe if fuel is spraying from the injectors. *Use extreme caution when handling fuel systems.*
2. Check the Obvious:
* Fuel Pump: If fuel pressure is low or nonexistent, the fuel pump is the most likely culprit. Listen for the fuel pump to activate when the ignition is switched on (you should hear a brief hum).
* Fuel Filter: A clogged fuel filter will restrict fuel flow, leading to low pressure.
* Fuses and Relays: Check the fuses and relays associated with the fuel pump and the TBI system. Your owner's manual or a repair manual will show their locations.
* Ignition System: A faulty ignition system (e.g., distributor, ignition module, crankshaft position sensor) can prevent the injectors from receiving the signal to fire, even if the fuel system is fine.
3. Diagnose TBI System Specifics:
* Throttle Position Sensor (TPS): A faulty TPS can prevent the engine control module (ECM) from sending the signal to open the injectors. This sensor monitors throttle position and adjusts fuel delivery accordingly. A multimeter can test its voltage output.
* Injector Wiring and Connectors: Inspect the wiring and connectors leading to the injectors for any damage, corrosion, or loose connections. A broken wire or corroded connector will prevent the electrical signal from reaching the injectors.
* Engine Control Module (ECM): The ECM controls the fuel injectors. A faulty ECM is less common but possible. Testing an ECM usually requires specialized equipment.
* Injector Driver Circuit (within ECM): The ECM contains a circuit that drives the injectors. A malfunction in this circuit would require a thorough electrical diagnosis.
4. Seeking Professional Help:
If you're not comfortable working with fuel systems or automotive electrical systems, take your Impala to a qualified mechanic. Troubleshooting TBI systems can be complex, and improperly working with fuel systems can be dangerous.
Important Safety Note: Fuel is highly flammable. Always work in a well-ventilated area, away from open flames or sparks. Disconnect the battery negative terminal before working on any electrical components. If you're unsure about any step, consult a repair manual or a professional mechanic.
