Instead of trying to "adjust" the EFI, you need to diagnose *why* it's running lean. Here are the potential causes and how to address them:
* Mass Airflow Sensor (MAF) Issues: A faulty MAF sensor provides inaccurate air readings to the computer, leading to a lean condition. This is a very common cause. The solution is to replace the MAF sensor. Don't clean it; usually, cleaning doesn't reliably restore its accuracy.
* Oxygen Sensor (O2 Sensor) Problems: A bad O2 sensor provides incorrect feedback to the computer about the air/fuel mixture, potentially leading to a lean condition. Replacing a faulty O2 sensor is the solution.
* Fuel Pressure Issues: Low fuel pressure prevents the injectors from delivering enough fuel. Check the fuel pressure using a fuel pressure gauge. Low pressure could indicate a faulty fuel pump, clogged fuel filter, or other fuel system problems.
* Vacuum Leaks: Vacuum leaks introduce unmetered air into the engine, making the computer think less fuel is needed. Inspect all vacuum lines for cracks or disconnections. Pay close attention to the intake manifold and PCV system.
* Injector Problems: Clogged or faulty fuel injectors can also lead to a lean condition. This is less common but possible. Testing injectors requires specialized equipment.
* Throttle Position Sensor (TPS) Issues: A faulty TPS provides incorrect throttle position information, which can affect the fuel delivery.
* Computer (ECM) Problems: In rare cases, a failing Engine Control Module (ECM) can cause fueling problems. This is usually the last thing to suspect and requires more advanced diagnostic tools.
How to Proceed:
1. Get a scan tool: A scan tool that reads OBD1 codes (your 1993 Chevy uses OBD1) is essential. These codes provide clues about what might be wrong. Auto parts stores often have loaner tools.
2. Check for OBD1 codes: Follow the instructions for your specific scan tool to retrieve any diagnostic trouble codes (DTCs).
3. Address the codes: Based on the codes, you can narrow down the potential problems. For example, a code related to the MAF sensor strongly suggests replacing that sensor.
4. Check fuel pressure: Measure fuel pressure using a gauge. This helps eliminate fuel delivery issues.
5. Inspect vacuum lines: Visually inspect all vacuum lines for cracks, leaks, or loose connections.
6. Professional Help: If you're uncomfortable with automotive diagnostics and repairs, take your vehicle to a qualified mechanic specializing in older vehicles. Improperly addressing a lean condition can cause significant engine damage.
Trying to adjust fuel delivery directly without understanding the underlying cause is highly discouraged. It's crucial to diagnose the problem properly before attempting any repairs. Remember, a lean condition is harmful to your engine.
