Here's a general overview, but do not rely on this as a complete guide. Significant variations exist depending on the exact engine and equipment in your car.
Fuel Filter Replacement (Generally Easier):
1. Safety First: Disconnect the negative battery terminal. This prevents accidental sparks near fuel lines.
2. Locate the Filter: The fuel filter location varies by model year and engine. Your repair manual will pinpoint its exact location. It's often near the fuel tank or along the fuel line.
3. Prepare: You'll need new fuel filter (ensure correct part number for your model), wrenches (likely various sizes), rags, and a container to catch spilled fuel (fuel is flammable!).
4. Release Pressure: Some systems require releasing fuel pressure before disconnecting lines. Your repair manual will detail this process – it might involve using a pressure release valve or repeatedly turning the ignition key.
5. Disconnect Lines: Carefully loosen and disconnect the fuel lines connected to the filter. Have rags ready to absorb any spilled fuel. It's a good idea to mark which line goes where to avoid mistakes during reassembly.
6. Remove the Filter: Carefully remove the filter using the appropriate wrenches.
7. Install New Filter: Install the new filter, ensuring it's oriented correctly (often there's an arrow indicating flow direction).
8. Reconnect Lines: Reconnect the fuel lines, tightening them securely but not over-tightening.
9. Reconnect Battery: Reconnect the negative battery terminal.
10. Check for Leaks: Start the engine and check for fuel leaks around the filter and connections.
Fuel Pump Replacement (Significantly More Difficult):
Replacing the fuel pump is considerably more challenging and often requires dropping the fuel tank. This is not a job for beginners.
1. Safety First: Disconnect the negative battery terminal. Depressurize the fuel system as described above.
2. Access the Fuel Tank: This usually involves lowering the fuel tank, which is a significant undertaking. This requires disconnecting fuel lines, electrical connections, and possibly support straps. Your repair manual will guide you through this process. Often you need to drain the fuel tank first (take proper safety precautions when handling fuel).
3. Remove the Pump: Once the tank is lowered, you can access the fuel pump. This often involves removing a retaining ring or other fastening mechanism.
4. Install the New Pump: Install the new fuel pump, ensuring all seals and gaskets are properly seated.
5. Reassemble: Reinstall the fuel tank, reconnect fuel lines, electrical connections, and any other components you disconnected.
6. Reconnect Battery: Reconnect the negative battery terminal.
7. Check for Leaks & Operation: Start the engine and check for fuel leaks and proper operation of the fuel system.
Again, I strongly advise against attempting either repair without a detailed repair manual specific to your 1987 300GL. Incorrect procedures can lead to serious injury or damage to your vehicle. If you are not comfortable with these repairs, it's best to have a qualified mechanic perform them.
