* Fuel Pump itself: Even though you replaced the relay, the pump itself could be failing. It might be weak and not delivering enough pressure, or it might be intermittently failing. You could try measuring fuel pressure at the fuel rail (requires a fuel pressure gauge) to see if the pump is delivering sufficient pressure. Low pressure is a strong indicator of a failing pump.
* Clogged Fuel Line: A clog somewhere in the fuel line, between the tank and the engine, could be restricting fuel flow. This is less likely if the fuel filter is new and clean, but it's still possible, especially if there's debris in the tank.
* Fuel Pressure Regulator: This regulator controls fuel pressure in the system. A faulty regulator could be leaking fuel or not maintaining the correct pressure. Again, a fuel pressure gauge is needed to diagnose this.
* Ignition System Issues (beyond distributor wires): While you've replaced the distributor cap and rotor (assuming that's what you mean by "distributor wires"), there could still be issues with the ignition coil, ignition module (often called the "ignition control module" or ICM), or even a faulty crankshaft position sensor (CKP sensor). These components are crucial for spark, and problems with them can mimic fuel delivery issues.
* Fuel Tank: It's less common, but a problem within the fuel tank itself (e.g., debris, a collapsed fuel pickup tube) could prevent fuel from being drawn properly.
Next Steps:
1. Fuel Pressure Test: This is the most important next step. Rent or borrow a fuel pressure gauge and test the pressure at the fuel rail. Your car's repair manual will specify the correct pressure. Low or fluctuating pressure points directly to a fuel delivery problem.
2. Visual Inspection of Fuel Lines: Carefully inspect the fuel lines for any kinks, cracks, or damage.
3. Check for Spark: Using a spark tester or even just a screwdriver with an insulated handle, check for spark at the spark plugs. If there's no spark, the problem lies in the ignition system.
4. Consider Professional Help: If you're not comfortable performing these checks or doing further troubleshooting, it's best to take your car to a qualified mechanic. They have the tools and expertise to diagnose the problem more efficiently.
Remember safety first! Work with the engine off and disconnect the battery negative terminal before working on any fuel system components. Gasoline is flammable and dangerous.
