Here's a breakdown of likely culprits and troubleshooting steps:
* Fuel Pump: The most probable cause. Even if you checked the *filter*, the pump itself might be weak, failing, or simply not getting enough power. A weak pump struggles to deliver sufficient fuel at lower throttle positions, but might manage a burst of pressure when the pedal is floored.
* Fuel Pressure Regulator: This component regulates fuel pressure within the system. A faulty regulator might allow fuel to leak back into the tank, reducing pressure and making starting difficult.
* Clogged Fuel Injectors: While less likely to cause this *exact* symptom, partially clogged injectors could restrict fuel flow enough to prevent starting, especially at lower throttle positions. Flooring the pedal might briefly overcome this restriction in some cases.
* Crankshaft Position Sensor (CKP) or Cam Position Sensor (CMP): These sensors are crucial for ignition timing. A malfunctioning sensor could cause erratic starting or no start at all, but it's less likely to be connected to the behavior you're describing. However, it shouldn't be entirely ruled out.
Troubleshooting Steps:
1. Check Fuel Pressure: This is the most crucial step. You need a fuel pressure gauge to measure the fuel pressure at the fuel rail. Compare your reading to the factory specifications for your vehicle. Low pressure strongly suggests a fuel pump or regulator problem.
2. Inspect the Fuel Filter (Again): Even if you checked it, make absolutely sure there is no blockage or restriction. Sometimes, a seemingly clean filter can still have a partial blockage.
3. Check for Fuel Leaks: Visually inspect the fuel lines, connections, and the fuel pressure regulator for any leaks. A leak will reduce system pressure.
4. Test the Fuel Pump Relay: A faulty relay can prevent the pump from receiving power.
5. Consider a Professional Diagnosis: If you're uncomfortable working with fuel systems (which are potentially dangerous), it's best to take your vehicle to a qualified mechanic. They have the tools and expertise to properly diagnose the problem.
Important Safety Note: Gasoline is highly flammable. Take necessary precautions when working with fuel systems. Disconnect the battery's negative terminal before starting any work. Work in a well-ventilated area and avoid sparks or open flames.
