* Fuel Pump Itself: Even though you tried a new fuel pump, it's possible the new one is faulty (though less likely). Double-check its installation and wiring. Make absolutely sure it's receiving power. A multimeter can test this.
* Fuel Pump Wiring/Connections: Inspect the wiring harness leading to the fuel pump very carefully for any breaks, corrosion, or loose connections. This includes the connections at both the pump and the relay. A small break in the wire can prevent the pump from receiving power.
* In-Tank Fuel Pump Filter: The fuel pump often has a filter built into the unit (or a separate in-tank filter). This filter can become clogged, preventing fuel flow even if the pump is working. You'll likely need to access the fuel tank to inspect or replace this.
* Fuel Pump Fuse: Despite checking relays, there might be a separate fuse dedicated to the fuel pump. Consult your Fiat Punto's owner's manual to locate the fuel pump fuse and check its integrity.
* Fuel Pump Control Module (PCM) or ECU: The PCM or Engine Control Unit is the "brain" of the car. A faulty PCM might not be sending the signal to activate the fuel pump, even if all other components are working. This is a more advanced issue requiring diagnostic tools or a mechanic.
* Crank Position Sensor (CPS): A faulty CPS won't allow the ECU to know the engine's position, which would prevent the ECU from energizing the fuel pump.
* Cam Position Sensor (CMP): Similar to the CPS, a faulty CMP can interfere with the fuel pump's operation.
* Immobilizer System: Some Fiats have an immobilizer system. If the key isn't recognized, the system might prevent the fuel pump from starting. Try a different key if possible.
What to do next:
1. Thoroughly check all wiring: Trace the entire circuit from the relay to the fuel pump, paying close attention to connectors and any points where the wiring might be damaged. Use a multimeter to test for continuity and power at various points along the circuit.
2. Check the fuel pump fuse (if separate): Your owner's manual is crucial here.
3. Consult your owner's manual for the fuel pump access: Find out how to access the fuel pump and its filter (if it's a separate component). Be careful when working around fuel; this is potentially hazardous.
4. Obtain a diagnostic code scan: A mechanic or an OBD-II scanner can read any diagnostic trouble codes (DTCs) stored by the vehicle's computer. This will provide valuable clues about the fault.
If you're not comfortable working on your car's fuel system, it's best to take it to a qualified mechanic. Working with fuel systems requires careful attention to safety.
