* Fuel pump relay or fuse: Even with a new fuel pump, a faulty relay or blown fuse prevents power from reaching the pump. Check the relay and fuse associated with the fuel pump in the fuse box. These can fail intermittently.
* Fuel pressure regulator: This component regulates fuel pressure in the system. A malfunctioning regulator can cause low pressure after the engine sits for a while, leading to a no-start condition.
* Fuel filter: A clogged fuel filter can restrict fuel flow, especially after the engine has sat for a while, allowing fuel to settle. A new filter is a relatively inexpensive part to replace.
* Fuel leaks: A leak somewhere in the fuel line, including the connection at the new fuel pump, will cause the system to lose pressure overnight. Inspect all fuel lines and connections carefully for leaks.
* Ignition system problems: While less likely given the prompt starting initially, a weak ignition coil or distributor cap (if applicable) could cause starting issues, especially after the engine cools down.
* Security system issue: Some security systems can disable the fuel pump or ignition if they detect a problem. If you have an aftermarket alarm, consider checking that.
* Other issues: The problem might not even be related to the fuel system. Issues with the crank sensor, camshaft sensor, or battery could all contribute to a no-start condition.
Troubleshooting Steps:
1. Check fuses and relays: This is the easiest and first step.
2. Check for fuel pressure: Use a fuel pressure gauge to measure the pressure at the fuel rail. This requires a specific adapter. Compare the reading to the manufacturer's specifications.
3. Inspect fuel lines and connections: Look for any leaks or loose connections.
4. Replace the fuel filter: This is cheap and a common preventative measure.
5. Test the fuel pump relay: While you replaced the pump, the relay could be bad and is likely less expensive to swap out.
If you're not comfortable performing these checks yourself, take the vehicle to a qualified mechanic. They'll have the tools and expertise to diagnose the problem accurately. Providing them with the history (new fuel pump installed, then intermittent starting) will help them pinpoint the cause more quickly.
