* Type of fuel system: Modern fuel injected systems are generally self-bleeding. The fuel pump primes the system automatically when the ignition is turned on. Older carburetor systems often require manual bleeding.
* Location of the fuel pump: If the pump is located within the fuel tank, there's usually less chance of introducing air into the lines compared to pumps located externally.
* Method of replacement: If the replacement process introduced air into the fuel lines, then bleeding may be necessary, regardless of the system type.
* Symptoms: If the engine cranks but doesn't start after the pump replacement, air in the fuel lines is a strong possibility and bleeding may be required.
In short: While many modern systems are self-bleeding, it's not a bad idea to check for and address any air in the lines after a fuel pump replacement. If the car doesn't start or runs poorly after the replacement, you'll almost certainly need to bleed the system, either manually (if your car has a method for this) or by letting the pump prime the system during several ignition cycles. Consult your vehicle's repair manual for specific instructions.
