Why is my car having trouble starting after having the fuel pump replaced?

they usually don' t mess up on that part. However check your fuel filter it might not be working causin the pump to not receive fuel. Or have the pump re changed

What kind of car is it? Electric fuel pumps behave differently from manual ones. I'm wondering if the fuel pump they installed was low quality and would take a few seconds to build up pressure (or leaking somewhere). Electric pumps should start without pumping the gas, if you pump it it may cause a delay.

If the timing was off it would take a few seconds to start also.

have you had it tuned up in awhile? does it take longer to start that before the fuel pump?its kind of hard to tell if the fuel pump ( shorted out ) unless the fuel tank is removed and the pump dissembled, ( to check the wires /motor ) or having it hooked up to a diagnostic computer ,otherwise its a guess,or they installed the wrong pump,and your not getting the proper fuel pressure ( have that checked ) wlh1us

The output pressure of fuel pump is important for starting(also driving).

if your car doesnt has a return fuel pipe from fuel rail(on engine) then it means the output pressure of pump, fixed by a regulator on fuel pump assembly.

check the pressure of old and new regulators. normally it is wrote on them(it would be about 3 bar). it means the fuel pumps output press. is higher(about 6 bar).

try this out. turn your keys on and off about three times before you start it. this will prime your fuel system. then try to crank it. if it instantly starts, then you know that your fuel is draining back into the tank after you turn your car off. some fuel pumps/systems have a built in check valve that is supposed to prevent this.

Some of these shops fix one thing and break another. In testing or diagnosing, They may have removed or changed your ignition rotor or stem. These are hard to realign when moved and cause delay in ignition timing. You should return to shop and explain to them the symptoms. It may be obvious to them what has gone wrong.

3 to 4 seconds of cranking isn`t un reasonble with most cars.

This would be normal, for the amount of time for it to crank and start.