Q: Fuel pressure drops

The fuel pressure is held up to the injectors by the fuel pump itself. The pump has a one way check ball built into it. The pump will hold the pressure up to the fuel pressure regulator and the regulator should hold the pressure also.

If one or the other leaks, then the pressure will drop and be hard to start. The way to test to see which one is the cause is to block the fuel return line and see if the pressure goes up and does not drop. If it stays up, then the regulator is bad. If it drops, the fuel pump is bad but after this fix re-check to see if the pressure holds since both components can be bad.

After both are checked, and the engine does start each time after, it seems to run real rich then you may have a leaking injector stuck open. This would show up as black smoke when first started and running rough until the excess fuel is cleared. The regulator or pump is the most common problem. Do not rule out the new pump causing the problem. If you would like to have this diagnosed, a certified technician from YourMechanic can come to your car’s location to inspect your car’s hard starting issue and let you know what should be done.