2007 Honda Civic LX having fuel pump issues or perhaps other starting issues?

My 2007 Honda Civic LX 1.8 L is having some issues I believe related to the fuel pump but not sure. We replaced the fuel pump in September of this year, so only 3 months ago, and now the car is having problems starting again. The old fuel pump that was in there somehow shorted out and even melted the wiring harness. This one was properly installed. Yesterday I was out driving around running errands and was driving the car for quite a while, then I went to start it and it took me 4 tries but it finally started. It would turn over but would not start. Early this morning when it was cold the car would not start at all, it was jump started and still nothing. Just the turning over but not starting. Later this afternoon when it was warmer it started just fine first try. Everything electrical in the car works too. Do you think the fuel pump has gone faulty or could it be something else?

Electric fuel pumps are easy enough to test, so I suggest that you do that. After-market auto parts have a higher failure rate than OEM parts. If you installed an inexpensive rebuilt fuel pump, I would be suspicious of it.

The cold sensitivity got my attention. Honda has long had problems with intermittent ignition switches. Your 2007 Civic is not affected by the big recall but it could still be bad. It is easy enough to tell - if the warning lights on the panel don't come on in the run position when it refuses to start, the switch is bad. Only the electrical part has to be changed.

If it passes the test the main relay (fuel pump relay) is the next big suspect. Honda has had problems with those forever.

It sounds like the fuel pup check valve is bad.
First thing in the morning cycle the key to the ON position for 10 seconds and then OFF. Do this 3 times without cranking the motor over. After the third repeat try starting the motor. If it starts right away warranty the fuel pump as the check valve is bad and the fuel lines are losing pressure.

It could be related to fuel pump/system issues again but could be other issues as well such as a faulty IACV (Idle Air Control Valve) or ECT sensor (Engine Coolant Temp) which may not trip a trouble code/CEL light either. Some issues don't trip a trouble code due to defective parts if they have no feedback loop to the PCM.

Given the age of the car, you might need to clean /test the IACV and test the ECT for proper function at various engine temps. The PCM adjusts the IACV opening for proper starting and idle speeds and that is based partially on ECT readings. A cold engine needs a slightly richer fuel mixture than a warmed up engine so if the ECT is sending faulty voltage data to the PCM that the engine warmed up when it's actually cold, then the PCM will adjust the fuel mixtures wrong… Too lean… Which results in a no start or hard start. And if the IACV does not open/adjust properly due to being crudded up/clogged with carbon buildup, that can also cause starting issues. It sounds to me like an ECT issue but could be other things. You can also try pressing the gas pedal down slightly which will open the throttle plate a little to allow more air into the engine if the IACV is having problems… If the car starts with that method, then that is one sign that the IACV may need cleaning or testing/replacement.

Do you hear the fuel pump run briefly when ignition is turned on? You may also need to run a fuel system pressure test when the no-start occurs and check/replace the fuel pump relay… Might be sticking on occasion. Try turning the ignition key on without starting and let the fuel pump run for several seconds… Repeat that a few times and then try starting… If it starts better, then the fuel system may be bleeding off pressure too much when sitting… Might be a bad check valve or pressure regulator, etc.