I have a 2000 Nissan Frontier 3.3 v6.
Experiencing that it won't start without pumping the accelerator several times. I changed the fuel filter, and fuel pump, still experiencing the same problem.
What could be the problem?
Considering that the car is with 99.9% certainty fuel injected as pointed out by Paulster2, and that it starts by pumping the accelerator pedal, it is probably related to idle air control (IAC) valve. A 2000 car might use a traditional form of throttle control and not an electronic one. It means there is a smaller valve, the IAC valve, that bypasses the throttle and the computer controls only the smaller valve.
When you get it started, does it idle well or roughly? If there's any form of roughness in the idle, that would also indicate the IAC valve is the cause.
Note that there are many parts in the IAC system, including ECU, wiring, IAC valve, etc. So although most likely the IAC valve is the culprit, there is theoretical possibility that it could be the wiring. Or a fuse. You did check the fuses, didn't you?
I had this exact same problem, after replacing the alternator belt. Every time I started my truck the belt would squeal and I had to pump the gas to keep the motor running. Last weekend, after months of begging, my husband tightened that squealing belt and now the truck starts the first try without me touching the gas pedal. As of now, that has fixed my hard start problems.