Q: 2003 altima will not start after replacing CPS, checking spark and replacing fuel pump

Whether the fuel pump is new or old, the pressure has to be tested on the fuel rail to be sure the pump, and other fuel system components such as the filter, regulator, etc., are actually working. If the fuel injectors are not working, even with good fuel pressure the car will not start so injector operation has to be verified, too. If the engine cranks at adequate RPM, be sure there is adequate fuel in the fuel tank and that the fuel is not old. Download any OBD-II trouble codes that have been stored and examine those codes for diagnostic clues. Basically, if the starter motor is turning the engine over rapidly, at sufficient RPM, but the engine does not catch and run, that means that there is an ignition, fuel, air induction, or mechanical fault in the engine that will have to be repaired. Check for vacuum leaks, an air induction fault like a stuck idle air control valve or, considering fuel, check for a failed temperature sensor that must be working properly to signal the PCM to enrich the mixture on cold start. Other possible no start faults are low compression, defective spark plugs, a defective coil(s) and a broken timing chain. Regardless of the underlying cause, if you request a no start diagnostic the responding certified mechanic will get the problem diagnosed and repaired for you promptly. Please let us know if you have further concerns or questions as we are always here to help you.