Slow starting due to check valve, or leaky injector?

Steve, What year is your Altima? What makes you think it's your fuel pressure? Have you checked your fuel pump? How bout the vacuum lines leading to the fuel pump regulator? How bout the carbon cannister? Sure it's not a starter problem? Or a faulty ignition switch? Have you tried changing your fuel filter? How bout pulling the fuel pump from the gas tank & checking the fuel pump strainer on the fuel pump to make sure it's not clogged with sediment from the tank. Anyhow, hope it helps. ID

Steve wrote:

A library's Nissan factory manuals or Mitchell manuals are your best sources of information for repair information, especially for something like this, and other manuals may contain only very generic troubleshooting information that may cause you to replace parts unnecessarily.

You say the car needs 3-6 tries before it starts but that moving the key between on and off doesn't help. Which is it?

What was wrong with the ignition that made you think that new parts would help at all? What did each old spark plug look like?

If the engine runs fine after it starts, hot or cold, slow and fast, steady and during acceleration, then the fuel pump and pressure regulator are probably fine, and problem may be a check valve or fuel accumulator designed to maintain fuel pressure even when the engine is turned off. But never replace a part unless it fails testing, and to check pressures you'll need a guage (J.C. Whitney is sometimes much cheaper than anyone else for this type of tool), and to test fuel pressure volume you'll need a marked beaker to see how much it puts out in 30 seconds.