My Titan wont start up.

Check the fuel pressure and get back to us.

How do u check the fuel pressure?

The only way to check the fuel pressure without finding a test port is to have the trouble codes checked.
There is a specification for fuel pressure, but there is not a designated port to attach a manaul test gauge to. Repair failities and dealerships have special tools to check pressure if there is not a safe testing port. However, you can usuall find somewhere on the fuel rail where you can insert an adapter, which would come with test gauge, to check fuel pressure.
Advance Auto and other large auto parts chains have loaner programs where you can borrow tool including pressure test gauges. You might also buy a Haynes maual as they work around these types of issues for the do it yourselfer and show where a test port can be found.
The normal fuel pressure is, (350kPA at idle).
Otherwise a repair facility should not charge more than a half an hour to give you the code and what it means.
Another item you can test on your own is to check if the fuel pump relay is working. When you turn the ignition switch to the, "ON" position the relay will turn the pump on for 1 second to prime the engine. There is a flexible part of the fuel hose that you can pinch while someone turns the key to the ON position. You will feel the fuel pulse in the line if the relay is starting the pump. If it does not then the relay needs to be replaced. Even if it does, you should still check the fuel pressure.

I reccomend you have the trouble codes checked at a repair facility and have them check the fuel pressure if you are not familiar with fuel injected systems as the fuel pressure is bery high and can be dangerous.