I have 04 f350 with a 6.0L it cranks and has a fuel at the fuel pressure regulator, but will not start. what can i check next?

Check the fuel pressure - sounds like a malfunctioning pressure regulator.

What's the fuel pressure first thing , before starting . Could be check valve inside fuel pump module ,fuel drain's or bleeds off over night , drains back into the fuel take .
Car cranks too long Fast fuel pressure bleed off Faulty regulator Part 2

Usually if cranks good but won't start, you have a helper crank it while you visually check for spark at the spark plugs. If spark everywhere, use a gage and check proper fuel pressure and check fuel injector pulse. I don't know what testing you have done?
As far as the fuel regulator, it depends? If there is a return line, the pressure regulator should be on the fuel rail. If no return line, with mechanical returnless, the regulator may be in a loop close to gas tank. With electronic returnless, everything is in the gas tank. Sorry, I haven't found any pictures?

Fuel pressure regulator is a good place to look. look at the extra injector that enrichens the mixture on a cold engine too.

First crankshaft sensor, also called engine speed sensor, next cam shaft sensor.

What is 3.4.

First check your fuel pressure regulator by pulling the vacuum line off and check for fuel there should not be any.Then start the car and with a pressure gauge hooked up to fuel rail pull the vacuum line off the pressure should rise 5-10 psi if it does'nt replace regulator.Next check the fuel pressure it should be 41-47 with key on and engine off if not within specs replace fuel pump.

On the fuel rail there will ba a fuel pressure regulator. It will have a vacuum hose going to it. Pull off the vacuum hose and see if gas comes out of the nipple on the regulator. If it does than you have a bad fuel pressure regulator. If it doesn't than the next step would be to measure fuel pressure with a fuel pressure gauge.

A bad check valve in the fuel pump can cause the same condition you described. It is commonly reffered to as an "extended crank".

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When you have an engine that is hard to start or the engine takes longer than normal to start, with a fuel injected engine it will normally be caused by a fuel problem. Another problem would be slow cranking of the engine because of a low battery, I would check all of the fuel related problems if the engine seems to crank normally. There are a few things to check. First pull the fuel filter off and wipe it off so you don't get gas in your mouth and try to blow through one of the fuel connections on the filter. If you can't blow through it the filter is pluged and needs to be replaced. A plugged fuel filter can cause hard starting and can also damage your fuel pump. The next thing to do when everything is put back on the car is to check the fuel system for bleed down. You need to locate the fuel pressure test connection on the engine. Connect a fuel pressure gauge to the connection and start the engine, then turn the ignition off. With the engine off the pressure should read and stay between 30psi and 40psi, to be sure of the pressure you will have get the spec's on the engine you have. The main thing you will be looking for is to make sure the pressure doesn't start bleeding down in to direction of zero after a few minutes or maybe even immediately. If you see the pressure start to bleed down you have a problem. There are two problems that normally cause the pressure to bleed down. One is a bad check valve in the fuel pump, the other is a bad fuel pressure regulator. The main thing that happens with a fuel pressure regulator is the diaphram inside starts leaking. When that happens sometimes it will leak fuel into the intake manifold through the vaccuum hose connection to the intake manifold. To check for a fuel leak through the vacuum hose connection, locate the vacuum hose on the fuel pressure regulator and pull the hose from either the manifold connection or from the connection at the fuel reguator. If you see any gas at all the fuel regulator is leaking and must be replaced. If it is a slow leak from the regulator you might have to start the engine with the vacuum hose disconnected and look for a leak from the hose. If you don't find anything wrong with the regulator the next problem area would be fuel pressure bleeding back into the gas tank because of a bad check valve in the fuel pump. If this is the problem the fuel pump would have to be replaced. My first guess as to what is causing your problem would be the fuel pressure regualtor although I would definately want to make sure the fuel filter is not plugged. (Please Note) The fuel pressure regulator is located in the intake manifold area of the engine. The fuel pump is located in the gas tank. The fuel filter is located usually somewhere under the car.

The best way to help find the problem, is to have a fuel pressure test done on it, that will tell if the fuel pump is weak, or the fuel pressure regulator is malfunctioning. If the pressure is low, the fuel pump is weak,
if it is high, the fuel regulator is at fault.