What type of hose can i use to repair the fuel lines on my 1999 chevy silverado ls

if it is a common rail model the pressure will be in excess of 25.000 psi
Best have an accredited diesel specialist shop check it out as pressures that high require special gauges and a lot of knowledge of the handling risks

Throttle body injection I assume , watch butterfly on injector and c if it injects fuel , if it starts w ether but shuts off its still not getting fuel into cylenders and since your fuel pressure to engine is normal , the problem is in the throttle body or injection ..possible electrical ...if for some reason u still have a carbureted engine hit me back up it could be sumin diff

This sounds like fuel injection, is it? Or I think you would have said if it was a carburetor. But if fuel injection, it is the pump and the fuel filter's job to put fuel under pressure in the lines and up to the engine, or really to the injectors. If you have fuel pressure in the line, then you have fuel pressure to the injectors. (If not, check the fuel filter.) And then, it is the injector circuit's job to put the fuel into the cylinders.

Just first be sure the fuel pressure is correct. For throttle body injection, that resembles a carburetor somewhat-the injectors are in the throat, the required pressure is usually around 13-20 psi. But if you have multi-port injection, the pressure requirement is much higher, usually 40 psi or more, sometimes as much as 60 psi. If it is carbureted, though, it takes very low pressure, 5-7 psi, and you would need to check if the gas is actually getting inside the carb and filling the fuel bowl inside.

But back to the injector circuit: every injector has only two wires to it: a power wire and a ground wire. The power wire is constant voltage to the injector as long as the key is in run, or on, or in start. The injector is an electrical solenoid, and it gets the power on one side, and when the ground wire is grounded internally in the engine computer, the solenoid is energized, a fuel passage opens, and the injector sprays fuel out. This is called the injector pulse, it only happens for a split second. But you see why the injector must have fuel under correct pressure to shoot the right amount of gas into the engine. You can check the injector circuit, both power side and ground side, with just a simple test light. Post back if you want that, I can give you the procedure. Good luck, and probably good night.

Are you sure it is a carburetor and not throttle body injection? They do look similar.
If it is a carburetor, there would not be a regulator. The fuel pump will either be a mechanical pump mounted on the engine, or a low volume electric pump in the gas line from gas tank to the engine.
If it is throttle body injection (TBI), yes, there is a fuel pressure regulator, probably located near the throttle body. It will have gas lines connected to it (one line will be a return line back to the gas tank) and a vacuum line. The fuel pressure on TBI systems is not as high as multi point injection, usually around 20 psi. You would have to check the specific pressure requirement for your pathfinder.

Take off the air cleaner cover and look at top of unit. A carburetor should have a choke plate right at top of the carb throat. However some Nissans by '88 had a carburetor without a choke-it used an enricher jet controlled by the ecu for added fuel when starting.. On a TBI, looking down at the unit where the air goes in, you will see one or two injectors with a wiring harness connected to them-each injector will have two wires connected to it.
If still unsure, check engine designation on the under hood label. Carbureted engines will have a s letter designation, injected engines will have letter i. To explain: my '87 Sentra is carbureted, so engine designation is E16s, some same engines were injected, so their designation is E16i.