I have a 1998 gmc 4x4 5.7 at. Its been getting harder & harder to start, but went it started it would run great and restart that day. Today it didn't start, so the fuel pump is making nois so that is working, put a new fuel filter on, no help, so I put some gas in the throttle body and it started right up for 20 sec. so I pull the fuel lines going to the fuel meter body and turn on the key, great pressure, but not getting to the engine. So I need help, what to do next?

Hi there, may be you should take a look at the fuel pump if the 4x4 is getting gas when you start iwthout pressing the excelerater then it could be your starter is going.

Have you checked your injector.
Also you should have 30 to 40 pounds of pressure on the full line when the truck is shut off.
Which means if you don't have enough pressure injector doesn't work properly.
Also if you don't have the right pressure it means your fuel pump is going out it just isn't dead yet.

If you have fuel at throttle body but not coming out of injector then you need to check you have 12 volts at injector and that its being switched by ecu to allow fuel out, if you can't here injector clicking then you can dsiconnect it and put 12 volts an a earth to it and it should click, like flash the earth to battery earth and it will clikc every time you do it.

If the injector clicks its working my guess is...

You crankshaft sensor had a weak signal and has got bad enough now that the ecu can't see the engine turning over so will not inject fuel?

Do you have accesss to scope meters etc?