Hu, new member here. I recently inherited a 98 c2500 with the 5.7 from a friend that passed. It has been sitting for a few months. When I try to start it it cranks but will not start. I checked for spark, and it has it. It will run for a few seconds using starter fluid then dies. I replaced fuel filter, checked relay and checked pressure with Guage at the test fitting on top of engine. When I turn key to start position I get about 5psi. If I continue to do this, waiting 5 seconds before cycling key it will build up to about 62psi but it takes many times to do this. It will then start but only run for a few seconds. My next thought is fuel pump or pressure regulator.
any help or suggestions would be greatly appreciated, thanks.

 

Sounds to me like you have a weak fuel pump. You should have about 60/65 psi on the gauge. I have already replaced the fuel pump on my 94 chevy 5.7L truck twice.

 

I tend to agree with Birdman01's assessment. You likely have a weak fuel pump. 58-to 62 PSI is ideal fuel pressures.