Starting my grandpas truck that has been sitting.
 

Hey Whats up - This is my first post. I am not much of a mechanic, I am a general contractor. So please don't respond to my post like I am a stupid asshole. My Grandpa died many years back, he had a 91 silverado. 5.7 liter, it has 115,000 miles. It is very clean, except for the ****ty chevy paint that is flaking off as usual. Well, my uncle let this truck sit for like 4 or 5 years, and I just recently bought it from him. He said it was running good up until the time he parked it. I bought a new battery, and put some gas additive in and some fresh gas,(it had like an 1/8 of a tank). I tried starting a few times, but no luck. Can someone tell me what would be the correct process of trying to start the truck? Also, it has EFI. I am not sure if that is a carburetor or what? But Should I drop gas or starter fluid in it or not. i don't want to do something stupid. If thought I would give it a try before towing it to a mechanic (which it obviously will need).

Sitting that long, the fuel has pretty much gone to crap. You'll need to drop the tank, drain it and get fresh fuel in it before you can start diagnosing any other potential problems.

New gas, check plugs, wires, cap and rotor. When you pull the plugs put about a teaspoon of oil down each cylinder this will help reseal the rings and build initial compression.

Personally, I'd put a shot of ether down the throttle body after adding the oil and checking everything like red02 said. Chances are very high that your fuel is garbage, but if you get enough fresh fuel in there ......... it might just start and run.

My guess is that your injectors are clogged badly. Try removing the air cleaner and looking at the throttle body injector area down by the throttle valve and see if it squirts fuel when your assistant cranks the engine.