Turns over, but why doesn't it start?

check for power at the fuel pump if no power check relay's fuses ect If you have power at the pump then most likely bad fuel pump.And yes they do quit just like that

You should never try a pump without it being in fuel. It uses fuel for lubrication when it is running. If the vehicle doesn't start at all when you first crank it over it is not the oil pressure sender. If you just put the pump in you might want to turn the key off and on several times to cycle the pump then try to start it. If it doesn't start then check fuel filter or check fuel pressure at fuel rail in engine compartment. Is fuel pump cycling at all when the key is turned on? There is a problem with ignition switches on some of these blazers.

well, you've identified a fuel problem, for sure. Next step is to see if it's getting up to engine. Turn the key on and you should hear your pump run for about 3 seconds, before it shuts off. If it runs, consider if you need a fuel filter, then have the pressure checked.
If it doesn't come on, maybe a fuse is burnt out, a bad fuel pump relay, wiring, or a bad pump. Start by checking for power at pump when cranking with a test light or voltmeter. Good luck.

I would change the fuel filter, because that could cause all those things. Those are the warning signs that your fuel filter gives you when it is getting clogged up.

BUT it could also be an indication that your fuel pump doesn't have the pressure it should have or that you need a tune up (pay attention to the condition of each spark plug when you remove them to give you an idea of what shape your cylinder and plug wire are in). NOTE: Oil coated spark plugs unusally show that cyclinder rings are failing; wet - fuel coated - wires or cap failure>

any codes

If you can't pull the codes from the pcm it has either died or lost it's ground assuming it has power. I would try to get a wiring diagram and check both the power and the ground for the computer itself, because it is what turns on the pump and the wait to start light.

sounds like a fuel pump or filter problem. replace filter first its cheaper than a fuel pump.my fuel filter on my 01 530 was under the driver side half way back along the bottom rail of the car.i had to remove the aero plastic with a plug puller that gave me acess to it.try and replace that first. if it doesn work its prob.fuel pump.

Did you replace the fuel filter along with the fuel pump? You may have damaged the low fuel indicator when replacing the pump but as you stated, the main issue is a no start condition. Make sure that the ground wire for the pump is screwed down tight on a clean surface and make sure the wire and connector is good. It is the wire connected to one of the four screws that hold down the access plate (under the carpet behind the rear seat) to the fuel pump. Also, check the seal around the plate that is held in by the small screws(12 or 15 of them). Check for loose screws. Replace the fuel filter and remove the inlet side toward the rear. Fasten the line into a 2 litre soda bottle then crank the engine and watch to see if gas is coming out of the line. If no, you may have a new faulty pump. Hope that helps.

Ignition key needs programing or its faulty.A

faulty Key disarms the immobilizer for about 2 seconds then shuts down the engine

You must use 5/30 fully synth oil and i guess if you did that and still wont go its going to be air so pump away a bit longer on the primer .Should be some pressure there when its ready to go .