Fuel pump won't run unless engine is cranking, but won't start

4.3L , L35(RPO engine)
has 1 fuel pump relay PCM controlled
has 1 fuel pump.oil pressure sensor , too.
not sure at all me what a pulsator might be.Ahh Dampener.
what matters is spark first, it must have spark or the PCM cuts fuel dead on all EFI car. (if the PCM detects spark bad in ANY WAY)
the comes cranking the pump just receiver 12vdc cranking
KEY ON ONLY is only 2sec prime puls best is forget that unless have 2 person to test prime, but cranking matters first.
some new pumps are silent, (like top Bosch) so sounds prove little. today what really matters is PSI pressure cranked,
the PCM brain or the oil pressure switch allow the pump to have power cranked, and running.
that is how to test it, cranked only.

"starting with start fluid,but now it just cranks over ,only."
does this mean starting fluid now fails.?
we check spark at all spark plugs no just 1.
we check oil pressure to, if zero PSI cranked that is bad .
last is fuel pressure if not at spec, it will not start.
spec fuel pressure is 58-64 psi
yes some fuel rails or near by or near tank, have pulsator that is really regulator/dampener.
it prevents old cheap pumps from madly pulsing the rail and causing injectors to mess up. vane pumps do make pulses some worst tan others, (some even by pass it, but there is their call)
Is this a TBI throttle body injection? or MPI.

the SM states this. (it has a 2 second prime for sure)

If the engine does not run, turn the ignition ON, but do not attempt to start the engine. Listen for the fuel pump to run. Within 2 seconds of turning the ignition ON pressure should be 58-64 psi (400-440 kPa) while the pump is running. Once the pump stops, pressure may vary by several pounds, then it should hold steady. If the pressure does not hold steady, wait 10 seconds and repeat this...

I guess you mean it cranks good but won't start? Cranking is starter motor cranking the engine. Make sure battery has a full charge and connections all good. Did you use a gage and check proper fuel pressure, key on engine off? You could try cycling the key on and off several times before you crank it, see if it helps? Another thought is to do a voltage drop test on some of the fuel components, fuel pump--fuel injectors. Engine cranking the systems get battery voltage. Engine running the systems get generator voltage, the gen voltage can be several volts higher than battery. Just a thought.

Is it an 94 or a 2004 Silhouette.You should hear a fuel pump when turning on the key (anytime after the key has been off for about 10 seconds) or whenever there is oil pressure.
If there is no fuel pump sound or fuel pressure when the key is turned on (this is the prime cycle) then crank the engine for at least 10 to 15 seconds to get oil pressure as this is the 2nd source of power to the pump and what powers the pump when driving.
Still no pump running?
Check fuse /wiring/connections/including ground.
Lastly..... New fuel pumps don't always work just because they are new,

This sounds like a fuel system priming issue. When you first turn the key to the ON position (not cranking yet), you should hear a three-to-five second buzzing noise. This is the fuel pump running to pressurize the fuel system for cranking. This is controlled by the PCM and is relay activated. Once the vehicle starts and oil pressure rises, then the fuel pump is activated by the PCM via a different relay. If you can't start at first, what is probably happening is that the prime is not occurring and you have to crank it until the PCM sees oil pressure and then fires off the fuel pump. It could be PCM wiring or a bad fuel pump prime relay.

Hello there , sounds like your fuel pressure is low , your fuel sensor may be faulty or your fuel pump is sucking air from between the pump a fuel tank .. Regards Graham ...

Yes, it should. If it is conventional (like other GM cars), the pump will turn on for a couple of seconds when key is turned to on. This will prime the system for starting. When key is turned to start (cranking), the pump is turned on again at the relay, and pump stays on as long as cranking the engine happens. Once engine is started, the oil pressure switch keeps the pump running.
The best way to check if pump is good is to use a fuel pressure gauge. If it does not have a test port called a Schrader valve on the fuel rail, the pressure gauge must be teed in somewhere convenient. But if you take off the line at the filter, some gas should come out with key on, and when cranking the engine gas should come out in a steady stream.

Have you checked the "Bump Switch" this is a small inertia switch which turns offf the fuel pump to prevent it running in the event of an accident. They are usually mounted in the boot(trunk/load area) . There should also be one mounted under the front of the vehicle to initiate the Airbags. They usually cut the earh return(at least it does on my Granada, XR3i and Sierra XR4x4) hope this helps.

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.

Think the oil pressure switch keeps the fuel pump running once started. Suggest replacing Oil pressure switch. And no it won't effect oil pressure reading when it goes bad. The switch is a safety device. When you roll it over and the oil pressure drops the switch cuts off the fuel pump. Neat huh? Need some good feedback Thanks!

The s10 have a fuel shut off relay to shut off fuel supply in case of an accident. They also have a anti-theft system that prevents fuel in case of theft.Pull the fuel line off and crank the engine to see if you get fuel. Sorry I can't be of more help but without hands on vehicle it is hard to tell.Also your fuel pump maybe sounding like it is pumping. In other words it may be running but not pumping fuel it mat have a ruptured diaphragm in the pump.The pump is running but not pumping fuel. Pull the fuel line off at the fuel filter and turn on ignmition or crank the engine you should have about 50PSI coming out.If you don't install new fuel pump.These vehicles are common for this problem the fuel pump runs but does not pump fuel or not enough pressure these vehicle require 57 PSI to start if it has less than 51PSI it will not start unless you use starting fluid then it will run.It will run with less fuel pressure it will just not start with less than 57PSI.

Hope this helps