1991 GMC Sonoma Hall effect sensor

Sensor location varies-refer to repair manual or you can download it here see the bottom of your post or at my signature block

In some EFI system-The camshaft sensor is use to synchronize the injectors the computer has to get the signal in order to energize the injector/s solenoid-check whether they clicking while cranking it. Or use a noid light if its MPFI system

On EFI-equipped engines, fuel pressure in the line does not necessarily mean the fuel is being injected into the engine. Listen for clicking or buzzing that would indicate the injectors are working. No noise? Check for voltage and ground at the injectors. A defective ECM may not be driving the injectors, or the EFI power supply relay may have called it quits.