Blazer ran fine, parked and came out after lunch

Hello csdunne: My name is Roger and I will answer your question. The oxygen sensor will not cause a no start condition. How ever the fuel pump will. You need to test the fuel pressure. Whether you have a 4x4 or 4x2 the pressures are the same. Key on engine off. a 4.3 W engine should have 60-66 psi. A 4.3 X engine will have 55-60 psi. I would also check the fuel filter. A dirty fuel filter will cause low fuel pressure. If the pressure is below the min. by just a few pounds the engine would not start. Should you need further help please just ask. Please rate the answer you received. Thank You for using Fix Ya. Roger