Chevrolet Repair: 1991 Chevy Suburban 5.7L starting issue, chevy suburban, issue question

Question
QUESTION: Hi, 1991 5.7L suburban turns over but won't start until oil pressure is up to 25psi. I have changed the fuel pump, sending unit, tank, filter, fuel relay on firewall, MAP sensor(it flashed a code), and installed a new oil pressure/fuel pump switch(from chev) (I bypassed the old one and it started right up so I changed it). Now it cranks until pressure is up to 25psi and starts; I took it for a test run of about 20 min. hit some traffic ideled down and it stalled and wouldn't start. Any ideas?

ANSWER: Did you check the oil pressure it's self? It sounds like you may have gotten a bad switch for the oil pressure.

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QUESTION: Installed a mechanical OP gauge read close to the one in the truck. When the engine turns over pressure stays at 0 for a few seconds, begins to rise, starts around 25psi and runs at around 40psi. I did try 2 NAPA switches and then the curent Chevy one. Also read it should start at 4psi??

Answer
That's a tough thing to decide on. It sounds like maybe you have a bad connection on the terminal. But it could be wiring or computer related and that makes it really hard to say. I am unsure at what pressure it should start but it may be 4 psi. I can ask a few of my mechanic buddies and see what they think and let you know. Send let me know everything you did so far so I can give them all the information.