I really need some help here. I have a brand new LS376/480. I have tried 3 gauges (two electrical and one mechanical) and can't get an oil pressure reading. I removed the gauge and cranked the engine and nothing. I removed the oil filter (which was full of oil) and cranked the engine. Not a drop came out. After talking with GM and hearing about some problems with the o-ring and/or the relief valve spring, I dropped the pan. Before going any further, I thought I would zip tie a plastic bag to the pick up tube and give it a couple cranks. It wanted to suck the bag inside out. It looks like the pump is actually working. What do I need to look for? Any help would be greatly appreciated.
I had to pull a plug on the side of the motor(drivers side front)and use a vacuum pump to pull oil through the oil pump to prime it. Once I got oil there it had oil pressure after that. I had previously stuck a oil funnel in the oil pressure port where the oil pressure switch normally goes and gravity fed oil for days thinking it would prime it the other way.
Found the problem. The o-ring on the oil tube pickup was pinched. Luckily, the pinched part didn't break off and I have to fish it out of the system. Per GM, this is a known problem with the LS3 engine. You would think GM would have fixed it by now.
Oil pump o-ring pinching is a known issue with all LS engines.
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Law of Mechanical Repair, After your hands become coated with grease, your nose will begin to itch and you'll have to pee.
Law of Probability, The probability of being watched is directly proportional to the stupidity of your act.
LS3 418, 248/254 615/595 with XER and XE lobes. AFR 225, 1 7/8 Hedman headers from BRP. 200-4R. 9" Ford rear with 3:50 gears.
LS3 Crate Engine with no oil pressure 
