Ok, so I got a new "used" motor from the junkyard with 136k miles on it. Put new rod bearings and new main bearings, new oil pan gasket, high volume oil pump, new intake gaskets. pretty much made sure the motor would be impervious to any kind of screw ups. We left it idling for a good 30-45 mins and it had really solid oil pressure of 60-70 lbs. Test drove it "around the block" which is a good solid 5-10 miles. Bring it back to the shop and everything is still A-OK. On the way home after 30 mins more of idling, about 6 miles in my oil pressure starts to drop, goes to 40 lbs (which is normal) then it starts to fall even lower to about 15 lbs and my idling rpms start to fluctuate, im about 3 miles left from my house and it i hear either a ticking or a knocking noise (i cant differentiate from either of them, sorry) and the oil pressure now goes to 0lbs and when im accelerating it does not go above 20lbs. The sound i can describe as is shuffling cards. the ta-ta-ta-ta-ta kinda noise rofl. Well I barely make it home and I got a drop of oil on the driveway, but I assure you we have covered anything that could be leaking. Anyone have any thoughts on this? I really hate to spend time and money into a motor and not have it run correctly. Maybe the tech messed up somewhere? I'm having the car towed to my shop pretty soon this morning and we can lift it up and take a look. maybe something came loose is my best option right now and im hoping thats all it is. Thanks guys.

 

UPDATE: Got the car to the shop this morning and on a cold start, the motor starts up fine and sounds good like nothing even happened. Only after the car was driven awhile is when it acted up. Could it be a bad oil pressure sensor? Im puzzled and dont know where to start.

 

If you're confident it's running normally, you can remove one of the valve covers to verify you are getting oil pressure to the top of the engine. When you started this morning, did the oil pressure look normal on your gauge or is it still at zero?

 

Well, it could be a few things...but with everything you put into it I doubt it could be some of these, but it is worth a shot.
1) Make sure it has enough oil. The engine may be burning a crap ton of oil or leaking somewhere (indicated by the drop of oil on the driveway)
2) Is the oil the correct viscosity? (normally 5W-30 for all season driving) Too thin of oil can cause low pressure in warmer driving conditions.
3) Is the oil pump screen clean? If the screen is dirty then it can cause a drop in pressure.
4) Is the oil filter used or old? A plugged filter can cause low oil presser just the same as the pump screen.

I also found this website Engine Knock & Oil Pressure Auto Repair Advice that covers these things and a few others in more detail. Hope this helps you out!

 

Just got an update...the motor is knocking on the top-end. when it got to the shop i re-checked oil levels and it was at the "Add" marker. I use 5w-50 Castrol Syntec with a quart of lucas. Brand new screen, pump, filter and all of that. I think what might have happened is with the high volume pump we didn't add extra oil to compensate for the volume of oil that was going through...so I came to the conclusion I lost another motor due to failure to add enough oil? Just a suggestion...I start it up and it has fine oil pressure, just when I drive it home yesterday I drove it 3 miles when the oil pressure hit 0lbs. SO I probably caused the knocking, by driving it that far with no pressure.

Edit: The knocking isn't even very loud.

 

I was told by the machinist who cleaned and honed my block not to use a high volume oil pump without a larger capacity oil pan because it takes some time for the oil to flow back down to the pan.

Don't get discouraged if you have to do more work to it... I had the block honed, I put in new bearings, rings, gaskets, lapped the valves, took apart and reassembled each lifter to clean them all out...after starting it up the first time I had a clacking from the bottom end. Turns out I had a bad wrist pin on one piston, so I had to pull the engine again and tear it half apart to replace one piston!

Did the junkyard give you a warranty on the engine? If you get another, I would definitely use a standard oil pump.

 

Ended up getting a re-manufactured 3year/100,000 mile warranty engine from Jasper. Lets see how this goes lol.