OK so I have a 95 formula 355 lt1 fresh rebuild all brand new parts. At idle on start up it has 40psi oil pressure I can let it idle 30 minutes and it doesn't move. I take it out for a drive and it looses oil pressure between shifting gears. So I stop let it idle for a second reads 0psi so I kill it. I check oil normal level doesn't smell like fuel doesn't have any shavings in it that I could see. Let it sit 10 minutes start it has 40psi again drive it home and looses oil pressure in drive way shut down. So I drain the oil no metal I can see put 10w30 castrol back in it start it up has 40psi at idle again drive it losses oil pressure after driving again so I stop let it sit and throw a mechanical gauge on it and start it the dash gauge say 40psi and the mechanical say 75psi . it wasn't a gauge I could leave Hooked up so that disconnected it drove it home and oil pressure did the same thing??? Very confused and it has a new oil pressure sending unit so it shouldn't be that. Scared I've got 5grand wrapped up in this motor and I can't afford to spend anymore sorry in advance for my writing skills using a cellphone

 

your pressure gauge may be suspect..

however I would confirm your pick up tube did not come off the oil pump. probe with something in oil drain hole and see if you can confirm it is on.

also did you re-use the stock oil drive shaft/plastic collar?

 

Replaced shaft with new one but it came with the plastic collar.
Will check oil pickup tube this weekend

As far as it being the gauge it is a good possibility the car sat since 07 before i built my car so I ordered a separate oil gauge to verify while driving

 

Did you reinstall the stock windage tray? Are you possibly over-filling the oil?

 

Yes windage tray is stock and installed. I don't believe I'm over filling it just 5qts and its reading on the dipstick where its supposed to

 

Sure sounds like its cavitating. What oil pump did you use?

 

New mellings standard volume pump

 

have you determined if your pick up tube did not fall off?

 

As far as I can tell pick up is still on

 

What diameter is the pickup tube? Did you space the pickup screen correctly off the bottom of the pan? Did you install drainback tubes?

Have you installed the aftermarket pressure gauge?

I recall someone posting a picture recently of the teeth worn off the pump drive shaft. He had cracked the plastic retainer by over-torquing it while installing.

 

I went to the Melling IS-55E oil pump drive shaft($8.99 at autozone). Gets rid of the plastic collar. When I pulled my engine apart for the CC503 install, the plastic collar was intact, but shattered when I tried to moved it.

Torquing that oil pump drive gear stub to the proper value is very important as well.

Was the engine cold on startup with the mechanical gauge? The 75psi sounds more reasonable on cold startup than 40psi. I get 70+psi on a cold startup with the high pressure spring and a std volume oil pump.

If you can spare the cash, I'd grab a new AC Delco oil pressure sending unit. When I last checked my oil pressure reading against a mechanical gauge, they were very close in the displayed reading. Certainly not 30+psi apart. I think that's reason enough to buy a new one. Especially if the reading was fine before the build(meaning the needle in the cluster had no known problems).

There is a special socket to install them...be careful. I broke a new sending unit when torquing it down. Snapped it off in the socket.

Just a little background on my own oil pressure issues. I understand your concern as I had oil pressure problems after I started upgrading as well. Not like what you have, but a dip in pressure on the 1-2 shift from 3000-5000 rpm. Pressure would drop 10-15psi then come back. Made me very nervous to see that when the revs are going up to 6000+.

A canton pickup(20-013) and moroso oil pan(20185) solved that issue. I think the pickup did it more than the pan, but since I did both at the same time I can't say which it was.....

Before fix:
After fix:

 

OK the mechanical oil pressure was after driving 2 miles to my shop. So it wasn't all the way cold. And as far as sending unit I very well could have gotten a bad one its a Borg worner from O'Reillys I've never had issues with them before but it could happen. Still waiting on gauge to come in