still having oil press drop

[godheadcustoms]

I've been fighting this problem for a while now... I had a pan leak, so I figured as long as I have the pan down, I'll change the oil pump as well. Before I put the pump in I checked the clearances on the pump (fine), #1 main (good w/slight wear), and #6 main (good again). At the same time I also installed a new VDO mech oil press gauge. I fire up the car, no leaks everything's fine, 45-50 psi @1000rpms cold. Here's the problem: when it's hot and on the road oil pressure drops with vacuum. At first I thought it was from RPM, but further testing nixed that idea. What happens is, if I step on the gas, oil press drops by 10psi or so; let off the gas comes right back up. Even if I'm at a light cruise, then let off oil press comes back up. It can be a change of only 25-50 RPM, but press will IMMEDIATELY come back up due to sudden high vacuum(?). Has anyone had a similar experience or any thoughts?

 

[Lazy JW]

I've known of this happening on tractor engines. Try temporarily removing the pcv valve and/or the filler cap to prevent engine vacuum from evacuating the crankcase and see what happens.
Joe

 

[godheadcustoms]

Thanks Lazy JW, I'll try that. This one has had me stumped. So many things were changed at once and I didn't have the gauge in before, so I don't know what the "baseline" was. But it still runs great, no knock or lifter rattle from low oil pressure, just the pressure drop. Brand new pcv valve BTW. Any other ideas?