Higher than Normal Negative Crankcase Pressure

[walster57]

Up until recently my 2016 Fiesta's crankcase pressure on the accessport has ranged from -0.26 to 0.05 on WOT pulls up to redline. Now on WOT pulls as the RPMs approach redline, the negative crankcase pressure increases to -0.40 (is this crankcase vacuum?). I've had Radium oil catch cans on both sides for 5+ years no issues at all; the PCV side can goes 20k+ miles and barely fills up to the halfway point, while crankcase side has caught zero oil since I installed it. Randy tune from Mountune at least 6 years old now, about 115k miles on the engine, tuned since 40k miles and owned this car since new. Original turbo but nearly every other bolt-in installed. No check engine lights. I installed the UPR check valve on the PCV side with no change. All hoses and connections look great and snug, and the hoses don't appear to be collapsing. I haven't done a smoke test or compression test yet because I'm afraid of the potential results. Car still pulls fine otherwise and accessport shows normal HP/torque numbers. Zero oil loss over 5k mile oil change intervals, no smoke out the back.

I'm not really understanding the PCV explanations online (like Dizzy Tuning's) and what negative crankcase pressure or vacuum really means (again no idea what I'm talking about). I was hoping someone could please explain like I am 5 years old the possibilities as to what could be causing this increased vacuum. Are my piston rings one foot out the door? Turbo seals failing? Something restricting the PCV? Intake valves need cleaned? Intake manifold gasket? I saw a forum post about old Radium hoses collapsing and I was thinking that could increase the vacuum pressure, but I thought I had the revised hoses. Again though I'm having trouble figuring out how to troubleshoot this.

Thank you dudes for any info at all!

 

[Intuit]

Think of your "crankcase" as your oil pan.

An explosion ignites in each cylinder, pushing its respective piston down toward the oil pan.
Ideally and (somewhat) for maximum efficiency, we want all of the gas from that explosion to be pushed out through the exhaust valve at the top of the cylinder.

But what really happens and more so as an engine wears, is some of that exhaust ends up in the oil pan; having got passed the piston rings a.k.a. "blow-by".

Before EPA regulations, it was okay to just vent the oil pan or "crankcase" into the open air.
With EPA regulations, this exhaust (containing unburned fuel, carbon monoxide, oil vapor from the pan and other undesirables) is sent back through the air intake where it'll reenter the cylinders for another round.

This results with a net-zero release of untreated exhaust.

Having pressure build up from blow-by would be indicative a problem with either crankcase ventilation (PCV) or/and a worn-out/neglected/abused/defective engine.

Having negative pressure means there's not enough blow-by to keep up with the crankcase ventilation (PCV). I'd think that be a positive thing. But I suppose it could also mean that the engine is being starved at the intake; clogged air filter for example.