So I have a weird problem. With the oil cap on the oil disappears from the dipstick. With the cap off there's suction at the oil fill like crazy.ive cked the pvc valve all the hoses and lines.took off the intake manifold and cked the rear hoses. All good.. it has codes 171 and 2197..

 

So what year and engine?

 

Oh Golly. . It's an 05 f150 with triton engine. With the oil cap off and the dipstick out its suckling at the dipstick tube.

 

Which Triton engine? 4.6 or 5.4?

 

5.4

 

Seems to me there should be some suction there because the engine is vented to the intake manifold so blowby can be sucked into the combustion chambers and any gases burned.

 

The 5.4 does not have a PCV valve, there's a fixed orifice in the valve cover.

Suction through the filler cap and dipstick is completely normal, that's how the positive crankcase ventilation is designed to operate.

 

Yeah if I leave the cap on and drive it a awhile it looses oil pressure. You know when the engines running and you pull the dipstick it's covered with oil .but when you pull it with the cap on there's no oil like it's empty. Vacuum is sucking the oil out of the pan. The 5 4 HAS A Siphon Oil pump.

 

You should not have any significant vacuum in the crankcase. Filtered (and "metered") air is drawn from passenger's side of the air box at the throttle body, into the Bank1 Valve Cover. It should 'draft' air through the crankcase - out of the Bank2 Valve Cover (without a PCV/valve) and into the intake manifold.


If you have vacuum in the crankcase - the inlet hose on top of Bank1 V/C must be plugged / clogged.

 

I cleaned out the drivers side valve cover where the elbow pipe goes to it was clogged but air blows thru it now. I switched out the hose on the pass side hose to the valve cover to intake. Air will blow thru both ways . With oil cap off air blow out the little pipe and air blows thru the pipe out the oil fill. Maybe there's debree floating around in the box and it's sucking and blocking the hose. Otherwise I don't understand.

 

THAT is normal. Under that scenario, even with Oil Filler cap on and sealed, you should never have a vacuum build up in the crankcase.