99 F150 4.2l excessive vacuum - engine has 206K miles and has enough vacuum at the oil fill tube to collapse a plastic oil container in seconds. Don't know how there is that much vacuum there. Also at idle and normal temperature the oil pressure goes to zero, OK until it reaches operating temp. Vacuum hose routing seems to be OK. Anyone seen this problem. I have two 1999 4.2Ls and a 2003 4.2l to compare with, this one stumps me.

 

The vacuum will collapse a plastic oil container in seconds with engine running. It'll easily pull on the palm of your hand when you cover it. Don't know how there is that much vacuum there. Vacuum hose routing seems to be OK. I have another 1999 4.2L and a 2003 4.2L to compare with, this one stumps me. PCV rattles when it is shaken. The other two don't have PCV valves in the same place, left front valve cover, and I don't see one in the right cover. I've only had this one about a month and it had been parked for two years. Replaced the fuel pump to get it running.

 

My suggestion is getting a vacuum gauge or minimally using a OBDII scanner to read the MAP pressure. I believe the correct manifold pressure is -4.2" HG. At WOT and under full load it should be -14.8" HG.

 

The engine is vented from one valve cover through the PCV to the intake manifold. Air enters the engine from the engine air intake to the other valve cover. I would check the PCV and both of those lines for an obstruction.

 

Sounds like a wide-open PCV valve. They're supposed to be a calibrated airflow device and shaking them isn't enough of a diagnostic step.

Pull the PCV valve out of the valve cover and verify the vacuum in the valve cover/crankcase goes away. if it does, replace the PCV valve with a new Motorcraft (ONLY!) PCV valve.

While you're at it, check your air filter.

 

Roadie led me to it. This 99 F150 had the PCV in the left front valve cover and an elbow in the right rear valve cover. PCV was in the wrong cover. I have another 99 F150 that I've had since new so its got to be right. I moved it to the right rear cover location and the vacuum at the oil fill is now barely noticeable. Now I can address the no oil pressure at below 1000 RPM. I'm going to try thicker viscosity oil and or STP treatment. If that helps then it must be the crank bearings. Might end up being a parts truck after all.
Thanks to all responders.

 

Connect a real oil pressure gauge to see what the pressure actually is. If the engine isn't knocking I would add thicker oil too to get the pressure up, either that or change the oil pump for a higher volume pump.