Removing my oil cap with engine idling, it vented a lot of air when I released it and was under pressure. Idle speed also started increasing. I also have a lot of oil on top of the valve cover around the connection for the hose that runs to the turbo Inlet and that tube as well as the entire intake downstream of it is pretty wet with oil.

Bentley manual says the increased pressure would be a sign of clogged crankcase ventilation. I've found plenty of posts here about fixing the opposite scenario with a new valve cover or PCV diaphragm but not unclogging one. Is there a good way to clean it out?

 

wow, nobody?

I also checked my codes this morning and after removing the oil cap for just ten seconds I had "pending" codes about downstream throttle unmonitored air (P1497) and one about idle control.

I guess to ask my question a different way - is there anything OTHER than a clogged up valve cover that would cause crankcase pressure to be trapped? I'm ready to pull the trigger on ordering a valve cover, OCC, and the plugs to eliminate the passenger side PCV hose but without understanding the system a little better I feel like I'm just throwing parts at it.

 

N14 PCV system relies on the intake manifold to draw air out of the crankcase, thus relieving pressure build-up. "Downstream throttle unmonitored air" implies your getting excess air from someplace. Maybe remove and inspect the passenger side PCV hose? "Glogged" crankcase ventilation is pretty vague. More than likely there's a damaged diaphragm, preventing proper operation. I've not read of anyone restoring a PCV system by cleaning it.

A dual OCC system is my choice over plugging the passenger side hose. This is controversial, as others have had good luck plugging it. Just as many, if not more have had grief plugging this hose --- your choice.

 

Thanks for responding - "clogged" is pretty vague, I agree. Bentley manual is good for work, but leaves something to be desired when it comes to describing intended function and diagnosis procedure.

Also note that the codes were only triggered by idling for a short time with the oil cap off - so I'm fairly certain the oil cap off was the source of unmonitored air.

My understanding: Passenger side hose vents crankcase during idle and decel when manifold vacuum is present. When under load/boost, there is not enough vacuum to open the diaphragm and the crankcase ventilation is instead done through the driver side hose to the turbo inlet, with a check valve in the valve cover to make sure the manifold doesn't suck air all the way through from the turbo inlet.

For there to be positive crankcase pressure to release when the cap is open tells me that something has gone wrong with the PCV system so that it can't vent out to either the manifold OR the intake tube. What's weird to me is the code I got when the oil cap was off refers to "downstream throttle" which seems to imply that it was sucking air through the cap and the passenger side hose into the manifold, but if that's the case why was air BLOWING out of the opening instead of sucking in???

I just want to make sure I'm not missing something before I drop the coin on what will be at least the second replacement valve cover this car has seen.

My wife and I are trying to save up for a house and this car was supposed to be a fun gas saver over my Toyota 4Runner. Instead I've spent enough on parts and tools to work on it that it'll take me a least a year in gas savings to pay for it and I've spent more time in the garage repairing it in 6 weeks of ownership than I did on three vehicles in the previous year.

 

I don't claim to understand PCV air flow under all conditions, so I'm not going to be much help. I've had to add another check valve in the passenger side hose to prevent my excess boost (30PSI) from blowing out the PCV system, so I've had my share of self-induced grief. Now that you've described your problem in more detail, maybe someone else can offer legitimate help.

The N14 Mini can be a great gas-saver --- when it runs. I still get almost 40MPG (unless I'm playing), mostly hiway, but I live near the middle of nowhere. I'd recommend that when you get it fixed, trade up to at least an N18 --- easier on marriages.

 

Well I might be crazy, or I just mistook natural puffs of air out of the oil cap opening from the pistons movement for positive pressure. I checked again when I got home from work and paid really close attention this time... It's actually under a very slight vacuum. enough that I can hear a hiss when I open the cap but I can easily remove the cap with only a slight amount of resistance... Definitely within the bounds of what it's supposed to be. So I guess this was all for nothing and I probably saved a couple hundred bucks on a valve cover, but will still proceed with at least an OCC installation, maybe a double.

 

Simple test for PP in an engine. Take a latex glove and place it where the cap goes, stretch it over the opening. If the glove and fingers inflate, you have positive pressure. investigating PP should start with a cylinder compression test to see if the rings are good and if engine is worth repair.