I have a 96 EX with F22B1 V-Tec engine that has 245k miles on it.

The engine has had a chonic oil seepage problem since I bought it three years ago (with 228k miles, so we haven't drive it much). I've replaced most of the rubber gaskets, and have done the timing belt/pulley/seals job about a year ago. I am in the middle of an oil pan gasket change to get the last of the oil leaks.

Problem is, I get a lot of positive air pressure coming out of the oil filler hole whenever I take the cap off. They say you should have no air movement or slight suction out of that filler hole. On my car it blows pretty strongly. The air is completely clear, no traces of smoke.

And I know if I don't solve this positive crankcase pressure problem, chances are the engine will continue to leak oil as it will be pushed out of any rubber seam it can find.

Things I've checked:

* compression check: 165-165-165-165. This seems to be very good compression considering the age of the engine ... no cylinder is low. So I would assume that rings and valve seats are not allowing blowby.

* PCV valve: I replaced this a year or so ago with a Honda OEM PCV, along with the hose that goes from the PCV to the intake manifold When I pull the PCV off the valve cover and feel the bottom opening, it sucks pretty strongly. So I am thinking that the PCV is okay -- it's just not alble to pull as much air as is coming out of the crankcase.

So what's left that can be causing all of that positive air flow? All I can think of is (a) worn exhaust valve guides and/or partially blocked exhaust.

One other thing I've noticed about the car -- it doesn't seem to like to rev easily past 3500-4k rpm. I will go above 5k if I really step on the gas, but not sure if something is holding the engine back from freely hitting the high rpms ... and if that is related to the positive crankcase pressure issue.

Any ideas on what to look at next?

Thanks. John

 

My next step would be to test for a clog in the exhaust. A vacuum gauge on the intake could hint towards a clogged exhaust. Getting a pressure gauge on the exhaust is another route, but tricky to do. You may want to remove the cat and see if the back pressure goes away. This will be very loud, so get some ear plugs.

EDIT:You should also disconnect the exhaust after the converter (with the converter still attached) to rule out a clog past the converter.

For engine valve issues, I would do a leak down test. That is a pretty definitive test for leaks in the valves, rings, or head gasket.

 

Sorry, I forgot to mention -- I hooked up my ODB2 reader and went for a drive to monitor whatever engine vitals I could ... Manifold Absolute Pressure (MAP) measured 6-8Hg at idle, and low to high 20's under hard acceleration. So I think this means there is a proper vacuum on the intake side? Does this rule out a potentially clogged exhaust?

Yeah, I hesitate to do this in my residential neighborhood. However maybe a "test pipe" to replace the cat ... that should test for cat failure and still give me a quiet exhaust operation.

yes, that makes sense to try as well. It would be nice if I could find a donor car somewhere to grab the exhaust system from.

Can a leak down test find problems that a compression test misses? WIth a compression of 165 on all four cylinders (vs factory spec of 178) I though would indicate there are no significant leaks in the rings, valve seats or head gasket. Am I wrong?

Thanks. John

 

Okay, I just finished my oil pan gasket replacement this morning, fired up the engine and took this video:


What do you think? Blocked exhaust?

 

I recommend pressurizing each cylinder to 100psi one at a time at TDC for each cylinder. Let each sit for at least thirty minutes and while doing so listen to the exhaust and intake manifold for a hissing sounds which will indicate a leak. There should be little to no pressure drop in each cylinder unless there is a leak in the connection fitting(s).

 

A leak-down test give you more information, because it would indicate the rings, head gasket, intake, or exhaust valves on each cylinder. I think it is worth trying.

A test pipe may be the way to go to keep the engine quiet. I'm not sure what a normal map reading is for your car. Search the web to find out how the vacuum responds to a clogged exhaust.

 

I guess if I can find the equipment to do a leak-down, it can't hurt to get more data. My issue is that this car is not worth doing a valve job, and definitely not pistons and rings. And with the compression test as high as it is, I figure it's not in that bad of shape even if there is leakage. I would just have the kids drive the car as-is for a few more years and then pass it along to the next family with teen drivers

replacing a clogged cat is something I would do, since it's a simple DIY replacement procedure and there are aftermarket cats available at a somewhat reasonable cost (or pick up a used one somewhere)

I looked around for info on manifold vacuum but couldn't find anything informative. There are some videos pointing on bad cats though, that seem to match my symptoms.

 

Hold 100psi of pressure for a half-hour? Hmmm, I don't think even a brand new engine can hold that much pressure for that long.

 

I read at least one online how-to that suggested the engine should be able to hold pressure for 1/2 to 1 hour.

However other blogs tell you that would be 0% leakage, which is impossible. Normal leakage should be under 20%, and for non-specialty engines more like in the 10-15% range, which is supposed to be acceptable. Ex: http://www.hotrod.com/how-to/engine/...akdown-tester/ and https://mobiloil.com/en/article/car-...-leakdown-test

Based on how the leakdown testers are supposed to work, if you stopped introducing air pressure and there is >0% leakage, the cylinder should lose all of it's pressure within a matter of seconds. Or am I missing something?

 

Disclaimer: I've never used a leak-down tester; however, I'm really-REALLY having a difficult time believing a healthy cylinder can hold 100psi of pressure for even a few minutes without a measureable loss in pressure. If they can, then why the need for crank case ventilation at all?