Treb
Treb Reader
2/18/12 6:19 p.m.

What does the PCV system on an early 98 (manufactured summer 97) 2.8 Audi A4 look like? Having spent all day under the berkeleying hood, there's not much under there that's like a PCV system.

Through Google I can fond a few references to the fact that the early cars have a different setup, but that's about all I can get. There's a bridge pipe between the fronts of the valve covers, and a y-pipe ("suction pump"?) just above the throttle body. But nothing else that's recognizable from any of the diagrams of PCV setups for this motor. Bentley doesn't show anything at all on the subject.

Making sure the PCV system is working is the suggested first step in fixing oil leaks on these cars... so it would be nice if I could figure out the PCV setup.

Any hints appreciated.

Thanks Matt

former520
former520 Reader
2/18/12 7:41 p.m.

I have had luck with changing that piece out and having a great reduction in oil leaks. I am unsure how it works, but it takes the place of a PVC valve you would find in a valve cover.

Treb
Treb Reader
2/21/12 10:03 p.m.

Diagram of the later version.

There's a diagram on that link, and just about none of it corresponds to my car. (only the contents of the orange box; even the valve covers are different) That's about all I can find, though.

Matt

Treb
Treb Reader
4/30/12 10:06 p.m.

Well, I've taken some stuff apart to see what is there and I've replaced some gaskets and the "suction pump"/y-pipe. And there's a still a pretty decent oil leak or two, and I still can't figure out the PCV system, or if there is one.

Looking at my link in the previous, there's definitely no check valve, no long pcv/pipe combo that winds around the engine bay, and no valve covers with vapor separators.

The engine loses about 1 qt/1000 miles -- that's a rough estimate. The oil is coming out the left side somewhere; I've replaced the valve cover gaskets and the timing chain tensioner gaskets, and those don't appear to have made any difference.

Oil does also appear to dump into the intake at some points as well, with the occasional oil-smoky startup. Lovely.

So: PCV, whatever it is, might not be working, but the one visible part ("suction pump") wasn't the problem.

I'd really rather not do exploratory surgery on the (multi-part, plastic, variable) intake manifold to figure our the PCV... any ideas?

I've thought about a temporary dump to a catch can in the bridge pipe between the cylinder heads, just to see if the problem is really that the PCV isn't. But if I don't know what it's supposed to be doing, then I'm not sure if I might be causing other problems while I'm at it.

Matt

Streetwiseguy
Streetwiseguy SuperDork
4/30/12 10:32 p.m.

PCV is short for positive crankcase ventilation. No Europeans were ever positive about their crankcase ventilation, I'm afraid. Up here in the cold, we've been replacing engines for decades because of it. The current champion is the BMW X5 of the last decade, which will suck all the oil out of the crankcase in less than 5 minutes if the breather freezes. Old Volvos used to take at least 100 miles to throw the crank on the road. Legend talks of a small town halfway between Montreal and Quebec City that did a good business in replacing B20's.

That is all I got. Sorry for the hijack.

02Pilot
02Pilot Reader
5/1/12 7:43 a.m.

Put a vacuum gauge on it and see what's being pulled in the crankcase at idle. Depending on the spec, you may need either a slack tube manometer or a standard vacuum gauge; try the latter first (or better yet, a combination vacuum/pressure gauge, just in case there's pressure building up to be registered).

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