As someone who spent a long time diagnosing similar problems I can probably offer som insight. Things to check:

1) PVC System
A plasticish pipe runs over the crankase to a Y adapter between intake 2/3, with a small hose coming off that to the intake manifold and a larger hose going straight down to a plastic unit attached to the block (kinda on a ledge).

Chekc all the hoses for resistance or deposits, using a rag + coat hanger + sweat to clean them out. Pay special attention to the Y plastic unit, teh smalll hose, and teh nipple on the intak emanifold where the small hose connects (use a dril bit on this last one, but be careful not to drop it into the manifold... that would SUCK).

The plastic item down below is the breather box, or oil separator, or PVC unit (whatever). It is RARE that it gets clogged, but it is possible. It's a cheap unit, so you might as well just replace it if you remove it. Easiest way to do that is to unbolt it, push it back towards teh firewall, and drop it down to teh ground (messy to pull it up over teh engine). Make sure you replace teh rubber ring on the bottom of teh new one.

2) Lean Engine
This is, in general, the more common culprit. If you find that, after cleaning the oil spot, it ONLY returns after you try to boost, then this might be the problem. Basically a lean engine runs hot, and the hotter it runs the more pressure it will generate from gases, pre-det, whatever. When you boost you increase this pressure even further, and the excess pressure can push oil past the rings, increasing crankcase pressure and leading to teh oil stain you see on the cover.

Check all the turbo hoses aft of the AMM for leaks. Pay special attention to low spots where oil can pool, connections, hidden areas, etc.

Check the AMM. I recommend just disconnecting and reconnecting it to see if its seated properly as a first step... it may look right and STILL not be connected properly (happened to me).

Check the ECT. This is the engine coolant temp sensor that reports temp to the ECU and controls mixture and injection cycles. The FAQ should have the proper resistance information, etc., or you can just replace it outright (it's cheap).

Check Knock Sensor wiring and sensor. If the KS is faulty it could be leaning the engine unnecessarily, or affecting mixture. It could also be covering another problem by leaning out the engine, but...

Check the CBV. I beleive you have a Mitsu on your 89, so the CBV is on the turbo unit itself. Whethe r and r is possible on that CBV I have no idea, but one quick test is to pull the hose that runs to teh CBV over teh crankase (small vacuum hose) off the intake manifold, wrap your lips around it, suck tight, and plug it with your tongue. If it's working you should be able to hold pressure.

Hope this helps.

good luck,
rt

I had this on my B230ET. Got a new seal, then decoked the breather hoses and oil separator. If you do not know, the oil separator is the plastic box bolted to the engine block with the breather pipe attached to it. You may find that the little gauzy thingy under the air filter is clogged also. Either get a new one, or just throw it away. It's not important.
Bear in mind that if your breathers are like mine were, you'll need a length of wire and plenty of degreaser to unclog the system. It may take a while, but perservere, you'll reap the results.

For starters, flip over the oil cap gasket for a fresher sealing surface, or, just replace it (cheap).

Remember that this is a plastic oil cap, so, the Don Foster "jiggle test" does not apply here -- i.e. your cap will rattle, no matter how good the engine's positive crankccase ventilation.

>I suspected flame trap clogged only to find no actual flame trap instead a >powered valve devise(I don't know what this named) and don't know if it may be >inop. or has anything to do with the oil leaking out of the filler cap.

If yours is a Turbo engine, then no, is does not have a flame trap. It has a plastic "Y" connector just above a "S" hose on top of the black plastic oil separator (box).

>powered valve devise(I don't know what this named)

Don't know what your mean here.... I am not aware of any powered valve on this engine having something to do with the crankcase ventilation. Are you looking at the idle air control valve under the intake manifold/throttle body?

If you suspect high positive crankcase pressure is blowing out the oil, remove and inspect the oil separator box and clean it in a gallon of kerosene to flush out any sludge inside.

Another thing to check: is oil in the throttle body and/or intake air hose coming into it? That would be another clue as to too much crankcase pressure, suggesting a blocked ventilation system somewhere (again, the oil separator and that "Y" connector. Maybe one of its related hoses.)
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1989 740Ti 1986 240DL 1984 244GL