Liquid oil in the exhaust.... and other oddities

[911monty]

Ok so just thinking here and it's later than clock indicates.... I referred to the AOS in the basic term as a pressure regulator which is correct, it is attempting to regulate the crankcase pressure at idle to about neg 4.4" wc. Since the plug is missing on bank 2, the AOS "sees" this as positive pressure in the crankcase and opens in an attempt to draw it down. Since it can't with the hole open then AOS is fully open and ingesting massive quantities of oil to the intake tract. Might be worth getting all plugs back in place and test run.

EDIT: The correct term for the AOS is a diaphragm operated back-pressure regulator.

[Gilles]

great thread !!

Very interesting comments from 911

[maytag]

Originally Posted by 911monty

Ok so just thinking here and it's later than clock indicates.... I referred to the AOS in the basic term as a pressure regulator which is correct, it is attempting to regulate the crankcase pressure at idle to about neg 4.4" wc. Since the plug is missing on bank 2, the AOS "sees" this as positive pressure in the crankcase and opens in an attempt to draw it down. Since it can't with the hole open then AOS is fully open and ingesting massive quantities of oil to the intake tract. Might be worth getting all plugs back in place and test run.

EDIT: The correct term for the AOS is a diaphragm operated back-pressure regulator.

Okay, I like this working theory (thanks, by the way). The only question it leaves unanswered for me immediately, is probably born from not having a full-scope view of the AOS system in it's entirety: if it's wide-open, as you've postulated, why is it ingesting oil and not air? Do I have a drain-back that's blocked somewhere, keeping the "intake" of the AOS fed with oil?

[911monty]

Originally Posted by maytag

Okay, I like this working theory (thanks, by the way). The only question it leaves unanswered for me immediately, is probably born from not having a full-scope view of the AOS system in it's entirety: if it's wide-open, as you've postulated, why is it ingesting oil and not air? Do I have a drain-back that's blocked somewhere, keeping the "intake" of the AOS fed with oil?

Short answer is the AOS is ingesting both. If you look closely at the AOS the bellows at the bottom of the de-mister section is directly attached to bank 1 right over the camshaft drive chain. It is attached to bank 2 through the long convoluted tube that crosses over the engine. Due to pressure drop across that tube the AOS will preferentially draw from bank 1. The million dollar question is why did the plugs blow out of bank 2? Still no answer to did the engine spin backwards, but I'm going to say probably. My theory basically is that one cylinder had recently fired but did not get to exhaust valve open. When the piston reversed, the compression ring lost seal on the piston ring-land and dumped as blowby into the crank case. Excess pressure in the crankcase popped the plugs before it could bleed through that long tube to the AOS which had no where to dump due to loss of vacuum in the intake tract when engine quit running. Pressure then relieved through the first weak point. I don't have the dimensions of the plug that popped out but I'd estimate about 3" diameter? Doing the math that puts it ~7 square inches. A cylinder head pressure of only 2 psi would exert 14 lbs of force against that plug.

[maytag]

Originally Posted by 911monty

Ok so just thinking here and it's later than clock indicates.... I referred to the AOS in the basic term as a pressure regulator which is correct, it is attempting to regulate the crankcase pressure at idle to about neg 4.4" wc. Since the plug is missing on bank 2, the AOS "sees" this as positive pressure in the crankcase and opens in an attempt to draw it down. Since it can't with the hole open then AOS is fully open and ingesting massive quantities of oil to the intake tract. Might be worth getting all plugs back in place and test run.

EDIT: The correct term for the AOS is a diaphragm operated back-pressure regulator.

Okay, I like this working theory (thanks, by the way). The only question it leaves unanswered for me immediately, is probably born from not having a full-scope view of the AOS system in it's entirety: if it's wide-open, as you've postulated, why is it ingesting oil and not air? Do I have a drain-back that's blocked somewhere, keeping the "intake" of the AOS fed with oil?

Originally Posted by 911monty

So to clarify, the left (bank 2?) cam plugs have been blown out and the scavenge pump is possibly not moving oil? Is this also the bank that the camshaft plug may have blown out on? These are not positive displacement pumps. They are rotor. gear pumps. Possible pump damage or blockage downstream at de aerators to sump? Bank 1 (right) could be dry due to AOS directly attached there and most/all oil going to intake?

Originally Posted by 911monty

So to clarify, the left (bank 2?) cam plugs have been blown out and the scavenge pump is possibly not moving oil? Is this also the bank that the camshaft plug may have blown out on? These are not positive displacement pumps. They are rotor. gear pumps. Possible pump damage or blockage downstream at de aerators to sump? Bank 1 (right) could be dry due to AOS directly attached there and most/all oil going to intake?

I don't know which is bank 1 or 2. Someone could clarify for me right now: If I'm facing the same direction as the car, the left side of the motor is the one I'm talking about. Is that Bank 2? Probably, I guess, as it's offset-to-the-rear. ??

Yes, the Left side has the missing large cam plug, the smaller cam plugs that appear to have been blown-out, and the scavenge pump that drained oil when I pulled it out.

[911monty]

Originally Posted by maytag

I don't know which is bank 1 or 2. Someone could clarify for me right now: If I'm facing the same direction as the car, the left side of the motor is the one I'm talking about. Is that Bank 2? Probably, I guess, as it's offset-to-the-rear. ??

Yes, the Left side has the missing large cam plug, the smaller cam plugs that appear to have been blown-out, and the scavenge pump that drained oil when I pulled it out.

This could get long so let's answer this first so I don't get timed out. From rear of car looking forward on a LHD car. Bank 1 cylinders 1,2,3 are on right, passenger side. Bank 2 cylinders 4,5,6 are left, drivers side.

[mikefocke]

I wonder how many times I have posted this link. On a Boxster, 911monty is quite right.

[maytag]

Originally Posted by mikefocke

I wonder how many times I have posted this link. On a Boxster, 911monty is quite right.

Sounds like everyone here agrees?
what'd I miss?

[maytag]

Hey y'all! Great news!
The leakdown numbers are FANTASTIC!
I've got less than 3% loss in ANY cylinder. Honestly, given the consistency and the sealing, I'm still wondering if the P.O. put a new motor in this. I've yet to see any signs of any wear in the motor, and the borescope view doesn't show me anything that looks like mileage accrual on the cylinder walls or piston tops. No carbon build-up, no visible ridge on the cyl. wall. I mean, it's CLEAN!!!


Anyway: this is good news. I now feel confident enough to buy new seals, o-rings, AOS, etc and button her back up.

I'm considering replacing the coil packs, since they're all out, and a couple are cracked. Preferred brand?

I'm ALSO considering a sump / baffle while I'm under there. Preferred manufacturer brand / style?

Anything else I should do? (I already did thermostat & water pump this fall)

[Anker]

Picture is not of a Boxster engine. Intake plenum is on the wrong side, as is the oil fill. Suspect it is a 996 engine.

[P_Carfahrer]

Great news!!!

My car delivered a constant misfire one day this summer and I replaced all my coils with an updated 997 part from Beru. All of the old ones had cracked potting.

I ordered a 2 qt Bilt Racing sump/baffle along with their IMS solution from LN during their 25% - 30% Black Friday Sale based on my reading of multiple forums. Comes with the 997 oil return tubes.

The 997 oil pressure release piston/spring are also something others have done that I will also do when I do the sump/IMS.

All fluids changed?

[maytag]

Originally Posted by P_Carfahrer

Great news!!!

My car delivered a constant misfire one day this summer and I replaced all my coils with an updated 997 part from Beru. All of the old ones had cracked potting.

I ordered a 2 qt Bilt Racing sump/baffle along with their IMS solution from LN during their 25% - 30% Black Friday Sale based on my reading of multiple forums. Comes with the 997 oil return tubes.

The 997 oil pressure release piston/spring are also something others have done that I will also do when I do the sump/IMS.

All fluids changed?

I see your location, but don't recognize the forum name..... Do I know you personally yet?

Yeah, I was looking at that updated BERU part for the coils. I'll probably go that way.

I won't buy the LN sump, so I'll keep looking around and reading as much as I can.

I already did the oil pump piston & spring.

Your "all fluids changed?" question leads me to think that in fact you don't know me yet, haha.
Yes.... all fluids changed regularly, frequently, preemptively, proactively, anal-retentively, and any other way you can think of.

[P_Carfahrer]

Originally Posted by maytag

I see your location, but don't recognize the forum name..... Do I know you personally yet?

We have exchanged emails and PMs but haven’t met yet as I was planning on looking you up at the Oct DE event but I was there Saturday only and missed the now ‘infamous’ Boxster fire at UMP you had on Friday.