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Old 09-16-2009, 02:35 PM   #1 (permalink)
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Vehicle: 1999 SLK 230K (R170). 96k Miles
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Oily MAF and the supercharger air bypass valve / butterfly

Hey Folks,

After losing acceleration power recently (e.g. making any overtaking difficult) I ran a scan to find:
0170
P0243

(using CarSoft 7.4)

I inspected my MAF to find it was covered (once again!) in a light coating of oil (brighter and more yellow looking than the engine oil). One possible cause of this (from searching the forum here) is the supercharger air bypass valve / butterfly not closing. So to test if this was faulty I followed the advice from a post of Bazzles:

"The only test I know is to rev engine with pipe removed from top and see if it closes as clutch engages. "

Here in the picture I think I've identified the part... A friend revved the engine in neutral up to about 3500rpm and the butterfly never closed, but at (about) 2000rpm the pipe started blowing hot air (I presume this means the supercharger clutch engaged).

Do people here feel I have identified the correct part?
And perhaps it's faulty based on the test I tried?
Am I going in the right direction?

Many thanks!!

Hugh

p.s. After cleaning the MAF, the car has regained it's acceleration power and feels good. But I presume it's only a matter of time before I get an oily MAF again!

p.p.s. Mechanic that I brought it to recently was of the opinion that oily MAFs are a symptom of all MB kompressor engines!
Attached Thumbnails
Oily MAF and the supercharger air bypass valve / butterfly-dsc00007.jpg  
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Old 09-16-2009, 08:38 PM   #2 (permalink)
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yep common problem oily MAF is a result of the oil separator (search for it here)... one hose to it prob has degraded and its stopped functioning and pushing oil into intake system...

also ive noticed the hose going to your airbox is the wrong way around! (not that it matters too much but still)... (see pic).

bypass only equalizes system when not in boost, and flap closes shut to build boost (i.e. engine under load & accelerating hard).

it wont shut in P or N (no engine load - revving it wont do it) has to be in gear and moving. air blowing indicates clutch is engaged and supercharger is blowing air OK...
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Oily MAF and the supercharger air bypass valve / butterfly-01_passanger.jpg  
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Old 09-16-2009, 08:48 PM   #3 (permalink)
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check where that green circle is that little rubber hose which goes to supercharger... that over time degrades... (it sits right next to engine/exhaust)... i zip tied mine AWAY from the engine against another hose so its not near the heat or touching the cam cover..

if this is broken it will create a minor boost leak as boost is being lost from the supercharger... attached is a pic of mine (when i found it broken)
Attached Thumbnails
Oily MAF and the supercharger air bypass valve / butterfly-engine-bay-rh-_800.jpg   Oily MAF and the supercharger air bypass valve / butterfly-11-09-07_1958.jpg  
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Old 09-17-2009, 06:09 AM   #4 (permalink)
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Hey Subby,

Thanks for the pictures! (makes things 100x easier!). So for the moment I'll disregard the air bypass valve as the source of the problem.

Very interesting that you spotted the tube to my airbox is a different way round to yours, I wonder what affect that will have, if any! Not sure if this has ever been moved but I can see the engine bay of another Irish SLK and it appears the same way round as mine:
http://www.benzworld.org/forums/r170...tallation.html

Maybe yours is just a down unda' thing? ;- )

Good advice on the oil separator - I did clean it about 6 months ago and replaced all of the larger tubes since they were beginning to crack. But the tube to the supercharger I *haven't* replaced (couldn't find the part number at the time) - I'll take off the oil separator tonight and check all four tubes for blockages - especially the one to the supercharger.

One thing that still puzzles me - the oil in the MAF appears to be brighter or more yellow in color than the engine oil - which is presumably what is going around the oil separator. So hence I'm not 100% sure that the oil separator is the source of my oily MAF?

Hugh
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Old 09-17-2009, 02:06 PM   #5 (permalink)
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Hiya,

I've checked the line from the supercharger to the oil separator - it seems intact and not blocked - a little bit of dirt came out but nothing major. And the hose that goes from the oil separator to the air box seems (reasonably) dry - so looks like the oil separator is actually doing it's job!

I understand now what the line from the from the supercharger to the oil separator does - adds compressed air to increase the contrifugal forces to separate the oil out... and yes this would explain why if this line was broken or blocked it would hinder it's performance. I had seen screenshots explaining it, but I've created a PDF which might be a little easier to read (see attached).

So where to next? :-)
a) Could there be oil being blown up from the supercharger (through the hose with a wire wrapped around it)?
b) Remove the intercooler and clean it out? (I'm searching for instructions on how to remove this at the moment)
Attached Files
File Type: pdf Spiral oil separator, function.pdf (90.0 KB, 542 views)
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Old 09-17-2009, 02:37 PM   #6 (permalink)
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Your hose is in the wrong position. Take it off and flip it! Cmount was trying out an oil catch can and put his on backward. You crazy Irishmen.
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Old 09-17-2009, 03:05 PM   #7 (permalink)
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Lol. Trust me to find the only other person on the forum who's flipped their air hose! Will try that next so :-) cheers!

(oh but I still think I should consider cleaning out the intercooler somehow... start afresh!)
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Old 09-19-2009, 10:10 AM   #8 (permalink)
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Right - I've taken the hose that was the wrong way around and corrected it. Looks better now, thanks guys! :-)

When I took off the cover to the airbox, I could see some oil coming in. See 1st attached pic.

So I was wondering where I was coming from... I checked the three hoses coming into the air box: The hose from the oil separator is bone dry, the hose I flipped was a little dirty but dry, but the hose from the supercharger seemed oily. Taking it off and looking into the supercharger I could see oil around the rim and inside it (see 2nd pic).

Could this be the source of my oily MAF? Anyone with a similar experience?

Hugh
Attached Thumbnails
Oily MAF and the supercharger air bypass valve / butterfly-dsc00017.jpg   Oily MAF and the supercharger air bypass valve / butterfly-dsc00024.jpg  
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Old 09-19-2009, 08:28 PM   #9 (permalink)
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humm had a look at my stock air box (dont use it anymore) and it has traces of oil vapor on it (which its supose to)... I think yours has way too much

3 hoses explained

1st one - this one connects to the airbox. in theory it should be "sucking oil vapor" from the oil seperator.

2nd one - the thin 3mm rubber hose going to it. this pushes air (boost) from superchager in the oil sperator spiral to help seperate oil/oil vapor

3rd one - this one connects down to the dip stick to let oil drip down back into the engine


in my case when i got my car a while back hoses 2 (complelty degraded) and hose 3 split apart due to its location near the exhaust area. i didnt use benz specific parts (again couldnt find number). took it to an auto store and got some rubber hose cut up. fitted fine

i think in your case hose 2 has a split somewhere and its not doing its job seperating oil/oil vapour and its being sucked into intake... have a closer look. can take it to an auto parts store im pretty sure its just plain 3mm vacuum hose. then zip tie it away from the exhaust area as you can to anther hose nearby.

would be a good idea to clean out the intercooler (ive done it). (search around). not a hard job at all. only tricky part is taking off the front bumper (once you have done it once its easy...)

i know oil vapor has to be vented BACK into the intake but what i DONT get is why did benz to chose to do this thru the supercharger/intercooler/MAF... wouldnt it be wiser to vent it into the intake manifold bypassing the lot incase of say failure??!
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Old 09-20-2009, 06:35 AM   #10 (permalink)
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Thanks for taking a look Subby.

What I find confusing is that I thought if the 3mm hose from the supercharger to the oil separator is leaking or blocked then the oil separator wouldn't be able to do it's job properly and as a result there would be oil in the hose that goes from the oil separator to the airbox? (but it's bone dry)

(or maybe I'm not understanding the hoses correctly).

After taking it (the 3mm hose) off, blowing through it and spraying thorugh it, it *seems* okay. Couldn't hurt to replace it though!

Anyway - I agree that removing and cleaning the intercooler is the next step. I had searched around before on intercooler but really I should have been searching on removing the front bumper - here's the link I found:
http://www.benzworld.org/forums/r170...-supports.html

Also I put together a PDF from the WIS instructions on how to remove the front bumper - see attached.
Attached Files
File Type: pdf Removing and installing front bumper.pdf (224.8 KB, 396 views)
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