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E36 (1991 - 1999)
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  #1  
Old 03-18-2015, 08:58 AM
mojo9430 mojo9430 is offline
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Question Vacuum box question...

Hi,
So, I was replacing vacuum lines on my '94 318is (they were all pretty much crumbling or cracked), and I attempted to remove the one for the vacuum box. It broke off up inside the plastic part of the diaphragm housing. Since I had to go to work, I just capped off the vacuum. My question is, what exactly does this control, and will it affect anything by having it capped off? It seems to run fine without it... I did a search for this and can't find anything covering this part.

Thanks...
[IMG][/IMG]

Last edited by mojo9430; 03-18-2015 at 09:12 AM.
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Old 03-18-2015, 09:22 AM
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hornhospital hornhospital is offline
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It controls the DISA valve. You probably haven't run it above 4800 rpm yet with a wide open throttle. On my 318, there's a distinct jump in power about 4800 when the DISA valve does the change-over from long runner intake to short runner. It won't hurt to run it without the actuator connected, but you're giving up some horsepower at the top end.
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Old 03-18-2015, 09:26 AM
mojo9430 mojo9430 is offline
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Ahhh, ok... I will try to get that off and get that broken piece of tubing out so I can hook it back up... Thanks so much!
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Old 01-07-2020, 10:57 PM
brassman.erdman brassman.erdman is offline
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I read that the DISA fails in the open position, which positions the valve in the high rpm range.

I am aware this is a dead thread, but im trying to find a vacuum box right now, because mine is broken, and I am looking for a new or functional unit and found this post, which based on how the system functions seems wrong.
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Old 01-07-2020, 11:07 PM
brassman.erdman brassman.erdman is offline
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to @hornhospital, i think the jump in power you feel might be your own DISA being inoperative, because im sure BMW designed their system to be smooth and imperceptible, I myself feel a kick in the seat when I rev up to 4600 and up tp 7k, with lots of minor drivability issues under 3500,(mostly due to faulty knock sensors) which led to my current sensor, FI and vacuum refresh, which led to my discovery of a mysterious dead vacuum pod with a linear actuator.

http://bmw3series.johnavis.com/blog/652/m42-engine-e36/

after finding this, the system made sense. Most hot rod American v8 guys have to choose short or long runner; very german to choose not to choose.

but my research (and this very nice technical article) says the valve leaves the runners in short position (high rpm) when the vacuum pod fails.
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Old 01-08-2020, 08:41 AM
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hornhospital hornhospital is offline
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Nope, my DISA valve is working as designed. Ask anyone else that has an M42. There is a very noticeable increase in power at ~4600 RPM. It's not a jolt, more like the rear two barrels on a 4 barrel carburetor opening, like the engine wakes up.
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Quotes to live by:
guessing gets expensive...drivinfaster
nothing is more expensive than a cheap BMW...c4harpe13
buying a ratty example (of a BMW) is a parasitic relationship.(and you ain't the mosquito) 7pilot
Ken Kanne, Silverhill, AL, Bimmerfest Site Moderator
BMW-CCA #441426

1993 325is M3 clone"Ashlyn"; 1993 325is "Elvira"; 1985 635CSi "Katja"; 1984 633CSi "Sylvia"; 1987 325is "Odette";1995 318is"Bebe "; 1985 325e "Hazel Ann"

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