Author Topic: M42 Vacuum Diagram (Read 84112 times)

RIPDOTCOM · « **on:** November 24, 2007, 07:29:56 AM »

Picked up a 91 318 2 days ago. Had a bad fuel pump but the previous owner pulled apart the IAC system and any hoses that go to the intake boot as well as the pcv hose. I can tell you where everything goes on an M20 with my eyes closed but this is my first M42. Does anyone have a basic diagram showing how the system is plummed up? If you have a pic send it to ripdotcom@comcast.net or post a link here. Also , if there is anything not required to be hooked up please note it.

Wise Old Dog · « **Reply #1 on:** November 24, 2007, 07:53:25 AM »

Do a search. It has been covered many times. I think D Clay posted a good drawing recently.

strad · « **Reply #2 on:** November 24, 2007, 10:56:33 PM »

Grossly simplistic, but. . . valve cover breather connects to throttle body, and icv connects to intake air boot -- and there's a whole mess of other things in between!

RED IS 91 · « **Reply #3 on:** November 25, 2007, 07:25:54 AM »

From the stolen file...................Hope it helps
good luck

tjts1 · « **Reply #4 on:** November 27, 2007, 06:28:30 PM »

Quote from: RED IS 91;38307

I would love to have 5 minutes of one on one time with an aluminum bat and the person that designed that crap.

RED IS 91 · « **Reply #5 on:** November 27, 2007, 07:29:25 PM »

Quote from: tjts1;38453

I would love to have 5 minutes of one on one time with an aluminum bat and the person that designed that crap.

Some people say it's simplistic .:eek:
" I dunno about that"

Once again , gl

D. Clay · « **Reply #6 on:** November 27, 2007, 09:23:42 PM »

It's been so long that I forgot where I found that image.

strad · « **Reply #7 on:** November 27, 2007, 11:58:32 PM »

Quote from: RED IS 91;38460

Some people say it's simplistic .:eek:
" I dunno about that"

Once again , gl

I didn't mean the system was simple lol. Just my explanation of it.

It is actually really simple -- BMW just used about 10 too many parts to put it together lol.

tjts1 · « **Reply #8 on:** November 28, 2007, 10:04:32 AM »

Why does the crankcase ventilation or the idle air need to be preheated with coolant? Who the hell thought that was a good idea? I'm surprised they didn't preheat the preheat. On a volvo for example that whole preheat mess is contained in 1 component. In the intake to the airbox there is a trap door that rotates between cold air from the grill (on th left) and hot air from near the exhaust manifold (right). It tries to maintain a minimum 70f intake temp.

Mind you its not perfect either. After 10 years or so the thermostat always fails on the hot air side so most of the old non turbo volvos you see driving around are actually sucking down 180f intake air through a straw. And people wonder why volvos are slow. But at least it can be fixed with some pliers and ball of aluminum foil.

RIPDOTCOM · « **Reply #9 on:** December 04, 2007, 07:49:33 AM »

I did a search after I posted (a little overzealous) anyway, capped the 2 ports and re routed the pcv and IAC. Runs rough but its getting there.

mkodama · « **Reply #10 on:** May 11, 2008, 03:56:28 AM »

Well, I like to improve/simplify things so here are the thoughts going through my head:

Things that need to connect to the vacuum port behind the throttle:
1. Fuel pressure regulator, to compensate for intake vacuum
2. Idle air control valve, for a faster idle during warm-up
3. Crankcase vent, to create a vacuum in crankcase/burn vapors

So why not do this? Any thoughts or opinions?

as opposed to this mess

ClodKing · « **Reply #11 on:** May 13, 2008, 06:16:03 PM »

Yeah my engine is in pieces right now. An answer to this would be great before I put it all back together again...

mkodama · « **Reply #12 on:** May 14, 2008, 02:34:51 AM »

Quote from: ClodKing;49253

Yeah my engine is in pieces right now. An answer to this would be great before I put it all back together again...

I wish I had my 318is right now, but unfortunately I won't have easy access to it for the next few months so I can't experiment and give you a straight answer right now.

The concept of everything is pretty simple as shown in my diagram that needed only 3 lines. BMW just made things more complex by adding additional tubing to preheat various things with the coolant and so on. In general, the factory setup and routing of vacuum lines is the safest route to follow at this time.

Hopefully in the future I could test the other options and have a clear response.

haledj · « **Reply #13 on:** May 14, 2008, 03:23:11 AM »

The idle control valve needs to connect before the throttle, the other two need vacuum.

That's what the barb on the intake tube is for.

mkodama · « **Reply #14 on:** May 15, 2008, 03:16:19 AM »

Quote from: haledj;49288

The idle control valve needs to connect before the throttle, the other two need vacuum.

That's what the barb on the intake tube is for.

Ahh, I was initially kinda confused by that statement but understand it now. The confusion/problem is just from the not so good drawings, so I've decided to redo them. I appreciate the input, thanks.

RED: Intake Boot to Idle Air Control Input
GREEN: Idle Air Control Output to Throttle Body Vacuum Port
BLUE: Engine Vent to Throttle Body Vacuum Port
YELLOW: Fuel Pressure Regulator to Throttle Body Vacuum Port

Any problems or confusions with this setup?

And, which ports specifically on the throttle body have vacuum and which don't(if any)?