Tuner1

1989 944 turbo. Today I found this black vacuum/boost hose tucked down near the battery. It originates at a 3-way Y fitting just ahead of the firewall and it sucks vacuum as soon as the engine is started. I looked around near the firewall/battery/HVAC fan area but can't see where it attaches to

Darwantae951

Hooks up to the bottom of the black vacuum reservoir on the other side of the positive battery cable in your picture. There should be a nipple protruding from the bottom.

Pardon the crappy cell phone pic:

Tuner1

Thanks I didn't see the nipple so maybe mine is broken off.

What function does the "vacuum reservoir" serve?

Scott H

It holds vacuum for the A/C and ventilation systems.

TurboTommy

Mine is also broken off.
What could be a likely repair? Can we drill and tap into the face of this canister? Then tap in and seal a vacuum fitting?
Also there's another vacuum coming out of the firewall a little closer to the bell housing. What does this one do?
What exactly happens when any of these gets no vacuum source?

Scott H

Starting from the check valve in the vacuum system:

The check valve makes it so no boost can get past and it will only pull vacuum. The canister will hold this vacuum while the car is in boost/not making vacuum. There are then two vacuum ports on the firewall in the engine bay. The top port pulls vacuum for the 3 electronically controlled valves that hold the fresh air flaps shut, and the heater flaps. If you lose vacuum these flaps open and allow hot air to enter the cabin. The lower port on the firewall comes from inside the car and is connected to one of the electronic valves, this one controls the heater bypass.

If you can find the A/C vacuum diagram it will all make more sense. I believe Clarks has the diagram in one of this A/C tutorials.

TurboTommy

Are you saying there two vacuum ports in the engine bay besides the the vacuum nipple on that canister?
I only see one line running into the firewall; I'll have to look again.

And what do we do without that nipple on the canister, and what does that canister do, exactly?

Scott H

Yes, there are two more A/C related metal vacuum nipples behind the engine, above the coolant lines running into the cabin on the firewall. Kind of hard to see because the engine harness will be in the way.

Without that nipple, well, just buy another vacuum canister, they're $10-15 on eBay. The vacuum canister just holds a vacuum for all of the HVAC related components (vents, valves, etc.)

This link: http://www.clarks-garage.com/shop-manual/hvac-01.htm makes it a little more understandable.

Darwantae951

Here is a photo of the above mentions HVAC vacuum ports behind the engine:

NM'87 951

I know this old thread, and my apologies. I have a couple of ?'s regarding this system right here.

1. Are those supposed to be hard plastic lines, or will the LR silicone vacuum line kit work in place?

2. Is there supposed to be vacuum 'suck' from the top nipple, that runs to the vacuum canister (there appears to be NO vacuum on either of those lines coming out of the firewall)?

3. If the car runs the same (and that is to say stable idle, with severe dip in idle after de-acceleration) with these lines connected or disconnected, do I have a bad HVAC controller or something?

Car worked well after installing the vacuum lines. Had a drop in idle (down to 200rpm) after de-acceleration... and some severe 'pulling up' after accelerating past 2000rpm in gear (car goes, let off gas and it feels like I stomped on the brakes). I think I can hear a leak, so I'm going to take her apart and put clamps and ties on EVERYTHING. The car ran pretty nicely for a few days, then started developing these problems which seem to have gotten worse. Now I can't get boost (just starts cutting out and hesitating, never developing boost), so wondering whats wrong.

I'm starting to get that this car is going to take more from me than just my money

NM'87 951

Nevermind. I've come up with some possible causes to my problems, and a checklist of things to do. I'll post when I get some results to talk about.