Complete Vacuum Replacement
The vacuum system in a Porsche 944 Turbo (951) is very complex. In the 1980s, there wasn't much computer power to regulate turbo charged cars, so most of the workings were accomplished by mechanical vacuum systems. There are over 30 feet of vacuum hoses in a 951. Also, there is MUCH more to the vacuum system then the small diameter lines you're used to in other cars. There are also numerous large diameter hoses.
An improperly working vacuum system can lead to all sorts of problems. If you have recently bought a 944 Turbo and do not have maintenance records, I recommend replacing all of the vacuum lines.
This guide is specifically for a 1986 Porsche 944 Turbo in which I replaced the venturi tube with hoses. Other models may be similar, but some changes were made over the lifetime of the 944 Turbo.
Take waste gate hose (951.123.331.02) and feed the straight end down the firewall toward the waste gate. Place the sharply bent end over the timing valve. Do not tighten the hose yet. You want it to be loose so it will slightly rotate when you put the waste gate side in place.
Slip the straight side of the hose over the nipple on the waste gate. Tighten the hose clamp on the waste gate first, then tighten the clamp on the timing valve.
Cut 10cm of 5/16" fuel hose for each of these two hoses on the vacuum manifold. 10cm will be a little long, but you want to trim them in place to make sure you do not side load the nipples on the timing valve too much. Insert the elbow shaped hose (931 110 183 01) onto the Air Oil Separator. Install the vacuum manifold by pushing the large pipe end into the elbow hose. Then attach the vacuum manifold in place by screwing in the support bolt towards the front of the manifold.
Trim the two hoses for the other two timing valve nipples until they are practically straight, but still have a bit of slack in them. If the hoses are too long, the excess bend will put side load on the timing valve which could break the weak plastic nipples.
Run a length of 5/16" fuel hose from this port on the fuel vapor purge valve down near the J-Pipe. We'll come back to this later.
Run it to the front of the coolant reservoir. We'll come back to it later. The hose that you are replacing has a elbow fitting on the end of it. You will need to recycle this part. Stick the elbow in the hose so you don't lose it. This line will go inside the J-Pipe later.
Find the line that went from the brake booster to the venturi. We'll be replacing this line with one of the lines from the venturi delete kit. However, you'll need to save the white plastic tee and the brake check valve. You'll re-use those later.
Line up the old hose with the newsvendor delete hose (951.110.223.01) as close as possible to find the correct cutting locations.
Cut the line and install the white plastic tee and put the hose together. Insert the correct end into the brake booster vacuum port. Leave the other end loose. It will be installed into the intake manifold.
Next you'll need to attach some of the small silicone vacuum lines to their proper place. At the firewall near the battery, there are two small nipples. Attach the small silicone vacuum line from the top port and run the line to the vacuum reservoir, this will get a tee fitting later. At the lower port, run vacuum line from the nipple to the heather control valve, which is located in line at the heater/coolant lines running near the block.
Here is a close up of the heater control valve at its' location hanging behind the block.
You will now need to install a tee fitting on the other small vacuum line you just installed. Put a small amount of vacuum tubing before the straight portion of the tee.
Run a smell length of vacuum tubing from the small vacuum tee to the large white vacuum tee on the brake booster to intake hose. The side of the picture shows as open will connect to the brake booster check valve (shown in next picture) and the tee on the line that you just ran to the vacuum reservoir behind the firewall. The side that the picture showed connected will run to the fuel vapor purge valve (shown two pictures down) which is located on the fender next to the brake booster.
Here you can see how the brake booster to intake line splits off. The right side of the first tee goes to the fuel vapor purge valve. The left side of the first tee runs to the brake booster check valve (make sure it is properly aligned), then runs to another tee which runs to the vacuum reservoir and the vacuum supply line at the firewall.
Here is where the line from the brake booster check valve finally ends at the fuel vapor purge valve (bottom connection in picture). Run a new line from the top port of the fuel vapor purge valve to the thermo valve (shown in next picture).
This is the thermo valve. It is located near the cycling valve. There are two ports on the thermo valve. The port that sticks straight up is the one that goes to the fuel vapor purge valve (the line you just started running). There is another port that is slightly bent at an angle. Install a new vacuum line here, run a bit of vacuum line out to where the throttle body will be and leave it a bit long. You'll have to connect this later.
Next, install hose 951.110.221.00 to the idle air stabilizer/valve. Leave the other side disconnected, as this hose attach to the intake manifold.
Since the vacuum manifold is only available as a complete unit, we have to figure out a way to replace all the rubber lines separately. All the lines from the vacuum manifold can be replaced with 5/16" fuel line except for one. This is a molded hose. The hose is crimped on and will have to be removed from the vacuum manifold by cutting off the crimp. I used an angle grinder with a cut off wheel to cut through the crimp and hose. Be extremely careful not to cut too deep, or you can damage the vacuum reservoir. The hose removed from the vacuum manifold is the top hose.
A bypass hose from a 1979 Honda Accord is a close replacement. The Gates part number is #21221. It is the bottom hose pictured. As you can see, it is a little long. You will have to cut it to length, so match it up with the old one.
You'll need to use this Motor mite 3/4" x 5/8" heater hose adapter to hook this hose into the J pipe. It is part #4780 and should be in the HELP! section of the local auto parts store. If you don't see it, you might have to order it, or they could have it in the back. Just give them the number.
Here you can see everything assembled. Since the Honda bypass hose is a little bit smaller in diameter than the factory Porsche hose, you'll really have to push to get it on the manifold. Honestly, I had to result to lubricating the manifold with Stogie to get the hose around it.
Use some 5/16" fuel line to run this line. It goes from the J-Pipe to the metal tube on the vacuum manifold.
Install the intake manifold on the engine. Pay special attention to the intake gaskets! The one closest to you does not go on like the other three.
Attach hose 951.110.217.01 from the idle control valve to the front intake manifold port. Attach the long hose from the brake booster (the one you cut and put the old white tee in) to the rear vacuum port on the intake manifold.
Attach the fuel rail to the intake manifold. Next, take small vacuum tubing and make a circle starting at the fuel pressure regulator, under the intake manifold, and ending at the fuel damper. Cut the line, and then install a tee as shown in the picture. Run a small length of hose and then run off the tee to the vacuum port on the intake manifold.
The clear plastic line that shares the same port on the vacuum manifold runs to the KLR, which is located in the passenger floorboard. You can replace that if it is bad.
There was a line that you started earlier that I told you to leave long. This line goes to a small nipple on the bottom of the throttle body. You can go ahead and attach this line to the throttle body now.
Remember that line that made the circle from the fuel pressure regulator to the fuel pressure damper? You'll need to cut that line again, and install another tee. This new branch will run to the bypass valve.
This shows the bypass valve in place with the line you just ran installed on the top port. Also, connect hose 951.110.511.00 to the inter cooler charge pipe.
Use 5/16" fuel line to run this line from the vacuum manifold to the charge pipe. This is also the line that you would replace with a boost enhancer, if you decide to go that route.
