rawky

(1991 S4)

Hi Everyone,

...would it be possible to re-connect it without removing the intake?

I only ask because I think it might have come adrift. I changed the vacuum spider recently and I felt the line going under the intake resisting my (gentle) pulling at it to release it from the spider. Then the line seemed to break free and come 4-5in further out from underneath before it resisted again.

Now when I put my vacuum pump onto the front fuel damper vacuum line I can hear a faint hiss from the back of the engine as if something is now disconnected.

I will of course go in there soon and test each line for vacuum to find the leak, but just wanted to know that if it turns to be the under-intake line I'm not in for days of work?

Cheers

9x8

It is possible, but is surely very tricky.

Jascd

yes it is possible if its the line to the throttlebody but very unlikely if its the one to the flappy. You will need to remove the maf and that will give you better access to the TB. I have done this when I did my intake and found that I had routed a line wrong and was able to disconnect and re-route it with the intake in place. Have a look though the legs of the intake (wiht the fuel rail covers off) and you might be able to see what is needed if its the TB line.

An inspection snake might be handy as well as some long pliers.

cheers


Jason
89 S4

Tails

I have reinstalled the vacuum line to the right angle pipe located on intake suction between the MAT and intake butterfly valve by only removing the air filter box, however it is extremely difficult as I was using a small 12 volt light and a mirror to feed the tube back onto the right angle pipe.

The pipe between the vacuum spider and the right angle pipe has a small band on the end of the pipe at the to ensure it is secured to the right angled suction pipe to keep it secured.

An easier way is to remove the air filter box, the MAF by undoing the jublee clip located on the rubber connector adjacent to the inlet butterfly valve housing. Access is gained to the inner jublee clip screw from the driver's side of the manifold on RH drive cars under neat the intake manifold between the last two inlet pipes. Again as small 12 volt light, suitably shielded so that the light shines on the jublee clip and if the jublee clip screw head is located on the driver's side of the inlet manifold it can be undone far enought to slide the rubber connector off with the MAF.

If you can remove the MAF as described you will also have access to the aft knock sensor, the aft section of the block valley, the engine speed sensor, the aft fuel pipes the fuel pressure regulators and lots of other items that can be given some maintenance.

WYAIT it would also be a good time to clean the earth connections located in this area.

Tails 1990 928S4 Auto

rawky

How do I distinguish between whether it is the line to the throttle body, or to the flappy mechanism?

It goes from the spider directly underneath the intake in a straight line if that helps?

Concerning the flappy mechanism vacuum line, am I wrong that I thought that was connected to the HVAC vacuum system?

Cheers

Bill Ball

There are two vacuum ports on the TOP of the throttle housing and one on the bottom. See pics below.

The vacuum source line to the 5-way ("spider") at the back of the motor SHOULD go to the TOP of the throttle housing, pretty easily visible and accessible with the MAF out. That port, shown on the left in the first photo, faces the rear and has a line that goes to it via a rubber connector. My stock line as a couple of hard sections and straight rubber connections, any one of which may come apart.

The other port on the top of the throttle faces forward and has a 90 degree elbow on it and a white line that snakes over to the tank breather valve.

The only line on the BOTTOM of the throttle housing SHOULD be the line which goes under the fuel rail on the front passenger side to the air pump diverter valve. The port is shown in the second photo with the throttle flipped over. It's connected to a black hardline via a 90 degree elbow.

The line to the flappy actuator is separate and is not connected to the 5-way at the back. So, that's not it.

rawky

Wow, thankyou Bill. I'll get down to finding the disconnected line, and work out which one it is. I am assuming any of these three lines could be the source of my leak?

Cheers

P.S. Does the fact that the vacuum line going under the intake from the spider is the vacuum SOURCE mean that it won't pull a vacuum when tested? or does it create a seal when the engine isn't running?

rawky

UPDATE: The line had become disconnected, and now I've re-connected it and all's well. The photo's were priceless, helped alot!

Only bad point was that after re-installing the fuel rail on the driver's side (RHD) the rear-most injector won't seal against the rail properly! One for the morning I guess, any pointers on that?

blown 87

Bill, I think that on some of the early S4's there are two vacuum ports on the top and the bottom.

For what that is worth.

x98boardwell

Reviving this one. Bill, I am in the process of putting the intake back together. On your photo above (the first one) where there are two ports facing in different direction my car had the white line heading the other direction (so no 90 degree angle) and went straight towards the back of the photo. I have a 94' GTS. Do you know why this was traveling towards the front of the motor rather than the rear?

Bryan

Bill Ball

I've seen it both ways. In fact, the diagrams in the WSM are confusing and not specific regarding the exact routing. Mine were routed differently when I got the car and i knew the intake had not been touched since it left the factory.