I submitted a reply to another thread regarding vacuum lines… But I’m not sure it was the right thing to do. While checking for leaks in the vacuum lines on my 1987 S4, I found this line that runs along the back of the bulkhead which is a clear pipe below the airbox. It looks like it was once plugged into something and the other and goes to the in a guard just underneath the coolant bottle. This is on a right hand drive vehicle. It would appear that I don’t have a vacuum leak but I am intrigued as to what this is… Any help please, including where I should stick it!… No smart comments please :-)


any help will be appreciated

 

My first thought, considering the location would be to check the heater flow control valve. It is directly below and rearward of the FPR - visible in your picture. Also, take a look at the vacuum lines that come off the brake booster 4 way connector on the right (being RHD).

 

I will try to see down there but it’s very tight and it’s taken me ages to get my hands in to check vacuum lines at the 4 way junction full stop. I ended up checking the line at the front that feeds it and it held vacuum great, so no more messing with the 4 way. The heater flow would make sense as it’s not going where I need it in the car when I move the slider. Off works as does defrost but it still comes out all the other vents on any setting. All other systems work well on my car so whatever this pipe is must be something very specific that doesnt interfere with other things. Would it be correct that this line would go across the firewall in to the guard underneath the coolant reservoir ??? I guess it could have just been tucked up there out of the way ??? I just put it all back together so I’ll have to attack it tomorrow again. Will it be easy to see where it should attach ??? Cheers with beers. Al

ive just added to this with some photos which make more sense. I disconnected the 4 way and brought it in front of everything before re connecting so you can see what’s connected. Everything seems to be in place and it’s holding a vacuum from the front of the engine which is where the black feed comes from. The mysterious pipe is shown at the top and was clearly connected to something, it’s been ages since all this came off and everything has been working ok, the air con direction can be a bit vague and the air in is t really working much. Also, it just just blows slightly warm air all the time unless you crank it on hot then it comes through hot. It would appear that inside the fender ( 2nd photo ) is the vacuum reservoir which is where the other end goes... but if it’s completely open surely just about everything will not work ??? . I just need to know where to reconnect to and is it worth checking vacuum in this line before i put it all back together. Should the engine be running when I check the vacuum and will it take long to charge the resevoir ?? Sorry so many questions but it seems like an easy fix for something I didnt know what was broken !!!

This is the end that goes into the fender, I’m assuming to the vacuum reservoir ???

This is the open end under the air box. As you can see, all other connections are secure in the 4 way... where the heck does it go ???... and what does it control ??? If it’s the heater control valve I can’t see where it goes.

 

I’m still waiting to a flash of inspiration from somebody else but, in the meantime, I have been searching every forum on this. The problem I can see with every forum I see is that they are on a LHD car so its all on the opposite sides as mine being a Right Hand Drive one. I guess this doesn’t really matter too much but some of the configuration changes. The more I read , the more it would appear that my ‘spare, random and OPEN’ vacuum line is the one that leads to the vacuum reservoir. If this is the case then the reservoir is not doing anything at all. What is its function and how come my car runs just fine with an open end to that clear line ???. I seem to be missing a ‘Y’ shape connector that connects the clear one with a black one....but which black one ??, I have two black and neither go to the fender. I am concerned that this has been fiddled with over the years and the mechanic has got confused and just gone to his memory for a ‘best guess’ I resurrected this beast after 12 years of sitting idle so I cant remember who worked on it last. I’m sure they wont remember if I did find them. The upshot is that it would appear to be in a bit of a mess, its conveniently still working, I’m not sure where it all goes and I think I’m missing the Y connector. What is likely to start working if I split it with one of the black ones ??? My thought are, the Y piece has gone missing, the reservoir is charged from the 4 way splitter and only acts as a reservoir to keep vacuum for a bit when the engine is off. So, based on this, if the reservoir is isolated and not charged from another source then it doesn’t matter if its missed out of the circuit...is that correct ??? I know I seem to be answering my own questions but if I vacuum test the ‘open’ reservoir line and it holds, ill just get a new Y piece and add into the circuit again. Please help as I’m such a noob with this stuff and this community has got me out of a pickle more than once. I’m just adding more info and photos as I get them but its sat in bits in the garage waiting for confirmation I’m on the right track....Cheers. AL

 

The disconnected line (vacuum reservoir) can be connected to either black hose (with a T or Y fitting) as they are all connected together and at the same "pressure". You could buy a hard fitting with some soft tubing at your car parts store and hook it back up. Note the heater valve line (white) at the bottom in your picture is connected. I suggest buying a 4 way hard fitting while you are at it, so when the rubber one breaks, you can at least put it all back together.

 

I think the plumbing is basically the same as my S2, in which case it is the reservoir which is behind the splash guard behind the passenger front wheel. Without it connected some things will only operate properly when the engine is idling and pulling a decent vacuum. If you have a hand pump, make sure it holds a vacuum before re-attaching, it may have been disconnected for a reason

 

Does that go to the vacuum accumulator. ? The device that collects and stores vacuum. Its in the driver side fender on a left hand drive car...

looks to be thicker than a standard vac line also.


pull of the splash guard of the wheel-well where it leads to...you will have your answer.

 

Do you have cruise? In 87 the cruise control was vacuum operated and that sits next to the vacuum reservoir.

Also, manual or auto?

I have a RHD 87 S4 so can grab some pictures later in the week if you don’t get an answer in the next few days.

Duncan

 

Hi everyone...thank you so much for your assistance so far

Just a reminder that mybaby is a RHD 1987 S4 with no cruise control. However, there has been a huge development today. I managed to find a T piece, as suggested, and connected the loose line up in circuit with the black feed line. Got it all back together and whammo !!!!, the brake sensor warning lights have illuminated and wont go off and the front fog lights have stopped working. The only thing I’ve touched is the vacuum line, Now, I would say I’m unlucky but this cant be coincidence as I’ve had the car for ages and it all, I and I mean everything, has worked fine since being resurrected a year ago now this hmmmmmm...so Ill have to disconnect it tomorrow and find out what will happen if I put it back to an open line again. One thing to note is that my mechanic at work said the brake pad warning sensors at the front had been ‘bridged’ so, I’m thinking that maybe years ago when it got serviced the brake pad warning light came on and whoever serviced it then couldn’t get it to go off, they might have figured out that disconnecting the reservoir line somehow stopped the problem ... but it doesn’t explain the bridged sensors. Who knows. This is sooooo weird. So, my choices are to replace the brake pad wear sensors and leave the vacuum line on...OR, return it to how it was, hope it all works again and bury my head in the sand. This is really confusing and doesn’t seem to follow any logic. Thoughts chaps ???

AL

 

Thnak you Duncan, any photos that are of the same model will help a lot. Thank you !!!

 

I have no skin in this game; but very interested to see how this all plays out. There are some absolute 928 superstars on this forum.
call me subscribed!

 

Long shot...but it's not part of the headlight adjustment system talked bout in a recent thread is it...

https://rennlist.com/forums/928-foru...ight-****.html

 

Well, I was that annoyed last night at two things not working that I stayed up till 2am trying to fix what went wrong. Anyway, the lights got fixed, turns out that it was the dash board switch through lack of use. After lots of checking and less of it it came back to life and was all good after that. I need to clean the contact. So, based on that, it’s time I pulled the instrument cluster out and cleaned some contacts in general. I have the occasional ‘ dancing dials! Which is obviously due to storage etc... so that’s done... well it will be ! Next into the random brake sensor fault that turned up. I refuse to believe it’s linked to the vacuum reservoir being connected back up after all these years ! When I can get it up on the ramps at work I’ll check the pads and sensors and see what happens. I guess this thread is just turning out to be a story which needs little input from everyone else :-)

 

Hi Tony,

I can’t get into that thread you sent, I’m open to all suggestions at moment.

I started looking though the threads on instrument cluster removal and decided to hang on till we’re out of lockdown just in case I need some bits.

I must admit I’m thinking, now I’ve got the lights going again’, that it’s just some complete coincidence and the brake sensors have decided to break at this moment to mess with my head. The only way to solve that is new pads and sensors all round....hopefully this one is simple but it still doesn’t answer the original question as to what the reservoir does as it’s running no better or worse than before when it was completely open and all other functions and performance appear exactly the same. It just seems like a surplus bit of kit ?! Why would Porsche do that ??? There must be a reason.

 

If you didn't have a vacuum reservoir connected to the engine with a check valve, there would be no vacuum available to operate vacuum operated devices at times the engine wasn't producing vacuum.