Porsche Enthusiasts Club Forum

I was wondering if anyone that has an 944S (or S2 if they are the same layout) can help and have a look at their vacuum pipes on the bulkhead?

I have just completed a full engine rebuild and whilst marking everything up I have two vacuum pipes that seem stray. I am also having some running problems so would like to get the vacuum pipes correct before continuing the hunt for running issues.

This green pipe going through the bulkhead to the heater is stray, it did have a rubber end on it but that is now missing, where should this connect? As it had a rubber end on it I've eliminated it from going into the T piece.





This other T piece (purple line, below pic) on the bulkhead only has two connections, one to the valve on the coolant pipe that runs over the exhaust manifold and one going to the brake servo check valve, what should be in the third hole?



This is how I am currently set up with hoses, showing the two open pipes, the short green one going into the bulkhead and the right T piece in blue. Yellow line is between the fuel regulators and inlet manifold.



Onto those running issues, when I first drove the car on Sunday it didn't seem to want to idle when coming to a halt, also the same when I dipped the clutch whilst driving along, it would just stall although I could bump start it when driving with the momentum of the car. It drives great on the throttle so I'm not thinking fuel delivery.
When it stalled it did eventually start but this was after about 20 minutes being sat, I drove it home and it stalled on the drive and wouldn't start when I tried, just turns over and over. I left it for an hour and went back out where it started first time.

The next morning it struggled to start and had to give it some throttle but when driving this time it seemed to idle better when coming to a halt. I don't think this is a vacuum issue but would also like to hunt down what it is as I've got 500 running in miles to do before I can give it the beans.

My list of possible culprits,
DME relay, (ordered a spare anyway).
Idle Control Valve.
Vacuum pipes wrong, dissconnected.
J tube leaking air after the AFM (the pipe going to the oil filler/AOS looks loose going into the J tube).
Fuel pressure regulator.

Any ideas welcome.

Does sound like an air leak somewhere. Do you have or can borrow a smoke machine? I was struggling with an idle once so I filled up the inlet side with smoke and eventually spotted it leaking out the top of the AOS, wouldn't never have found it otherwise!

Hi, I tried to have a look under the bonnet of my 944S, but the light got bad, also I don't have the evap canister setup that you have. However, I have spotted at least one small error in your vacuum routing. The green pipe from the heater (bulkhead) needs to go solely to the heater control valve near the oil filter. The green pipe is standard on 8V and 16V models, but the 8V heater control valve is located near the bellhousing, so goes straight there. With the 16V models, an extension pipe is used to route all the way around the engine (black tube). So, the connector you lost would have connected these pipes. Looking at the typical vacuum routing it seems that the brake booster check valve goes to a T piece, this in-turn connects to the orange heater pipe, and then to the vacuum reservoir. I don't think your connections are quite right there either, as I cannot see where the reservoir is actually getting vacuum from. If the reservoir is out of circuit, this could cause problems. Also, the evap valve will not be getting vacuum. I will see if I can find a clear vacuum routing diagram, or have a look tomorrow under the bonnet for more clues! Hope this helps a bit...

Here is a heater vacuum diagram (ignore the red arrows and numbers), it should illustrate some of what I said above:

Here is the diagram for the evap charcoal canister. Have you connected the thermo valve (21)? I cannot help too much here as I don't have this setup on my 'S':

Vacuum pipes are 23, 24, 25.

Hi. Thanks for your input rhett.

I'm currently sat in my engine bay tracing what I have. I did have the brake booster in the wrong T piece but if I connect the green heater pipe directly to the valve near the P/S reservoir this will leave the pipe going to the evap in the N/S inner wing open at the second T piece.

I'm thinking maybe the green pipe should go into the T piece now but I'm sure it had a rubber connector on it. I have no other spare vac pipes so this must have gone here.

I have taken my J tube off and one pipe, going to the oil filler, had almost broken off. I have removed it, cleaned it up and re-bonded it back in place so hopefully this cures the running problems. I'll let the bond set before fitting it tomorrow.





Also found a split where the bracket attaches.



The DME relay also arrived but I will run it before I fit it to see if it's cured beforehand to eliminate the DME.


EDIT to say I can't find where this item number 21 is on the second diagram?

Hi, Yes, the broken pipe and the crack in the tube will definitely cause problems! ...so well spotted and hope the repair works. I have had a look at the vac diagram and the green heater pipe must only go to the heater valve over by the PS reservoir. That is because it is an output to that valve, it must not go anywhere else or be 't' connected, as it needs to be a variable vacuum supply to the valve to operate it. Regards the thermo valve (21), it appears that the only diagram in the 944 parts manual to show the evap system is the diagram I posted. However, it doesn't seem right for the 16V models. So, I had a look at the 968 diagram for a clue, and that is closer to what you have. It seems there is no valve 21 on the later 16V models, and perhaps the system fitted in your car is a bit of both designs..

Anyway, are you sure that there is not another regulator down near the AOS pipe? The diagram I posted shows item 17 (a bleed control valve), and the parts list definitely states that this is fitted to the 16V engine. I just get the feeling that we are missing at least one important vac connection...as otherwise we have too many t piece connections. As I mentioned, I do not have that system fitted to my 944S, and the 924S 8V engine is exactly as shown I the diagram I posted.

Perhaps someone with a 944S and the evap system could confirm the vac routing????

Right..had a real long think about this and studied the various diagrams and photos, also looked at some photos that I had taken when working on my car too. I think the following diagram should be about right, it seems logical and takes into consideration all the t pieces and the 'missing' straight connector too. I am assuming that item 17 is not fitted.

(1) is the reservoir, this definitely connects to the first t piece (2), the orange pipe to the heater bulkhead (3) and the brake servo (9). This is confirmed in all the vac parts diagrams. The green pipe goes into a straight through rubber connector (you might have used this on the fuel regulator??), it then connects to the black extension pipe that goes to the heater vac valve, as shown. I have confirmed this on my car, and the diagrams.

The fuel regulators are connected together with a t piece (6) that also gets vacuum from the inlet manifold. However, you must then put the other t piece (shown in the photo) onto the regulator (4), as the shape of the t piece is moulded to fit...see arrows. The last connection is to the evap valve (8).

With this configuration, the reservoir is in circuit, the heater gets a vac supply, all the fuel related valves get a vac supply from the inlet manifold, and the heater valve gets its independent variable vac supply from the heater unit.

Hopefully that will all work... . However, if there are owners out there who could confirm against an actual physical configuration, that would be good!

Thanks again for taking so much time again, I do think I need another 944S with HVAC system as I think that pipe that runs from the PS res, under the inlet manifold and to the right side T piece is correct, I can almost say this with 100% certainty from when I stripped it down because I didn't ever move the two T pieces on the bulkhead but now seeing your drawing and what you say does make sense, its making me doubt myself.

If the engine runs fine the way I have it set up and now I (should) have no air leaks after the AFM I will leave it as is but if not I will give your layout a go as it does make sense what you are saying.

I think I owe you a beer either way.

Rhett, I didn't get chance to work on the car today but did sit looking through and zooming into my million engine rebuild photos and found two where I think you have proved me wrong. My memory must have faded in the two months of waiting for the engine to go back in the car.

The first one does show a single pipe from the green one with a straight through rubber connection, its not too clear as I had to zoom in a lot and I found an early one in the rebuild where I have removed the cam cover and fuel rail which shows the T piece around where the fuel reg would usually sit. This would all match up exactly with what you are saying in your diagram.





I'm hoping I can get it re-fitted tomorrow, so with the now fixed J tube and vac pipe correct hopefully it all runs good again.

Hi...that's all great news, and glad to be of assistance!

Hope it goes well from here on in...

Ran the car today for around 10 miles and it's running sweet as a nut. Hopefully this thread and Rhett'S diagram is of use to someone else in the future .

If you are both still lurking on here, this thread has indeed helped me out.

Reference Rhett's diagram:
On an 1988 944S 'without' the Evaporator
2. is connected to 7. with an inline check valve (keeps the circuits seperate incase of a vac leak on heating side))
9. is only connected to the intake manifold with no take offs