nick_968

I currently have the intake off and am going through all the vacuum pipes and checking the install done by others. One thing I have found is the vapour control valve has been removed and what looks like the vacuum pie that connects to it from the firewall is just hanging there open. Should this line from the firewall now be connected to something else or is that firewall connection now redundant? It seems strange to have an open vacuum pipe and I am wondering if this is could be causing my hot idle problems.....

The other line from the firewall is connected up to the main vacuum system around the engine bay.

mikeyoman

Ok, sounds like your vacumn lines are in a bit of a mess, the attached pic may help you some.
At the bulkhead, the top vacuum line is the vacumn supply for the heater assy, and connects to the black (or green) vacuum reservoir tank via a tee. This reservoir also connects to the Blue check valve via the same tee.
The lower pipe at the bulkhead connects to the water heater valve located down at the rear of the engine ( unless it's an S2 then it's somewhere near the rear of distributor I think). This vac pipe activates the hot water valve when you select heating for the cabin.
The 2 vac lines to the fuel vapour purge valve connect to the manifold via the temperature switch and fuel rail vac lines, see attached.
You'll need to block any spare open vac lines attached to the engine or you will get problems.

BTW - I found a lot of the heater solenoid valves leak when old, not too much but they do fail. You'll need a Mittyvac or similar tool to see if they hold their vacuum. Not a bad idea to invest in one of these beauties anyway.

nick_968

Thanks Mike. As far as I can tell I have everything connected up in the main circuit with the exception of the fuel vapor purge system, which is gone and all three lines coming off it are gone. I also have one line coming off what looks like the heater valve connection coming off the bulkhead which has nothing connected at the other end, just a loose vacuum line. The long line looks ike it was heading over towards where the vapor purge system used to live.....

I dont have any problems with my heating system either but the second line coming out of the bulkhead is definately loose. I will have another look at the layout when I get home tonight and re check the diagram to confirm.

nick_968

Well I have solved the mystery of the missing vacuum connection, there is no heater control valve on my engine. The two pipes that come out of the bulkhead are solid with no connection for the valve anywhere. One comes out of the back of the head and goes straight to the bulkhead, I assume this is the original 968 pipe. Then the other one comes out of the bulkead, connects the the metal hardpipe running along the top of the headers and into a short rubber pipe into the waterpump. Not sure why this happened or why I wasnt told it was removed, although I have never noticed it till now. Could it be that when the heater sends the vacuum control to the heater valve I then have a vacuum leak back to the main vacuum system which will affect the engine running/ idle? I think I will block off the vacuum line temporarily and when I get a chance I will install a new valve in the 968 location by the waterpump.

The only thing I was not sure about is whether the water line that comes across the headers is the right place to put it, but I guess it must be as my original lines must have run that way before the original 968 engine was removed.

mikeyoman

Sorry, didn't spot it was a 968, but I guess they are similar to S2.
968 vac line pic attached.
As you say, when heat is requested the open pipe that should go to the heater valve may allow a vacuum leak through the heater vac solenoid.
The location of the heater valve for a 968 engine is just behind the cam housing, see attached.

nick_968

Thanks for the info Mike, I think I will go back to this arrangement. Out of interest on the 944 turbo does anyone know if the heater valve goes on the same water line, just closer to the bulkhead, or does it fit on the other line coming from the metal elbow coming out of the head? i.e. can it go on either line?

968 GUY

probably since the base car is a 968,you should arrangr the HCV and vacuum actuation the same way as on a 968. Do you have a PET Cat. downloaded for the 968 and 944T?If not, you really should, helps me out a lot. The 944T does not use that valve, at least not in the same way, there must be a valve under the dash or something.

Ken

nick_968

Thanks, yes I have PET I use it all the time. I was planning to go the 968 way but when you have a car that is half/ half it always pays to check all the options and configurations before you decide which way to go so at least you understand why and where things are going.

mikeyoman

Heater valve on a 944 is at the rear of the engine on the other pipe.
Can't see it matters which pipe it fits too. If it is not fitted I guess you have hot air in your cabin all the time ?

Thom

For what it's worth all 5 factory 968 turbo S I have seen didn't have the heater valve near the water pump like 968 NA, so I would guess they have the 951 set up, with the heater valve above the clutch bellhousing, head side.