924Board.org

[maybeoneday]

Hi again,
If you read my last post you will know I aquired a 77 NA 924 with a blown head gasket and I have been having a few issues getting it going after doing the gasket.

I was reading the Bosch K jetronic manual because my first look at this system almost killed me and I thought I better work out how it all worked. I have just noticed something and I thought I should ask about it.

There is a rather large boot on the air metering plate that runs to the inlet manifold via a plastic pipe and another boot. Off this boot (the one on the metering plate) there is a branch. On the car before I did the head this branch was plugged close to the boot with a screw (it ran nowhere and it was blocked off). When re-doing the piping I decided to replace this boot and reinstate the branch to where it was supposed to run. My investigation showed that this went to a canister thingy (I am sure this is the technical term) that at the time I was unsure about what it did. My reading about the system makes me think that this is an auxiliary air valve that provides more air at start up.

So I am guessing that if this branch was plugged then something was probably wrong, however the car did still start at this point (even though it made milkshakes in my sump). Could re-instating this branch be causing me problems in starting the car? I am thinking that if this valve was stuck in position then it would either perform the same as not having one (which is the same as plugging the branch) and therefor it should not be the cause of my problem, or help in starting by giving me the right air mix at start up but then cause issues when the car warmed. Is this theory correct? I am guessing that it is better to get this thing fixed rather than leave it how it was, right? Is this really what I think it is, the auxiliary air valve? If it is, I am guessing that a site search should bring up most of the answers I need in regards to the problems it can cause and the best solution to fix it.

Thanks again, learning about this thing is a little harder than I thought it would be, but it does bring to light some really beautiful engineering solutions and I am starting to appreciate the car a little more. I always liked them as a kid (this one is as old as me) but the 911 guys tried to talk me out of getting it when I mentioned it to them. I am glad I didnt listen and I went ahead and got it.

[larchie]

If you are speaking of the auxiliary air regulator (valve), ...

... when the engine is cold the valve is open and air passes from the boot through the valve to the air intake. With ignition on the valve closes as the car is runs. So if the connection to the auxiliary air regulator is plugged permanently, it would not be the same situation when starting.

In the following diagram item 5 is the auxiliary air regulator and the connection in this diagram appears to come off the air mass meter boot:

But on my '79 the channel off the air mass meter boot is plugged and the connection to the auxiliary air regulator (valve) is off the intake boot:

If my memory is correct, the original air mass meter boot had no such connection, so my guess is that this closed off branch is designed for a later CIS design.

See the the parts in 924 PET Manual Main Group 1: Engine, SG 06, Illustration 106-00 on the website for Porsche Part Catalogues: Genuine Parts Catalogue

[Ozzie]

you may be talking about the connection going to the hose for the brake booster.
It has a Y connector on the hose and connects to the intake manifold near the CSV as well as the booster.

the other boot near the throttle valve also has a take off which goes to the AAV

Most of your gear might be ROW specific as USA models had lots of extra vacuum lines.

check illustration 604-05 in the above PET part 22
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

[scm924s]

If I read this correctly, the outlet from the boot that fits onto the fuel distributor was blocked off on your car. As your car is 1977, it wouldn't normally have this outlet, this is for the crankcase breather on later cars. On the 1977 this breather goes directly into the air filter box. Possibly someone has fitted later trunking and therefore blocked this outlet off.

The brake booster connects to the alloy plenum chamber.

As has been mentioned, your car is likely to be euro spec.
_________________
1984 n/a Ruby Red Metallic
1988 924S Guards red- sold
1986 924S Guards Red - sold
1984 n/a Black - sold
1980 n/a Le Mans#1 - sold
1980 n/a Le Mans#2- sold
1977 Martini - sold

[maybeoneday]

I am just going to take a picture. I will post it soon.

[maybeoneday]

Hi again,
Here is a photo of what I am talking about. So its not what I thought it was but thanks for the photo of the AAV coz now I know what that is. I think ozzie may be right because one hose goes to a t junction in the booster set up and another goes to the inlet manifold. anyway have a look at the photo let me know if this is plumbed right and I'll keep reading about this system and see if I can ever work it out.

[larchie]

That would be the Deceleration Valve or Vacuum Limiter which I thought would be only on the early manual transmission 924s. Some people take it off completely supposedly to save on weight. (See link below for explanation.)



In the image you provided, he looping hose from this valve to the air mass meter boot would normally go instead to the center plastic piece between the boots on the manual transmission 924s:



And the branch on the air mass meter boot would be plugged.

Whether a Decel Valve would help on your '77, I don't know because on the '77 automatic I don't think there originally was a Decel Valve, so imy guess is that it might have been added by an earlier owner.

This page might be helpful in deciding what to do: CIS Deceleration Modification which should be appropriate for your 924.

In a post on the 924board.org Smoothie writes:

[scm924s]

Interesting, never seen that before, my Martini has certainly never had that fitted.

Reading some of the information, it seems to be a Turbo specific part?
_________________
1984 n/a Ruby Red Metallic
1988 924S Guards red- sold
1986 924S Guards Red - sold
1984 n/a Black - sold
1980 n/a Le Mans#1 - sold
1980 n/a Le Mans#2- sold
1977 Martini - sold

[larchie]

[maybeoneday]

great info thanks I have no idea what it is doing there if it is not supposed to be there. This car has only had 2 owners the guy who I got it from and his fathers friend. I am assuming this is true because there was no reason to lie about it as I was told after I had agreed to take it.

I also think I found my starting issue, I set the flywheel to the 10 line not the 0 because I can hardly see the marks, Anyone have an easy way to make these more clear without adding any more paint lines and dots.

[larchie]

[jason c]

I would clean the timing mark areas with a wire brush & solvent on a rag then repaint the marks. Different colors for each. The problem with adding non factory degree marks with the flywheel on the car is getting the marks accurate. Furthermore, there is no reason to add additional timing marks. If you use a timing light with a built in advance you can compensate for whatever degree you want.

[larchie]

[jason c]