CIS removed - got some questions

[AndrewCologne]

Hello all,

a good friend of mine got some problems with his 911 2.7 from 1975.
The exhaust gas recirculation has been already removed in the past.

The idle is very, very rough and furthermore backfiring makes the engine unable to run.

What we tested:

- System pressure = ok
- Control pressure = gauge also here says its ok but hard to check as the idle is almost not possible
- All injection jets/nozzles do output the same amount of fuel
- Valve clearance is ok
- Ignition timing ok
- Ignition points = ok

So I thought lets do the whole job and remove the CIS to check all plugs, rubber, pipes etc.. Beside this its good for cleaning everything and replacing the known three seals on top of the engine.

After removing we recognized that the removal made sense as the connection of the crankcase ventilation tube was already "a bit" leaking. But ... for sure thats not the reason why the engine won't run normal without backfiring.

Then I saw a very strange type of tube connected to the black air housing below the throttle unit.
And that tube is ... open, and beside this metal tube there are two disconnected hoses as well.
See my pictures below. So ...

What was this tube (red) and these hoses (green) good for? I think we should seal/close them as this could result in a big problem with false air, correct? And so maybe that rough backfiring idle comes from?






Also after the CIS was removed there where a disconnected dirty electric plug (Plug 2) lying around.
Do you know where this Plug 2 belongs to? It seems odd to me that it wasn't connected.




Many thanks for your help!
Andrew

[timmy2]

Need the colors of the wires in the plugs to correctly identify them.

[75 911s]

Hi Andrew,

The pipe coming off is the EGR valve pipe. The two vacuum lines also belong to the EGR valve.

From my understanding, exhaust comes out engine into the thermal reactors, then into the heat exhchangers, then the muffler which then some of it goes into the EGR filter, which then goes up to the valve, and back into the intake via that metal/rubber line.

Of course the thermals are probably gone...do you have 3 into 1 Bursch headers that go over to the stock heat exchangers? or do you have backdated SSI style heat exchangers that have the heat boxes and headers all in one?

The other plug I'm not sure. Did you disconnect the heater blower motor or was it intact when you took the CIS off?

I'm skeptical of the EGR being the culprit for your issues. When you get it put back on and sealed up, if you still have the problem, I would check the WUR, and then the mixture as it may have been messed with making it too lean or rich.

The mixture is super sensitive from what I've read. I wouldn't mess with it unless it's a last resort.

[75 911s]

Also, does your throttle lever work next to the E-Brake? You have to pull that so that idle is at 2k upon first start, then the WUR kicks in and the idle drops to about 1500, then you drop the lever and idle goes to a normal 900ish

Here's a pic of where the vacuum lines and EGR intake tube go

[boyt911sc]

Originally Posted by AndrewCologne

Hello all,................................

Also after the CIS was removed there where a disconnected dirty electric plug (Plug 2) lying around.
Do you know where this Plug 2 belongs to? It seems odd to me that it wasn't connected.




Many thanks for your help!
Andrew

Andrew,

This is where the plugs go:

Plug #1...............AFS (air flow sensor) 2 wires (1 brn, 1 brn/red).
Plug #2...............AAR (auxiliary air regulator) 4 wires (2 red/wht & 2 brn).
Three-wire(?).......CSV (cold start valve) 3 wires (1 red/wht, 1 yell. & 1 yell/blk).

Plug the EGR hole under the air box and the two (2) vacuum hoses too. You don't need them anymore since the EGR has been removed. Keep us posted.

Tony

[timmy2]

No AFS on '75, started in '76.
Likely the CSV and AAR only.

[boyt911sc]

Originally Posted by timmy2

No AFS on '75, started in '76.
Likely the CSV and AAR only.

Mistook it as OP's SC. You are indeed correct CSV and AAR only. That's why I have a (?) for the three (3) wires in his picture. Thanks for catching the error. I actually checked and compared them to your new wire harness (Paul Z's) sitting in my basement.

Tony

[timmy2]

No worries Tony,
Wire colors and configurations changed year to year back then. Probably only one yellow and a red/black to the CSV connector. The yellow is likely Doubled back from pin one in the 14 pin connector over to the TTS and then to the CSV as a single yellow.
They weren't consistent at all as they changed and learned the best ways to do it!

The reason I asked for the colors instead of telling him what they should be is to determine if the correct year harness is installed!

The joys of hand built cars and previous owners.

[AndrewCologne]

HI all,

first: thanks for all your feedbacks - I really appreciate it.

- We will make some other pics from around the whole CIS, so you can see exactly where Plug 1 was connected to
- We also will have a look at the wire colors of the Plugs and will tell you
- This CIS doesn't have an Auxiliary Air regulator/valve - and the car has been build in June 1975, maybe thats why

So it seems we are dealing with a very early type of CIS
http://cis911primer.com/pages/descr_basic.html

Best regards
Andrew

[timmy2]

Ah, learned something today. The car is a euro version, so it doesn't have an AAR.
The engine harness would have been wired for both US and Euro markets, so it would have the AAR connector installed, and not be used. (Porsche only built one style of harness each year, they just didn't connect what wasn't needed)

[AndrewCologne]

Hello,

this CIS here belongs to a US 911 2.7 model, not Euro.

I made some new pictures.

Below you can see the colors of the wires from each plug.
(Plug 1 gots yello-beige and red, plug 2 both in brown)
Maybe with that you can say where the other plug 2 belongs to.





Here below you can see from which port plug 1 was pulled from


Also above there are two parts where I would like to know if "theres missing something" and "what was that part good for“ where they applied a plug and the the rings.



Also I would like to know to which part of the CIS this hose goes to ?






And last but not least we checked the air box where I thought the main issue/problem of the uneasy idle comes from and the hole very below which wasn't closed/sealed IMHO definitely needs to be closed as otherwise it would result in a mega false air input.
For closing/sealing used a plug normaly used for radiators which fits perfectly.




So we only need to know the infos of the plugs and the hose above, then we will re-install the CIS and .. see if the "false air" issue above was the guilty one.

BTW: WUR also works perfectly: pressure ok and the restore shows about 37 ohms IIRC.


Thanks a lot for your assistance and BR
Andrej

[ADDvanced]

What do you mean by radiator plug?


Sent from my iPhone using Tapatalk

[75 911s]

He means an off the shelf radiator drain plug (brass from the looks of it) used to plug the EGR input port on the CIS box. Likely you can pick up one of these from your local auto parts store. Don't forget to plug the two vacuum lines on the Throttle body as well. Unmetered air is the enemy of good running CIS.

Also no one answered Andrej's last question so I will for posterity since the thread was bumped. That last hose in question is an overfill drain hose. One side connects to the back of the CIS air box via a plastic nipple, and the other connects to the shown plastic nipple that sticks through the back of the engine tin. On the other side above the trans is a plastic diaphragm (older ones are metal) that retains overflow oil and has a gravity orifice at the bottom where it drips oil out onto the road (on purpose) lol. I'm pretty sure they did away with it in 78. It looks like a condom hanging down behind your engine.





Here's the older metal drain tube:



Here's the drain hole at the back of the CIS air box When you overfill oil is pushed out the top of the fill tube and to the curvy hose that connects to the side of the airbox on early CIS cars:



Showing how I capped off the EGR vacuum lines on the TB:



A lightweight simply aluminum bracket I made to replace the heavy EGR metal bracket that also sticks out and makes changing spark plug #6 a pain.



The original EGR bracket:



The EGR plug using an off the shelf FLAPS (Friendly local auto parts store) radiator drain plug.

[ADDvanced]

So my question is... the hex fitting at the bottom of the airbox. Do you remove that to install the plug? Or do you thread the plug into that?

I ask because I’ve tried in threading it and it seems like I will break the airbox.


Sent from my iPhone using Tapatalk

[ADDvanced]

Woah! Impact zipped it right out!

Also, for future reference my 77 also has that little plastic condom oil drippy thing. How does that not cause a vaccum leak? Wouldn't air get sucked into it?

Off to get a plug from FLAPs.

[boyt911sc]

Originally Posted by ADDvanced

Woah! Impact zipped it right out!

Also, for future reference my 77 also has that little plastic condom oil drippy thing. How does that not cause a vaccum leak? Wouldn't air get sucked into it?

Off to get a plug from FLAPs.

The filter area is at atmosphere where the drip nipple is located. It is not under vacuum but rather atmospheric condition.

Tony

[ADDvanced]

Makes sense, it's before the throttle body so yeah. Duh. Picked up a 94-01 dodge ram plug from auto parts store, looks like the same threads.