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AndrewCologne AndrewCologne is offline
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Join Date: Aug 2015
Location: Cologne / Germany
Posts: 85
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CIS removed - got some questions

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
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911 SC 3.0, 1982, black, US model

Last edited by AndrewCologne; 09-13-2016 at 08:51 AM..
Old 09-13-2016, 08:48 AM
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