CIS question for those in the know...
 

Why does a 1974 CIS equipped car start hot or cold when later models need the auxiliary air devices?

Don’t understand your question. Early CIS cars use a hand throttle that can also activate a cold start injector to riches the mixture to get the car going. Later cars included a thermotime switch to perform this function.

This web page may be instructive. https://jimsbasementworkshop.com/CIS/CIShome.html

Problem is my 76 is missing the auxiliary air regulator and the auxiliary air valve (don't ask) and it's a pain to start hot or cold.


I used to have a 1974 911S and it had a thermo time switch and cold start injection and a hand throttle that only pulled on the accelerator rod to open the throttle slightly. It use to start fine.

Why does the 1976 911 need all that (except the hand throttle) plus the auxiliary air regulator (heated) and the auxiliary air valve (vacuum) to start?

Why did the early ones start every time but the later one won't without auxiliary air.

Hope this makes a bit more sense.

P.S. I have installed a factory hand throttle.

Missing critical CIS components........
 

psycho,

Why did you install a hand throttle? I don’t think it will solve your problem/s. Is your CSV working during a cold start? PM me if you need AAR and AAV. Keep us posted.

Tony

Hi Tony,

I installed a hand throttle in preparation for a ITB install. Yes the Cold start is working, I've tested it. I need to get it starting better for it to pass some of our rules for registration down here, And it has to pass with CIS and not ITBs. So anything I do to fix it will be temporary.

Frank

Have you checked all of the basics in the manuals?

Things like air plate height, air plate space all around, fuel flowrate, etc. There is a list of basic CIS settings before you even get to the things like control/system pressures. It might be starting with those may assist the starting.

For example not enough fuel flow, or a sticking air flow plate or incorrect air flow plate height would all likely cause a problem with starting, as would your control pressures etc. Get your hands on manual and check each item, until you find a problem, then fix one at a time

CIS troubleshooting.......
 

Frank,

Installing a hand throttle to your engine will not help fix your starting problem. The hand throttle works for CIS motors with TPR (throttle pressure regulator) and micro-switch found in early CIS engines. The TPR was removed in ‘75 if my memory serves me good. And the ‘76-‘77 CIS have AAR & AAV to facilitate cold starting in conjunction with the CSV & TTS & TTV (thermotime Valve).

The parts you need are abundantly available and cheap. Install the needed components and get your car running well anytime of the year. Until you have the missing parts installed don’t expect for a miracle.

Tony

Also, before taking a dep dive onto fiddling with the CIS (other than replacing missing parts), be sure your car is fully tuned (points/cap/rotor/timing/dwell/valves adjusted).

If any of these are off, you will be chasing endlessly to solve your problems.

First off, a big thank you to those that have offered advice. I'm sure I just need to source the missing Aux air parts and I'll be good. I just don't want to spend top dollar on parts that I'll make redundant when the ITBs go on.


Strictly,

I have done all of that. From the fuel pump check valve all the way back. I have a few CIS and Porsche specific manuals relating to it. I have even rebuilt the Distributing unit as it had a failed 'O' ring in it that let fuel flow all the time from one injector when the pump was on. Although it was a while ago. I will go back and revisit the fuel pump check valve and the fuel accumulator although the accumulator is new.



Tony,

I only installed the hand throttle in preparation for the ITB install, not for this starting problem.
I know I need the missing parts and I am not really expecting any miracles.

My original question was why did the early cars not need the parts that I don't have?
I believe that you answered that with the micro switch and TPR. I don't have a micro switch but I do have a deceleration valve. I don't know what a Throttle Pressure Regulator looks like.
Obviously Porsche/Bosch improved the system with Auxiliary Air. Thanks
http://forums.pelicanparts.com/support/smileys/wat6.gif


HarryD,

I have new plugs, points, rotor, MSD6AL, and I've had the distributor professionally rebuilt, new clewert leads and new blaster coil. the epoxy filled one. I did the tappet clearance and the cam timing many years ago but since that adjustment it has been driven only 100 miles so I'll assume they are still ok.

It idles well at 900 +/_ and pulls like a train when I get on it. I have taken it to 6000rpm so far and it doesn't have problems getting there.

I just need the missing parts.

Cheers,
Frank

G'day Tony,

I just researched Throttle Pressure Regulator and I definitely don't have one. In fact I never heard of it begore. Probably because I've never needed to:D

But this is the difference between the early cars and mine.

I better start shopping.

Cheers,
Frank

Picture will help........
 

Frank,

Do you have a picture of the back side of the motor showing the CSV, Decel valve, and throttle body? The 73.5 and ‘74 911 CIS motors have TPR when they left the factory. If your motor does not have a TPR, someone had removed it.

Tony

http://forums.pelicanparts.com/uploa...1639870375.JPG
All of this to replace the hand throttle. I would keep your hand throttle. Makes for a much more simple engine and less vacuum leaks to deal with. Plus that stuff rarely works right after all these years anyway.

Tony,

My current car is a 1976 so it may have never had it. My car originally had all the Aux Air stuff but it was lost/ misplaced/ thrown away many years ago. This has been a 28 year project that's very close now. Just the final teething problems.

I know that I have the cold start valve with intermediate piece that is 'not' open to the hose barb. That's the barb that the Aux air feeds into. I just picked up yesterday an old 'Top hat' that has the port for the Aux air.
I just need to find an Aux air reg and an Aux air Valve.
And also drill through that barb so it can feed into the vac side of the air box.

All this to make it compliant for our registration requirements. Once registered the CIS comes off to make room for the ITBs

Cheers,
Frank

G'day Don,

Unfortunately I need this to pass our registration requirements.

After It's registered I can get rid of it all :D

Cheers,
Frank

Holiday spirit.........
 

Frank,

Sorry for the mix up. I had it backward. You had a ‘74 and now a ‘76 CIS. I have boxes of CIS components (AAR, AAV, decel valves, aluminum vacuum tubes, etc.) that I will never use and just collecting dust. If you could not find them locally and willing to pay the shipping cost, I will give some parts to you for FREE except the AAR.

Make list of parts you will need and wait for Santa Claus. Happy holidays to everyone.

Tony

G'day Tony,

That's very generous of you. Thank you for the offer.

As far as I know, I require 5 parts:
The top hat. I have.
The intermediate piece. I have.
Aux air Reg
Aux air Valve
and hose to connect it all up.

I'll PM you.....

Hi Tony,

I have these:

http://forums.pelicanparts.com/uploa...1639890500.jpg
http://forums.pelicanparts.com/uploa...1639890500.jpg
http://forums.pelicanparts.com/uploa...1639890705.jpg

and although from a 924turbo, this:

http://forums.pelicanparts.com/uploa...1639890592.jpg

The pipework I can sort out down here.

so i probably need just this:


http://forums.pelicanparts.com/uploa...1639890835.jpg

Regards,

Frank

Needed CIS components..........
 

Frank,

I have more AAV than I would ever need. It is surprising that you don’t have one because this AAV is abundant and easily available.

http://forums.pelicanparts.com/uploa...1639925336.jpg

So you don’t need these:

http://forums.pelicanparts.com/uploa...1639925696.jpg
http://forums.pelicanparts.com/uploa...1639925696.jpg

Will go to the Post Office tomorrow (Monday) and get back to you ASAP regarding postage cost. Try again to ask around because the AAV is abundant in supply. If you are not able to find one, I have plenty to give away.

Happy Holidays.......

Tony