Cis 201

William Miller · 06:13 AM

Jim William's "Renlist CIS Primer" is a great introduction for those of us with CIS cars. I am very intrested in expanding the content of the "Primer" with the collective knowledge of this board.

Thus the subject of this Thread CIS 201.

I recently reviewed the primer for updates and I have read a lot of books, articles, posts as well as asked a lot of questions.
There are a lot of things still to be discovered that I have not seen anywhere.

With the basic theory down I am intrested in P-car specific tuning tips and tricks as well as modifications to improve performance and drivability. Mine is a 83 ROW with K-basic. Along with the 79 and earlier US owners, I have to rely on tweeking and tuning to get the best out of our systems because we don't have the luxury (some may say constraint) of a closed loop system.

Please include Lambda System ideas as well because this should be for all CIS owners.

I'll do my best to answer questions about things I know about.
Please add any info or links you like.

A few things to start it off:
What things are adjustable on CIS (Maybe more detail later)
K-basic: (and maybe K-lambda)

System Pressure (on the side of the Fuel Distributer)
Warm Control Pressure (Inside the Control Pressure Regulator)
Cold Control Pressure (Knock the plug)
Basic Mixture Adjustment (3mm allen on top of Mix Unit w/gas analyzer)
Flow plate rest position (Below arm)
Idle Speed (by-pass screw on throttle body)
Old style vacuum limiter (adjust nipple on top of device)
Adjusting flow on fuel distributers
Adding Air/Fuel Ratio Meter (Narrow and Wide Band)
I have herd the Thermovalve was used for different things on different versions of 911's Why? This is a porsche specific part.

K-Lambda:
Latest technology to monitor and manipulate fuel delivery.

I'm sure there are more please fill in. I know most about my car.
Any info posted here will help a lot of people!
Thanks!

"Renlist CIS Primer"

aigel · aigel's Garage

Where is the primer located? I need to read that first.

dbraunsr · 03-09-2004, 07:07 PM

Here's the link.

http://members.rennlist.com/jimwms/CIS/CIShome.html

Randy Webb · 03-09-2004, 08:40 PM

I would just read the yellow Bosch tech manual on the system.

HarryD · 03-09-2004, 09:36 PM

Wayne can help you out. Look here: http://www.pelicanparts.com/catalog/shopcart/BOOK/POR_BOOK_bkptec_pg3.htm#item16

William Miller · 03-10-2004, 06:26 AM

Here are a few of the references that I have read on theory along with other stuff. They all are lacking in detail on Porsche specific info, or in what I would call advanced theory, tuning and adjustment.

I have:
Porsche Shop Manual
Porsche Parts Manual
Factory Spec Book (81-83) Little spec book
Haynes
Bently Service Manual (for SC's)
Anderson's Performance Handbook
Probst's Blue Bosch Fuel Injection & Engine Management (Has this been updated?)
Aird (Robert I think) Bosch Fuel Injection Book.

I see 2 more books on Pelican that I don't have and i think they may be more of the same.
Solving Bosch Cis Problems (Webber)
Bosch Auto Handbook (Blue)
Does any one have these and do they go into more detail.

I am intrested in more detail or specifications on tweeking the CIS.
How are fuel distributers flow tested and adjusted?
What effect does changing the rest position of the metering plate have (If any)
Is there a way to slow down fast idle at start up?

Some of these are known by very few people that know the secrets.
My intrest is in expanding that knowledge base and learning for myself.
If anyone has these books can you tell me if there is more info about these few subjects as well as those listed above?
Thanks!

cmonref · 03-10-2004, 05:37 PM

From your question:

"Is there a way to slow down fast idle at start up?"

... are you asking how to reduce the idle speed during warmup after a cold start on a cold day? In other words, how to adjust the Aux Air Regulator?

aigel · aigel's Garage

I just got the Probst blue book. Nothing special in there. The author discourages any performance mod and only talks about racers doing it. No info whatsoever on how to tweak the CIS without an instant warning about safety or loss of driveability. Very disappointing. May be the FI system more than the book, of course.

I am mainly interested in the role of the lambda sensor and what happens if you undo it. Sure enough the book only talks about how the lambda sensor puts you back into the stochiometric region regardless of mods. DOH!

George

William Miller · 03-11-2004, 05:14 AM

Hi Brian, it's been a while.
I finally located an 83 ROW Fuel Distributer and things are much better.
You are correct about the Aux Air Regulator. I have set my timing based on the John Walker method. It is somewhat advanced from the factory spec at idle now so the engine spins faster at cold idle. At times I've seen it 2500-3000 rpm. It's annoying, but also probably not good for a cold engine. It also stays at high idle for longer than needed. There are a few variations on that part and maybe a different variation is what I want. Otherwise maybe there is some sort of restrictor that I can put in the line to limit the size of the full opening. Anybody done that?

George, I thought the blue book was great resource to give me the understanding that I have now about CIS. Unfortunately it's not Porsche specific and as you stated falls short of going beyond what bosch wants their end user to know.

One reson I started this thread is because I believe the collective knowledge here goes way beond that.

cmonref · 03-11-2004, 05:44 AM

William: followed your progress in getting your fuel distributor sorted out. You are on quite a roll!

To adjust the AAR, take it out. Remove the 4 rivets that hold the large face on. Remove the face. The innards are intuitive, with a large disc with a hole in it that generally aligns with the air patch thru the AAR. A bimetal spring turns the large disc, varying the size of the air path provided by the hole in the disc. On mine, with uncomfortably high idle speeds (2000 rpm) when really cold, I realigned the mechanism to cut the air path down to --guessing here -- 25% of the original size, as measured at around 30 degrees) I religned it in stages and found that more than 50% reduction was required to have an effect on the idle speed. (Proof that it does not take much air to have a significant effect on idle speed -- so there is no such thing as a "small" vacuum or intake leak in CIS!)

So that set the idle speed at a more rationale value. The secondary effect was that the warmup period was significantly reduced. The time of warmup is the time to turn the disc to shutoff the air flow, and if it STARTS at a less-wide-open value, it gets closed much more quickly.

Put the face back on with smallish (maybe 4 mm) bolts, washers, and nuts. I have no air leaks after several iterations of disassemblyand reassembly.

This problem of high cold idle and long warmup times plagued CIS into about 1981, when Porsche put a larger heating element in the AAR. I do not know how to tell the difference 'tween old- and new- units.

William Miller · 03-11-2004, 05:55 AM

Thanks Brian, that's exactly what I was looking for, for me, and this thread. I have what I think is both an old AAV and a newer one. When I get the chance I'll survey them (Inside and out) and post results.

We had a few posts on the Warm control pressure adjustment.
I'm going to post a link here when I get a chance.

Anyone else have some things they have tried!
Thanks again Brian!

cmonref · 03-11-2004, 06:54 AM

Keep up the good work! Interesting stuff.

What we are talking about here is the AAR -- Aux Air Regulator. The AAV -- Aux Air Valve -- is the english-muffin-lookin' device mounted behind the fuel distributor The AAV provides start-up air then closes immediately upon engine start.

William Miller · 05:47 AM

I hit the wrong key. I ment AAR. I was thinking of an alternate plan to slow down the fast idle. I'd like your thoughts. What about putting some kind of restrictor in the hose that comes out of the AAR. This would be something with 2 barbed fittings. I could probably find a small gass (natural gass) valve with a thumb turn which would allow me to actually adjust the fast idle. Most of these are ball valves. (Bassically a ball with a hole drilled across it.) The ball is inside the valve body. When open the hole goes straight thru. when closed the hole is turned 90 deg.

This would not effect the duration of the fast idle, which I wouldn't mind if it wasn't so fast.
What do you think?

William Miller · 03-12-2004, 06:19 AM

FYI, to those that subscribed so far:
I edited the first post and inserted the link to the "primer"
I also deleted some of my redundant replys -- bumps etc.
I hope to continue to eliminate extra stuff.
And condense it by putting links in the first post.
Brian do you recall the thread about Adjusting warm control pressure?
Thanks for the help everyone!

William Miller · 03-12-2004, 01:06 PM

Bump for afternoon and west coast guy's.
I know your out there, please share your knowledge!

cmonref · 03-12-2004, 06:16 PM

William,

I toyed with the idea of putting a restrictor in the air lines that serve the AAR, but chose not to. The lines in my '80 Euro are aluminum except for a few inches right at the AAR. I did not want to mess with that setup.

After studying a section view of the AAR, I chose the "adjustment" route. In retrospect, it was the right choice, and I would not recommend a valve as you suggest.

I remember the "warm adjustment" thread, but also recall that most of the practical stuff and details were shared via private email. You touched on it in another thread later, but not to the detail that you and I went thru.