CIS Idle Speed and Mixture Setting Without an Analyzer

[MotoSook]

This is a CIS engine. If your engine looks like this, then someone swapped the 3.0 (or heaven forbid a 2.7) into the 1984.

[William Miller]

Originally posted by Macel
Well it seems to me like the idle mixture setting isn't quite as important to fine tune - I'd be more concerned if I were leaning it out too much under higher revs.

I agree. (Except for the emissions test when that comes arround.)

I was quite educated on my ROW 83 CIS. I even did a little tweeking while barrowing an LM1 from a friend. This was a k-basic system without the O2 sensor, control unit, and frequency valve.

Except for in the warm up period (Control pressure lowered)
The mixture is varied, based on air volume, and the 3 different angles in the cone of the air flow meter. In the idle range, the shape of the cone is almost verticle, It then flattens out and near the top it get's steeper again. In addition to this the Control pressure regulator reduced control pressure as manifold pressure increased (Vacuume drops when you mash the go pedal).

When watching the LM1 you could see the mixture changing in relation to these features doing their thing. I have to believe that the initial idle mixture adjustment has an effect on the mixture in the "higher than idle" air flow.

What I saw is the mixture was arround 14:1 at Idle, then leaned quite a bit at light crusing and ramped significantly richer as the rpm increased the air flow and the plate was in that upper (steep) area of the cone. (I recall that that started in the 4000-4500 rpm range and the mixture got as rich as 10-1 near 6000-6500.

Besides those few days I never had the oppertunity to tweek the system further. (I'm not sure it needed it and maybe it was designed to do juat what I saw.) I guess I could have tweeked the system pressure and warm control pressure so that the idle was not too lean while the high end was not too rich. I'm thinking that if I raised the control pressure a bit I could have found that sweet spot.

Now this system was not as sofistocated as the lambda control, but I'm sure Porsche knew that and continued to tweek (hopefully improvements for performance) the k-basic system in the ROW cars until 84 with the Montronic cars.

So, I'm wondering if the basic setting is just as important in these upper rpm / air flow ranges on the lambda cars?

[Macel]

The pictured air intake is totally different. Ours has an air box with a square shaped air filter that lays right across the opening. The ?distributer? sits on top of that, and the hex slot is right next to the ?distributer?.. I can't really describe it better right now. I may be wrong on the year of the car too. I'll look at it when I get home.

[MotoSook]

The last picture I posted is the CIS induction with the airbox cover installed. There is a rectangular air filter that fits under that cover (the plactic cover with snorkle on the end of it).

I suggest that you and your father do a little more research into this before you adjust anything else. Folks who do not understand CIS or any other induction generally create more problems for themselves when they start to adjust things without understanding the effects of that action.

[Macel]

Sorry I was looking at the first one you posted souk.. The second one is the one ours looks like

[MotoSook]

OK. So you have a CIS engine.

Now read this thread:

It's that time of the year AGAIN! (CIS)

[Gunter]

Bill:
Interesting observations. If you set it too rich at idle to compensate for different O2's at higher RPM's, the Lambda system will star too hunt.
Macel:
There are differences between SC engines. Some have Lambda.
What is the engine number?
You'll find it on the bottom of the fan post stamped on the engine case.
Use a light to find it. Something like 930/07 or 930/16.
We can help you undo the damage.
What year? What engine number?

[724doorE]

Alright Souk, its been awhile, but I feel the need for one of my cars to trun a wheel. I'll be using all of your references/info to get my purple 72T running shortly I hope. I have flushed the lines and put a cleaner tank in it. It ran a little when I bought it a few years ago but wouldn't rev, coughing and sputtering. In retrospect that was probably due to bad gas as the tank look like the bottom of the ocean and the gas was red/brown filthy, heack it didn't even smell that much like fuel anymore so was probably a mix of fuel and water. Anyway, I am hopeful of getting it running since I seem to be taking 40 years to put the white E back onthe road.

By the way, I love Cat down here so it was a great move for me. Only bad thing is no Porsche content at all! They are laid back though, I've had the T sitting in the driveway since Nov. without headlights and never moving with no complaints or issues from the local authorities. I think where I used to live it would have been towed by now a few times!

[MotoSook]

Hey Dennis! Glad to see you post, and I'm very happy CAT worked out for you.

I'll keep a watch for your post/thread when you start digging into the car. Feel free to shoot me an e-mail directly too. I'm not ont he board as much these days.

[wesayso]

I keep comming back to this thread from time to time. Great explaination how to adjust your CIS without all the proper tools available. I've seen a recent thread about the same subject but this one beats it by miles! I never adjusted my mixture going into winter temperatures and the car just didn't feel the same. Today I took the time to do the field adjust and it's running great now. As it should be!

Thanks for this write-up Souk!

[snbush67]

Originally Posted by Souk

I have never heard an idle mixture screw click. What ever book you and your dad are reading, put it down. (There is no one book that I have come across which puts all of CIS's concerns between its cover. So don't assume that book is the end all be all).

"101 Projects for Your 911" MBI publishing, Wayne R. Dempsey 2001

Project 31, Page 95 Tuning and adjusting the CIS Fuel Injection - Maintenance and Adjustment, second Paragraph states: "The screw is indexed so that it should click when you rotate it. Turn it clockwise to richen the mixture, or counterclockwise to lean it out."

Mine doesn't click either, I thought something may have been removed or modified. Were some years screw indexed?

[Johnb911]

My 79 ROW is not endexed either.
It sure would be nice if it was.

[Paulporsche]

I like the fact that mine isn't indexed. It allows for infinite adjustment. Anybody know how many clicks are in one revolution of an indexed system?

[Jim Williams]

Unfortunately, every now and again there will be some bits of misinformation floating around that will get passed on as fact without having been first checked out. The mixture screws for the 911 air flow sensors have never been "indexed" to click as they are adjusted. Anyone adjusting a 911 CIS mixture screw and expecting to hear or feel a "click" will be disappointed.

[William Miller]

I just assumed mine was worn out!
I wonder if the mixture on the MFI screws clicked?

OT:
Jim, have you ever come across part numbers for rebuild kits for Fuel distributers? Someone once told me he had a list, but after pestering the guy for a while, it was never produced. I wonder how they are obtained?

OOT: If you don't already know, I recently came across an area on the BOSCH site "Vehicle Part Finder" that listed their part numbers by application.

[Jim Williams]

Originally Posted by William Miller

I just assumed mine was worn out!
I wonder if the mixture on the MFI screws clicked?

OT:
Jim, have you ever come across part numbers for rebuild kits for Fuel distributers? Someone once told me he had a list, but after pestering the guy for a while, it was never produced. I wonder how they are obtained?

OOT: If you don't already know, I recently came across an area on the BOSCH site "Vehicle Part Finder" that listed their part numbers by application.

Bill,

I expect there are some experts here on the Forum who can answer this with more authority than I, but from my mis-adventures with adjusting the MFI pump some years back, I seem to remember clicks.

Re the fuel distributors, I have found that there are people who say there are rebuild kits available, but when asked for details, are unable to produce them. My findings are that there are authorized Bosch rebuilders who have access to the parts, but to them, this is proprietary info they won't share for fear it will impact their business.

Re the BOSCH part finder, I had a URL once that listed CIS parts, but can't seem to find it now. If you have such a URL, I would appreciate a link.

[William Miller]

I've run into the same thing.
I did find a guy who has a Delorean SP? site that rebuilds several versions of the Bosch fuel distributer

I hope this link works!
There is some other interesting resources there as well.


http://http://www.boschautoparts.com/Resources/VehiclePartFinder/

[jinxy666]

I am reading this with interest but I need to adjust my idle speed as it is quite low ( 600rpm ) and sounds as if it is hunting...just a little, however when I put light pressure on the accelerator and bring it up to about 850'ish it sounds perfect. Can you please tell me how to find my adjustment screw. I have a 1983 911SC.

Thanks for any help.

jinxy

[LM3929]

subscribed great work

[Jim Williams]

The idle adjustment screw is on the front (front is the side towards the front of the car) of the throttle body. It is accessible from the left side. Without actually measuring it, it is about 1/2" in diameter with small "flutes" in the gripping surface so you can turn it by hand, alternatively, it also has a flat blade screwdriver slot. Turning counter-clockwise increases the airflow which increases the idle air bypassing the throttle plate, and increasing the idle speed.