How do I set the mixture properly on my 911 CIS (non lambda)motor?

[MBEngineering]

HI Daviboy
I have no scanner, so I have tried again for you ;



do not forget to disconnect the air pump before adjusting the CO%

regards mike

PS if you are having prob's reading it now !!!! PM me you snail mail Add and I will send you over my glasses to read it??

[Daviboy]

Thanks MB thats better. Oh and I dont have an air pump BTW. And I have MY glasses on now it helps

[Wyvern]

I know I picked up an old thread ...

But is the asumption that is the Idle mixture is correct that the mid and WOT mixture falls into place ???

[snbush67]

Originally Posted by Wyvern

I know I oicked up an old thread ...

But is the asumption that is the Idle mixture is correct that the mid and WOT mixture falls into place ???

Yes, as long as everything else is working as designed.

[boyt911sc]

Originally Posted by Wyvern

I know I oicked up an old thread ...

But is the asumption that is the Idle mixture is correct that the mid and WOT mixture falls into place ???

Wyvern,

Here is a section from the Bosch technical bulletin K-Jetronic about load conditions:

"The adaption, or correction, air fuel mixture to the operating conditions of idle, part load and full load is carried out by means of appropriately shaping the air funnel in the air-flow sensor.

Hence, the funnel is so shaped that a richer mixture is produced at idle and full load, and a leaner mixture at part load (full-load and idle enrichment)".

End of quote.

Tony

[Wyvern]

Thanks for answering my question .

Really is back-wards of all other carb and FI jetting I have done .

but to fine tune (and if try to error on the rich side for WOT) my idle setting may need to be on the extreme of (or actually a bit past that) of specified idle setting ?

I am thinking out loud here ...this is complicated a bit by the fact that the idle screw is a controlled leak and not an enrichment circuit.
So a idle screw that is "off a bit" at idle can be compensated by the mixture screw being also off a bit...eg: rich on mixture and lean on idle cold read correct on O2 and vice versa.

My issue is that I am Rich at Idle and Lean on WOT.
..again thinking out loud ...
I may screw the Idle screw out a bit (that would lean it out) and my Mixture screw a bit richer.
OR ... if I lower my warm control pressure that wouldd allow a richer curve to WOT ... ?

A very fine balance indeed.

[Jim Williams]

Originally Posted by Wyvern

Thanks for answering my question .

Really is back-wards of all other carb and FI jetting I have done .

but to fine tune (and if try to error on the rich side for WOT) my idle setting may need to be on the extreme of (or actually a bit past that) of specified idle setting ?

I am thinking out loud here ...this is complicated a bit by the fact that the idle screw is a controlled leak and not an enrichment circuit.
So a idle screw that is "off a bit" at idle can be compensated by the mixture screw being also off a bit...eg: rich on mixture and lean on idle cold read correct on O2 and vice versa.

My issue is that I am Rich at Idle and Lean on WOT.
..again thinking out loud ...
I may screw the Idle screw out a bit (that would lean it out) and my Mixture screw a bit richer.
OR ... if I lower my warm control pressure that wouldd allow a richer curve to WOT ... ?

A very fine balance indeed.

Just to be clear on the functions of the Idle screw and the Mixture Screw: The idle screw (on the throttle body) only affects the idle RPM. The CIS looks at the idle screw the same as opening or closing the throttle plate. The mixture screw (on the Fuel Distributor) affects the air/fuel ratio. The mixture screw may indirectly affect RPM.

Also the term "leak" as applied to CIS is usually looked on as referring to unintended outside air (unmetered by the airflow sensor) entering the air/fuel mixture. The idle screw should be looked at as "bypassed" air (around the throttle plate).

For some basic CIS info, look at the CIS Primer on my Rennlist site:
http://members.rennlist.com/jimwms

or JimsBasementWorkshop at:
http://jimsbasementworkshop.com

[boyt911sc]

Originally Posted by Wyvern

Thanks for answering my question .

Really is back-wards of all other carb and FI jetting I have done .

but to fine tune (and if try to error on the rich side for WOT) my idle setting may need to be on the extreme of (or actually a bit past that) of specified idle setting ?

I am thinking out loud here ...this is complicated a bit by the fact that the idle screw is a controlled leak and not an enrichment circuit.
So a idle screw that is "off a bit" at idle can be compensated by the mixture screw being also off a bit...eg: rich on mixture and lean on idle cold read correct on O2 and vice versa.

My issue is that I am Rich at Idle and Lean on WOT.
..again thinking out loud ...
I may screw the Idle screw out a bit (that would lean it out) and my Mixture screw a bit richer.
OR ... if I lower my warm control pressure that wouldd allow a richer curve to WOT ... ?

A very fine balance indeed.

Wyvern,

We had numerous PM's between us and your approach to CIS is not same as with carburated engines. Idle throttle screw and mixture screw are two completely different components of the CIS system. Take time and browse Mr. Williams website, the information you will gather is priceless.

You are an experience mechanic (?) but have limited exposure to CIS. So getting to know the details for CIS troubleshooting should not be a problem for you as long as you familiarize yourself to the system.

Given enough time and exposure to CIS, you'll be a good troubleshooter. Keep active and participate in CIS troubleshooting threads so it will enhance your perspective on this subject.

Tony

[Wyvern]

Thanks guys ... appreciate your knowledge.

I DO need to remember that this is CIS and not carb or the FI system that I am used to.

Also the terminology ... I'll get it

I came to my last thought pattern because I did have my vehicle on a CO meter.

The pressures are set but still in my terminology rich at idle and lean at WOT.

The CO meter is stationary so not able to take it for a "ride"
I guess thats OK if the system really is set at Idle.
BUT it did change readings while using the Idle screw ????

...also sorry to hijack your thread