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

Guys,
I know I am going to take a lot of flak here so am hunkering down for the barrage. I have an 82 SC without lambda sensor as I have headers and no O2 sensor. Everywhere I read (here and Rennlist forum) all the advice for setting the mixture on the motor is for cars with lambda.
I think I basically understand the CIS system however how do I set mixture after an air-box replacement?

Best is to make sure your fuel pressure is good, get the long hex key and use a smog box for the tail pipe.

i set mine by making small CW changes until it surged at idle, then turned it CCW about half a turn then CW to the last place it did not surge. drove it and if the RPM's dipped down when i let off the gas, then i would do the CCW then CW and make it just a Little leaner until the RPM's dont dip. i had it checked later and it was dead on 3%. basically, set it as rich as you can without idling problems.

find a shop with an exhaust analyzer and set it to 3-3.5%.

Thats it stick an O2 sensor in the tail pipe and adjust idle mixture till 3-3.5% reading achieved?

Yep thats it...I took John Walker's advice on this many years ago. Back then he also recommended a timing setting of 5 degrees BTDC. JW is one of the real guru's on the board, we are all glad to have him as a resource, IMHO.

Also know that as you adjust the CIS mixture you will change the idle RPM. Changing the timing will alter the idle as well. So, I set my timing first, then adjust the CIS keeping the idle around 1000 RPMs. After getting the A/F the way you want it, dial down the idle to 950 or so... At least that the technique that works for me.

Kemo,
Thanks just cannot believe it is that easy, this I will attack on my own no problemo. Excuse my ignorance but what does BTDC mean....doh my guess is Before Top Dead Center, am I correct am I am I? If so how is that done??? Sorry

Correct on the BTDC. To set it you need a timing light and adjust your distributor by loosen the mounting nut and rotate it slightly to set it at 5 deg, btdc at 950 -1000 rpm.

Even though you don't have a sensor, the rest is still Lambda unless you removed other components?

Set the mixture as advised by others; it takes a few tries between mixture screw and the fast-idle screw.

Set the timing at 5 deg BTDC with vacuum disconnected at ~950 RPM.

If its still has the lambda gear and no O2 sensor you need to get it sorted. If you search under my name you will see two dyno runs, one with the O2 sensor hooked up and the mix set per the factory. The second is disconnected and set to 3.5%, the 3.5% run is a mess, AFR's are all over the place and power is down.

With the sensor connected and all of the equipment working the AFR's are near perfect and the power is much better. The default operating mode of the frequency valve appears to cause this.

Gunter,

Could you be more specific about what other component/s needed to be removed? And why? Thanks.

Tony

Even though you don't have a sensor, the rest is still Lambda unless you removed other components?

Gunter mine is a euro ROW model therefore no lambda equipment or sensor. I would appreciate a post with pics of setting timing if possible!

On a 1980-83 US 3.0 with Lambda, a lot of people use the CIS from 1978-79; it has larger intake runners and no Lambda.
No brain, no Frequency Valve but still has AAR, AAV, Decel.Valve, TTS, CSV.

I dont have any pics...but a good thing to do would be to find the markings for setting the timing and make sure you can clearly see them before you hook up the timing light.

just to the right of the Z1 mark, you should see another tickmark, possibly with a 5. This is the 5 Deg mark and thats what you line up to the tick mark just above the wheel when you spin the distributor to adjust the timing. Some timing lights allow you to preset the light with a certain advance or retard. If you are using the 5 mark to line up, make sure your timing light isn't set up for advance.

I think now would be a good time to suggest Waynes 101 Projects book. It has great pictures for doing this. I also think some good pictures could be found searching the threads for valve adjustment, as you need to use the markings for this procedure to get the #1 cyl to TDC.

Kemo,
Thanks I have Waynes book coming in a shipment along with a new airbox + gaskets and ruubers, front rotors and pads + caliper rebuild kit, clutch cable, pedal bushing kit, headlight relay kit, factory short shift kit + new bushings, valve cover gaskets, oil filter + seals, and some other goodies. So I will be leafing through his book quite extensively in the weeks to come. I am sure the wife will be charmed but what the hell it keeps me out of trouble.... well other sorts of trouble lol.

nice...i agree.

let us know how things turn out with the projects and good luck.

Sorry if I'm intruding here...

What if you want to adjust the mixture without the cat installed? (I have a pre-muffler installed instead)

What will the correct O2 sensor reading be then?

Otto

HI Daviboy
If you a 81/82 engine then you need to look at this chart, if it is NOT US spec, as the CO% will be to high at 3% and the engine will hunt at idle;

http://forums.pelicanparts.com/uploa...1222789863.jpg

has your engine a air pump on the L/H side of the engine ne'er the dist, if so remove the belt before adjusting the CO%, and always adjust the CO% from weak to rich as the small relay arm in the air flow sensor plate will be tight and some times sticks.

regards mike

Oh and if you buy the pelican "T" allenhead tool for adjusting the mixture you'll probably have to cut down a bit--too high for my 79, anyway. Or find another allenhead.

Good luck and have fun with Wayne's book--should pick up a Bentley, too. Between the Board, Bentley, and 101 you ought to be able to figure anything out.

Mike,
My car is non US it a ZZZ ROW car. Is there any way you can scan and send me that chart, it is ompossible to read from the picture? If so send to davy_1010@yahoo.com

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

http://forums.pelicanparts.com/uploa...1222962198.jpg

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?? ;)

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

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 ???

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

Mixture adaptations.......
 

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

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

Follow the guru's advise.........
 

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

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