CIS Idle Speed and Mixture Setting Without an Analyzer

[emac]

Ok
Has anyone heard or tried to adjust with a digital VOM?

[Walter_Middie]

emac,

Are you thinking about a dwell meter? Those of us with points still use this outdated tool. If you do a search, you will find lots of info. I copied this off of Pelican a few years ago:

There is a test connector behind the plastic cover on the left side of the engine compartment. If you hook up an analog dwell meter to the pin with the green and white wire, you can see the FV duty cycle. The system is open loop when cold and the meter should show a steady 58 (65% duty). Once the engine is above 15C, the needle should start fluctuating between 40-58 in a steady rhythm. If the needle doesn't fluctuate you need to test the 02 sensor. If the needle fluctuates between 20-30, the mixture setting is too rich, between 60-70, too lean. When you set the mixture on this system, you are really only altering the open loop mixture (cold and WOT), the system corrects the mixture back within the range. I usually set it around 30-40, because I have found the WOT mixture too lean on many of these engines.

[emac]

Rex

No I think I lost my last dwell meter about thirty years ago. Someone had posted something some months ago about using a DVM. I do remember something about hooking up to the oxy wire and ground but forgot where to set the meter. Anyway thanks for the info and time.

[Gunter]

jinxy:
Like Jim says.
You also mention some hunting.
Idle speed and mixture are ajusted in conjunction.
To set the mixture, you'll need a LONG 3 mm Allen key.
Look for a small hole between the fuel distributor and the air sensor plate housing.
Set the approximate idle speed like Jim says, then insert the Allen key and fish for the small hex set-screw.
Turn very small amounts: Clockwise a little until the idle gets rough, then counter-clockwise until it gets rough again, then set it in the middle of the range.
Do not rev when the Allen key is in the set-screw.
It takes a little practice; do a search here on: "Mixture adjustment"; lots of info.
Of course, the shops use an exhaust gas analyzer to set the mixture instead of setting it by ear.
Your '83 may have a lead plug in the small hole. In that case you cannot adjust the mixture until the plug is drilled out.

I recommend that you get the Bentley SC Repair Manual.

[jinxy666]

Yep, found it and done the adjustment.It is idling at around 850rpm......sounds much better.

Thanks for that jim cheers.

jinxy.

[Johnb911]

Found this link in another post.

Go to downloads and click on the bosch cis link

Great read on the CIS SYSTEM




http://www.phat-gti.com

[MPDano]

Originally Posted by Gunter

jinxy:
Like Jim says.
You also mention some hunting.
Idle speed and mixture are ajusted in conjunction.
To set the mixture, you'll need a LONG 3 mm Allen key.
Look for a small hole between the fuel distributor and the air sensor plate housing.
Set the approximate idle speed like Jim says, then insert the Allen key and fish for the small hex set-screw.
Turn very small amounts: Clockwise a little until the idle gets rough, then counter-clockwise until it gets rough again, then set it in the middle of the range.
Do not rev when the Allen key is in the set-screw.
It takes a little practice; do a search here on: "Mixture adjustment"; lots of info.
Of course, the shops use an exhaust gas analyzer to set the mixture instead of setting it by ear.
Your '83 may have a lead plug in the small hole. In that case you cannot adjust the mixture until the plug is drilled out.

I recommend that you get the Bentley SC Repair Manual.

This is a great write up. Ok, if I understand correctly. Set my idle (4.5 Auto) at around 850. Richen - clockwise till rough then lean till rough while making note of how many turns. Then adjust clockwise 1/2 those amount of turns. Does this sound correct? Also, I did look in my WSM and my engine timing should be set to 31 degrees. My Harmonic Balancer shows 28 degrees, I set to a little higher than the mark. Am I in the ballpark?

[Gunter]

You've got the general idea.
The whole movement is not even a full turn; a little cw, then ccw, then set it in the middle favouring slightly rich.

This is for Bosch K-Jetronic CIS in general terms; the optimum way is still with an exhaust analizer.

The ignition timing has to be done according to what the manufacturer calls for.
Like vacuum disconnected, RPM, Degree BTDC etc.
If the distributor hasn't been serviced for many years, consider doing it to make sure that it has the right curve.

[MPDano]

My fellow 928 buddy and I went though the procedures on doing the ignition timing and then did the a/f adjusting. My rear brakes were apart while we did this, so we couldn't test drive. Sounds more responsive when blipping though. Thanks for the suggestions and I will let you all know of the outcome.

[prebordao]

Sorry to ressurect this thread, but I'm trying to adjust the mix without a CO analyser...

However, I have trouble adjusting it with the car running. Whenever I touch the hex screw with the key, as carefully as I can, the engine splutters and dies...

Might indicate that he's close to one of the extremes (too low / too rich) ??

[MotoSook]

If I had to guess, it is running very lean. Downward pressure on the screw results in downward pressure on the air meter lever arm which also allows the fuel plunger to slide down in the fuel distributor.

If there is nothing else wrong with the car, you can turn the screw while the engine is off. Turn the idle screw 1/4 turn CW and it should richer it up a bit.

But! First ask yourself why you are so lean? The idle screw didn't move by itself so what went wrong to cause the mixture to change? Fix problems...don't compensate for them.

[prebordao]

I was just wondering about turning it with the car running. With the engine off, I can adjust it and feel the results immediately.

Actually, I'm going through the mix after a series of prior fixes:
I had a blockage in the return line, after removing it, I had to re-adjust pressures as they were wrong to compensate for that. Now, that he pressures are right, I'm adjusting the mix.

Believe me, I already spent a lot of hours with CIS, if you cut corners, it will bite you.

[boyt911sc]

Originally Posted by MotoSook

If I had to guess, it is running very lean. Downward pressure on the screw results in downward pressure on the air meter lever arm which also allows the fuel plunger to slide down in the fuel distributor.

If there is nothing else wrong with the car, you can turn the screw while the engine is off. Turn the idle screw 1/4 turn CW and it should richer it up a bit.

But! First ask yourself why you are so lean? The idle screw didn't move by itself so what went wrong to cause the mixture to change? Fix problems...don't compensate for them.

Motosook,

I'm one of the many people who learned from your technique. I'm not sure if you added the above comment in your earlier posts because people tend to jump and tinker the mixture screw without realizing why the mixture changed in the first place. This mixture screw would not change its setting even if you wrecked the car!!!! Thanks.

Tony

[MotoSook]

Unfortunately, I cannot edit the firsdt post...the older posts are locked for what ever reason.

So hopefully folks will ready further than the first post.

[_cy_]

good info

[gtrp]

This just saved my 911sc. Bump as many people should be reminded of this thread after I spent days looking thru threads that just said "search"

[Jay Laifman]

There are two conflicting statements above. Anyone know which one is true?

(1) When you stamp on the gas, if you get a split second of hesitation before the car picks up, is this an indication of too rich.

(2) If you get a little hesitation when accelerating from a stop, like the engine is kind of "spooling up" before it pulls strongly, then the mixture is probably too lean.

[Bob Kontak]

Originally Posted by Jay Laifman

There are two conflicting statements above. Anyone know which one is true?

I don't see a conflict. Split second and spooling up are two different things.

I am not saying either is right as I do not know.

[Jay Laifman]

Ok. Well, either way, my car isn't doing either!

I just didn't see the difference. Per another thread, I've got a 73.5 CIS 911 where I have the 75 911 WUR. I never had the vacuum line hooked up. But I'm going to do it shortly. This means my richness will need to be adjusted. So, I'm just reading up in anticipation of having to get it right again.

[Jay Laifman]

Actually, I have another question I don't see answered above. What is the usual range of adjustment between the two ends? I mean it says above to turn it CW until rough and CCW until cough, then set in the middle. So between the roughness and the cough, are we talking about 1/2 a turn, a full turn, more, less?

Thanks.