# Tuning CIS Using a O2 Sensor



## 79MK1Scirocco (Aug 23, 2011)

Has anyone built their own Gas analyzer using an O2 Sensor? 
I have been looking at some sites that recommend using a heated O2 sensor 
Someone once told me that you can use the Single wire O2 sensor and a multimeter. 

http://jimsprojectgarage.weebly.com/edelbrock-carb-tuning-with-a-narrowband-oxygen-sensor.html
(towards the bottom of the page is the build)

https://www.summitracing.com/parts/edl-6593/overview/


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## Butcher (Jan 31, 2001)

Here's my 2 cents worth. Jim is very misleading and therefore his information is not exactly correct.

Think of an O2 sensor like this. It will only show you that it is running rich or lean. That is it. Rich or Lean. The computer will take that signal and when it runs rich, it leans the mixture, when it runs lean, it enriches the mixture. If there is a good amount of cycles, crossover is hit more often and therefore it runs pretty good.

Today's wide band sensors will show you where your mixture is at all times. It will show if you're at 13.7, 14.2, 15.7 etc. If you are tuning, that is the sensor you need. Those systems are a bit more and the sensors are pretty sensitive.

Do not believe me? Take a look at this site http://www.enginebasics.com/EFI Tuning/AF Ratio Basics.html That site says the O2 sensor will read stoichiometric but I beg to differ. I've done enough diagnosis and the sensor only stays at .45v when the Injection ECU is biasing it to that voltage.

So, I really do not believe you could tune any fuel system with a narrow band O2 sensor. Wide band is the best/easiest way.


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## 79MK1Scirocco (Aug 23, 2011)

Thanks for the 2 cents,
Do you have a set up that you use to tune the mixture or do you just take it to a shop?
Honestly I have not had much luck taking this car to any shop.


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## Butcher (Jan 31, 2001)

The only time I ever needed any kind of tuning was when I ran DCOE Weber's and they did not have O2 sensors back in the day. I certainly needed one. There was a lot of guessing, checking plug colors, and overall and art. Someday when I restart my Callaway turbo project, I will use one.

Years ago I did purchase a LM1 [http://www.innovatemotorsports.com/press/pr-lm1.php] and it is still new in the box. The biggest issue with a wide band is that you need a hole for an O2 sensor. The other issue you may have is the patience/skills to work with an old CIS system.


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## vwjunkie747 (May 22, 2013)

This is how you want to adjust A/F ratio
http://mikegabriel.ca/vw/badhabitrabbit/adjusting.html


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## Butcher (Jan 31, 2001)

That website is a bit misleading.

If the needle is moving, the mixture is correct, where ever it is on the scale [unless it's pegged]. What you are trying to do is make the adjustment so the 'correction' is in the middle. The only time it may run rich/lean is when the O2 sensor is off/unplugged but in a properly running system, that only should last a few minutes.

One trick to determine if the fuel distributor is good is to check/adjust the idle mixture to 50%. Rev it to 3k and see what it's doing there. It should be within 10% of the idle reading. This is assuming you have no intake leaks.


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## Jon85 (Aug 17, 2012)

so i have a 1985 golf custom, and speaking with joey from doubleJs in Portland OR. with a dwell meter or a multimeter set to hz/%, using the % you should have the setting at 43% +/- 7% with the engine set up for base idle set, you know, disconnect that, pinch this.....i have done this and it runs a lot better then it did, but i still had the misfire issue. i corrected that with the blue wire performance kit, German made distributor cap and rotor from techtonics tuning in Sheridan OR.

The car runs like it has a whole new lease on life, and i have already seen an increase with fuel economy, and overall performance!!


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## 79MK1Scirocco (Aug 23, 2011)

Thanks for everyones input on this.
Unfortunately those links all have a test port that my CIS dies not have with the narrowband O2 sensor.
So after some research I decided to put in a wideband and tune from there.
http://www.wide-band.com/product-p/apsx_d2n.htm

I recently purchased an Abarth exhaust system from another member on this site. I decided to put that it in since I was going to have the welder and exhaust out to weld on the bung for the Wideband

Flex Pipe with O2







[/url]20180803_184413 by Chris Carpenter, on Flickr[/IMG]








[/url]Scirocco by Chris Carpenter, on Flickr[/IMG]

Abarth 







[/url]Scirocco by Chris Carpenter, on Flickr[/IMG]

Old exhaust- fun fact; my uncle lost his job over this back in the day when this was my mom's car







[/url]Scirocco by Chris Carpenter, on Flickr[/IMG]


So far I have been able to get the light cruising and idle reading to hover around 14-15
Load and acceleration readings have been around 11- 9.8
more road testing and pics to come...


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## Butcher (Jan 31, 2001)

Great. Now all you need to do is play with it. You will see proof positive the 'tricks' you do and the results of those tricks.


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## 79MK1Scirocco (Aug 23, 2011)

After some playing around i still can't get that rich mixture to come down. 
I i suspect that I have a vacuum leak some where. 

Sent from my SM-G930V using Tapatalk


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## Butcher (Jan 31, 2001)

A vacuum leak would give you a lean mixture. The additional air that a leak will cause does not get metered and therefore that is why less fuel would be delivered.


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## 79MK1Scirocco (Aug 23, 2011)

What do you think might be causing a lean idle and rich Wot?
A friend suggested disconnecting the vac line to the WUR. 
The car ran rich all around when I did. 
I was able to get idle in the high 14 -15 range and crusing 13-14 range with the 13mm screw.
Under boost it will not drop below 9.8 now.
I am hoping to tweak the WUR and idle screw at the airflow meter together to get idle and boost afrs right. 
Any thoughts?

Sent from my SM-G930V using Tapatalk


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## Butcher (Jan 31, 2001)

CIS is hard to change what you are trying to do. I promise it is difficult for me to explain what I'm thinking, but I will try.

If you change the fuel pressures, it will effect the entire spectrum [from idle to full throttle]. So if you lower the control pressure, it will enrichen the fuel mixture everywhere. If you raise the system pressure [which I have not done before] I suspect, it will do the same.

You can change the fuel mixture at idle thru the 3mm screw. You are actually changing the entire mixture but there is more of an effect at idle than it is at full load. So right now, to get your idle mixture richer, adjust the 3mm screw to get to where you want to be. It will enrichen the upper spectrum but not at the same percentages.

The air flow housing is where the plate runs in and that has different tapers for different air flow. There are different housings that will allow for different requirements that the engine needs. You could check other housings to see if there is a housing that is wider at the top [which would allow more air to go around the plate allowing or a leaner fuel mixture]. You certainly could modify the housing at the upper portions by porting it. You certainly would be on your own since I do not think people go to those extremes with CIS. I certainly would not modify a housing that I did not have a spare laying around. There was a time year ago that someone made a sleeve that fit the top of the housing that made the top portion smaller. It allowed for a richer mixture. That was way before the internet was around. I understand, you want to go leaner at the top range. 

Again, I'm sorry that my explanation is not very good but I hope you get what I'm saying.


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## 79MK1Scirocco (Aug 23, 2011)

Butcher said:


> CIS is hard to change what you are trying to do. I promise it is difficult for me to explain what I'm thinking, but I will try.
> 
> If you change the fuel pressures, it will effect the entire spectrum [from idle to full throttle]. So if you lower the control pressure, it will enrichen the fuel mixture everywhere. If you raise the system pressure [which I have not done before] I suspect, it will do the same.
> 
> ...


This makes a lot of sense.
If I understand what you are saying about the air meter it comes down to the fact that I need to flow more air into the engine. the stock unit is too restrictive as is.
I do have a Volvo air metering unit that does have a larger air plate.
I should probably upgrade the air box too.


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## Butcher (Jan 31, 2001)

The air flow meter measures the air and will lift the plunger to allow the right fuel mixture at every point of the travel. 

What you want to do is to allow the air flow meter to send a different movement so the fuel is delivered at a different rate. If you in decrease the shape of the cone, the air will move the plate more. More movement = more fuel. If you enlarge the shape of the cone, more air will bypass the plate and therefore the plate will not move as much which = less fuel.

When it leaves the factory set up properly, the fuel mixture will be delivered at the right rate per air flow.


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## 79MK1Scirocco (Aug 23, 2011)

So I had the bottom port of my boost sensitive WUR vented to the atmosphere.
This seems to be a common thing to do. 
My friend suggested that I connect it and see what happens. So I did with a check valve in place. 
Sure enough now the afr has not droped below 11 under boost









Sent from my SM-G930V using Tapatalk


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## DbilasTDI (Nov 5, 2017)

All you can set is the base mixture. Connect a digital meter to the O2 sensor output, adjust 3mm for .75-.80 VDC - blip the throttle each time you make a change, let it settle back to steady idle before re-checking.

A colortune might be easier on a 79 Scirocco.

On those early cars I always do it by ear, go SLOWLY richer to the best quality idle.

If you have a cam in it forget the meters and just do it by ear, the numbers won't matter because it will not be happy unless it is rich. They want to run fat with a cam.

I still love CIS basic.


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