CIS tuning

[DeWitt Harrison]

On Thu, 21 Jan 2016 15:40:36 -0800 radek at uniserve.com wrote:
<radek at uniserve.com>

> Hello all surviving CIS fans :)
>
> I decided to finally tackle the high idle problem in my winter ride,
> an 88 90Q.  I borrowed a wide-band O2 gauge, showing actual
> air-to-fuel ratio.  For now, I just removed the existing O2 sensor,
> replaced with the gauge's sensor and fired up the car.  First, it was
> running very rich, until it warmed up.  Once warm, the mix would be
> around 14:1 at idle, but would get very lean at higher rpms, up to 17:1.
>
> Are these results meaningful at all, without O2 sensor connected?
>
> The gauge has an output wire that can simulate O2 output to the ECU,
> which can be set (in low-voltage mode) to between 0 - 1 V.  According
> to Huw's page, this is the range a regular O2 sensor operates on?
> Just want to double check, wouldn't want to fry my ECU.
> Thanks for any input and guidance,
>
> Radek.

Provided all the CIS sensors, such as the stock, narrow band O2 sensor,
temperature sensors, and the essential idle control items such as the idle
control air valve, air flow meter adjusting screw, etc., are working, just
follow the factory procedure (Bentley) to properly set the idle control air
valve duty cycle. To do this easily, you will need a couple of DVMs and a
made up test cable to put in series with the ICV. (Gross air leaks from
cracked hoses would have to be addressed beforehand as well.) Other than
that, there is not a whole lot to be done to adjust AFR at other operating
conditions although some CIS tuners have messed with trick control
pressures and other weird stuff (Hello Scott J.!) to get richer AFR at WOT.

DeWitt Harrison
1988 5ktq