CIS theory ?

[Ameer Antar]

ok here goes...

1. open loop occurs when the engine is cold, unless your O2 sensor is 
heated [3-wire], and when the WOT switch closes. At WOT the ECU puts out a 
fixed, pre-determined duty cycle, about 85% I think, but it should be in 
Bentley. The ECU ignores the O2 sensor input, and keeps it at 85%, giving a 
rich mixture for maximum power. I don't know if the ecu is open or closed 
loop when the idle switch is closed, though.

2. Other than engine temp switches and throttle switches the ecu mainly 
relies on the o2 sensor for FV duty cycle.

3. I'm not sure what you mean exactly, but the WOT switch just tells the 
ECU to change the FV duty cyle to a fixed value, ignoring the input from 
the o2 sensor.

The o2 sensor provides output to the ecu, telling it where the mixture is. 
The ecu then sends a duty cycle signal out to the Freq. Valve which adjusts 
the mixture, by changing the fuel pressure on top of the fuel distributer. 
This fuel pressure provides resistance against the air-flow plate, and 
changing the pressure changes how much the plate deflects for a given flow. 
They say the ECU is like having a mechanic under the hood while you drive, 
adjusting the mixture for all possible conditions. Think of the O2 sensor 
as the mechanic's test probe or voltmeter, and the frequency valve is like 
a mixture adjustment knob.

Seriously, the Bosch book by Charles Probst will help you out a lot. It's 
only $22 and it covers CIS and Bosch hot-wire as well. good luck.

-ameer


At 02:51 PM 10/30/00, you wrote:
>I am learning how it works on Audi200tq 89. It has K-Jetronic with O2
>control. I have some questions about it:
>
>1. What triggers transition from open loop to closed loop?
>
>2. Are there any other signals (from sensors and/or switches), except
>from O2 sensor, that  ECU uses to set frequency valve duty cycle?
>
>3. Does WOT condition affects FV duty cycle via anything else but O2
>sensor?
>
>I will appreciate your help.
>
>Konstantin Bogach.