Vladimir
15+ Year Contributor
- 279
- 36
- Apr 28, 2010
-
Winthrop harbor,
Illinois
Tried to look for a similar thread but didn't really find what I need. Was looking at the diagrams on a 1990 1g. ISC has 6 wires 2 power and ,4 grounds controlled by ECU . There isn't however any reference wires that give feedback back to the ECU. What is the theory of operation?
Im assuming that instead of a regular DC motor, ISC is more like a stepper motor. Where the ECU cycles the ground a whole bunch of times to get it's preferred position Based on the inputs from MAF, TPS and ECT - ECU blindly adjust the position of the valve based on a factory programed sequence?
Or is it more like a servo motor? Where the ECU controls still have the same inputs but the ECU knows the exact location of the valve based on internal resistance of each pin, or maybe it breaks the ground and stops cycling the motor, once the draw value changes? This would notify the ECU the exact location of the valve. To me this is less likely for early 90s, but I'm not deep into circuitry and controls. Because the metered airflow shouldn't really change with the air bypassing throttle body, it's still gonna read the same value. Im assuming it would use MAF to verify ISC position. And I don't think that in closed loop the computer would read AF ratio to check IAC position
Reason why I'm asking is because the ISC can have 30 ohms of resistance on every position. But that wouldn't verify that it can freely move, or the plastic valve isn't broken/binding around the threads on the rod that controls it.
If I provide the 12v and ground to one of the position pins, Would it just click and not rotate like a regular DC motor? Would i have to know the sequence on how the ECU cycles the ground to extend it or retract it? Or once I give it 12v and ground off one of the position pins it would just freely move to a desired position till it bottoms out or something?
How would I know if the ECU is bad going crazy cycling the ISC or the ISC is just binding and never reaches it's desired position? Would the computer just cycle the valve non-stop if it got stuck, or would it fire a pre programed sequence and assume that the valve is doing it's job, until it sees that the airflow is all out of wack?
Who knows the whole theory of operation? I would be interested to find out.
Im assuming that instead of a regular DC motor, ISC is more like a stepper motor. Where the ECU cycles the ground a whole bunch of times to get it's preferred position Based on the inputs from MAF, TPS and ECT - ECU blindly adjust the position of the valve based on a factory programed sequence?
Or is it more like a servo motor? Where the ECU controls still have the same inputs but the ECU knows the exact location of the valve based on internal resistance of each pin, or maybe it breaks the ground and stops cycling the motor, once the draw value changes? This would notify the ECU the exact location of the valve. To me this is less likely for early 90s, but I'm not deep into circuitry and controls. Because the metered airflow shouldn't really change with the air bypassing throttle body, it's still gonna read the same value. Im assuming it would use MAF to verify ISC position. And I don't think that in closed loop the computer would read AF ratio to check IAC position
Reason why I'm asking is because the ISC can have 30 ohms of resistance on every position. But that wouldn't verify that it can freely move, or the plastic valve isn't broken/binding around the threads on the rod that controls it.
If I provide the 12v and ground to one of the position pins, Would it just click and not rotate like a regular DC motor? Would i have to know the sequence on how the ECU cycles the ground to extend it or retract it? Or once I give it 12v and ground off one of the position pins it would just freely move to a desired position till it bottoms out or something?
How would I know if the ECU is bad going crazy cycling the ISC or the ISC is just binding and never reaches it's desired position? Would the computer just cycle the valve non-stop if it got stuck, or would it fire a pre programed sequence and assume that the valve is doing it's job, until it sees that the airflow is all out of wack?
Who knows the whole theory of operation? I would be interested to find out.
