CISe system q's [Answers - long]

[abatzis2 at hotmail.com (Michael Abatzis)]

>From: Jason <jason@scirocco.org>
>
>At 12:58 PM 7/24/2003, Ryan H wrote:
>>Well, if your car was running limp-mode, you'd really notice it, cause 
>>you'd have NO power.  None.
>
>She actually was -- I saw the 10mA reading.
>Whether the car will actually run like shizzynit is going to be a factor of 
>where the mixture is set.  I'll explain in a minute.

nicely explained, jason (the whole email). confusion is the term "limp home 
mode". true limp home mode is when the dpr plug is unplugged--no input from 
the computer, car runs like shit and is purely mechanical.  the 10ma thing 
isn't really limp home mode, it's just the computer default mode.  usually 
the static 10ma is a bad o2 sensor.  having other bad sensors doesn't give 
you this reading.  other than a bad o2 sensor, the 10ma can be bad wiring 
(sensor-->ecu, ecu-->dpr), or a bad ecu.

>Actually, I've seen it read 0 mA with a dead O2 sensor, too.  As O2 sensors 
>age, they put less and less voltage out, which causes the computer to think 
>the car is becoming increasingly lean.  It'll compensate for it by 
>richening the mixture (reducing the DPR current, eventually to 0).  At some 
>point, the sensor will be totally dead, and then the computer will go into 
>limp-home mode.  (More below).

makes sense, but i've never seen it.

>It actually works all the time -- not just the first 30 seconds.  It's a 
>potentiometer that measures rate of change of the airflow meter.  It will 
>respond by richening the mixture under any quick throttle transitions.  
>Unplug it, and you'll feel no big difference under steady-state cruising.  
>But any time you make a sudden downward movement of that pedal, the engine 
>will bog for a second until the mixture catches up.  There are a lot of 
>reasons why you want a richer mixture under transitional throttle, but one 
>of the big reasons this device is used is to compensate for the time it 
>takes for the air flow plate to move and to actually supply extra fuel to 
>the injectors when the throttle is suddenly opened.
>

interesting. when i was troubleshooting my slow car (still no solution, btw) 
i noticed the values for the potentiometer were off. i thought this was only 
cold running mode also, so didn't bother to change it...




>If you watch what happens to the DPR after you start the car, you can see 
>that it gets a high current from the computer, richening up the mixture at 
>first.  This value then drops to the "baseline" value, which is usually 
>around 10mA.

this is because the ecu isn't initially getting input from the o2 sensor, 
because the sensor hasn't warmed up yet and started working.

-Michael Abatzis
New Orleans!
1988 Scirocco 2L 16v RIP-->parting, finally taking orders: 
www.learnlink.emory.edu/~mabatzi/mikes_page1.html
1987 Scirocco 2L 16v...

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