CEL possible O2 sensor 1.6 bar now 1.3

[Edward R. Wendell IV]

> Lister(s): 200 20V 3B
>
> I'm prepping for a track event and seem to be slipping backwards.
>
> We chased down some vacuum leaks and the car ran to 1.6 bar (93) 
> octane.
> Now the car has hesitation and when it does, it only pulls 1.2 / 3
> bar.........where I started before chasing vacuum leaks.............
>
> Now the ChkEngLight has come on. and its on quite a bit now. (Today)
> Vag-Com car tonight  DTC is :
> 00537 - Lambda Oxy sensor regulation 08-00 control limit surpassed.
> Now I just put this new $130 full cord & plug one (I wanted it) in 
> last Aug.
> ~7,000 miles ago.  (Car sat all winter)
>
> Using the measuring blocks on Vag-Com Field 8 is a value which the 
> book Vol 1
> pg 24-90-2 says: "MUST fluctuate around an average of 128.  Value is 
> 160.
>
> So I'm leaning towards the O2 sensor bad............
>

Disclaimer: I have no personal experience with the 3b, but I do have 
experience with other Motronic systems and it's variants.

I think that you have to get away from the idea that a component fails 
and the computer tells you which component it is. I've had lots of 
experience with "self diagnostic" systems on everything from supersonic 
jet bombers to my various cars and they all have the fundamental flaw 
that they are only as good as the person that wrote the code and the 
guy that designed the physical system. In this case I highly doubt that 
your o2 sensor is bad again already. In my experience they are very 
reliable pieces unless you've been running leaded avgas or have some 
major engine problem that is causing burnt oil or antifreeze to exit 
the engine via the exhaust. I would instead start looking at other 
factors that would cause the mixture to go either too lean or too rich 
to the point that the closed loop system can't compensate. That's what 
the code is really telling you, that the sensor is detecting a lean or 
rich condition, is trying to compensate for it, and can't (notice the 
"control limit surpassed" part of the error description). The closed 
loop o2 system only has so much say in the air/fuel ratio equation that 
the ecu is running, say .5. If something else such as the airflow meter 
or incorrect fuel pressure throws off the mixture by more than that you 
will get the exact code you are seeing. As a matter of fact, all the 
vehicles that I've worked on so far run quite well with the o2 sensor 
disconnected. A closed loop o2 sensor system is something of an add on 
feature to the basic airflow or load based stored  fuel map. Because a 
standard narrow band o2 sensor is only accurate at indicating rich or 
lean, most systems cycle between rich/lean a few times a second in 
order to reach an average of 14.7. The fact that your reading is stuck 
at one value that is well out of range says that the afr is way outside 
the range for which the o2 sensor and ecu can compensate for when the 
conditions are met for closed loop mode.

Roy Wendell
Clarksburg WV USA
86, 87 5kcstq
87 MR2 times 2
Three turbos, two quattros, too much fun