Re: toasting an O2 sensor, hesitation at boost, and more

[QSHIPQ@aol.com]

In a message dated 12/6/99 1:37:46 AM Central Standard Time, 
isham-research.freeserve.co.uk@pop.freeserve.net writes:

> You're wrong.  Most transducers continue to give relatively predictable
>  output up to 30% above their rated capacity.  That's how the 'voltage
>  divider' mods work, and there are very many of them running around
>  without problems.  Almost all, perhaps even all, of the PT failures I
>  see are caused by fuel contamination, not over-ranging.

Not my understanding of the audi PT Phil.  In fact, testing a 2.0bar PT, I 
got max voltage below 2.0bar.  The predictability of the output may be good 
up to 30% over rated capacity, but the output is the same, 4.9 volts.  In my 
understanding, voltage divider mods don't work that way.  Voltage dividers 
divide the signal from the PT.  So, let's for sake of argument assume that .5 
* 2.0 bar is 0 boost/vacuum = 2.95v.  A voltage divider mod that give is 75% 
of actual readings means that at 2.0bar the comptuer is interpreting 3.675 
volts instead of 4.9volts at 2.0bar.  Or more specifically, at 2.0bar actual 
boost pressure, the ECU 'thinks' it's only 1.5bar (no messing with the 
overboost cutoff is necessary either).   A Bosch/audi PT can't differentiate 
any signals over 100%, so it doesn't know the difference between 2.0 and 
3.0bar.  Why do you think the stage III mods of the S cars (26psi altitude) 
need to get a 3.0PT?  According to your information (22.5 * 30%) + 6.75 = 
29.25psi, easily done with a 2.5 bar PT isn't it?  Are you sure you have this 
right?  Right now the all 2.0bar chip mod derivitives use 1.95bar as the top 
reading.  Why is that?  

>  Not perhaps in list circles, but I've seen two that were less than two
>  months old in the last week.

Here in the US, I know of none.   That would include all QLCC vendors, and 
TAP, and Hoppen and IA.

>  The microfiche is even more disparaging.  However, that doesn't alter
>  the fact that they are either disconnected or the owners are told
>  to apply mental corrections.  I'm describing what I see, not disserting
>  on ideal boost gauge configurations.

Do note, that there are 2.5 bar 10vt boxes running around that read correctly 
on the boost guage.  The guage readout can be configured differently than the 
PT divider circuit to the chip.

>  
>  Note that the microfiche consistently warns _AGAINST_ reading peak,
>  because of the deliberate overboost programmed into the MAC11/12D/14.

?  What "overboost"?  Maybe a description of overboost is necessary.  The S 
car motronic started the overboost era in the audi computers, not before to 
my knowledge.  Are you referring to altitude compensation?  That isn't an 
overboost phenomenon.  That's an altitude compensating (absolute boost) 
concept.

Scott Justusson