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

In a message dated 12/6/99 2:42:33 PM Central Standard Time, 
isham-research.freeserve.co.uk@pop.freeserve.net writes:

> >>  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.  
> 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.
>  The MAC11/12D/14 cars have an initial overboost phase.  If you ask Scott
>  nicely, he might send you some graphs of initial boost he recorded when
>  blasting up and down desert roads in a 200TQ MAC14.  He shows a car
>  set up for 1.8 bar boost initially climbing to 2.03 bar after 1.63
>  seconds and decaying to the nominal 1.8 bar over the next 2.6 seconds.

I have experienced many readings that should have shut off a computer, modded 
or stock.  Look, overboost isn't a 2 second phenomenon.  Chrysler 2.2 turbos 
programmed overboost of 9 psi for 10seconds, then 7psi constant (that was a 
bosch EFI system too, in 1985!).  The audi S cars introduced this concept to 
the audis in 1992 with 15 seconds of overboost 2.1bar then 1.85bar constant 
on the Motronic.  A second or two of "recorded" boost anomolies doesn't sound 
like a "programmed" event, more an allowed event event.  I'll make sure to 
ask Scott M nicely, thank you, however, since I spoke with him extensively 
the other day, I think I'd rather ask you to nicely clean up your PT and 
"resistor" mod posts.  I'm intrigued by claims of 2.0PT with a 5v feed, being 
able to multiply the feed voltage by a factor of .3  :)

>  It's quite well documented in the microfiche for the MB (MAC12D) engine. 
>  The MAC12D has a maximum boost of 1.69 bar, but the ECU code quite clearly
>  allows it to go to 1.95 very briefly.
>  --
>   Phil Payne
>   UK Audi quattro Owners Club
>   Phone +44 7785 302803  Fax +44 870 0883933

2-3 seconds of an event, means that the computer will take some active 
measures to dial back an OOP (out of program) event before it shuts down the 
computer.  I've recorded totally stock computers that many times allow 1.6 
bar boost pressure to be read, then shut the fuel pump off at 1.5 bar.  
Calling this "overboost" really isn't correct (and it doesn't happen all the 
time either).  The computer will detect WOT, apply WGFV DC and look for a 
resultant reading, this isn't something that is absolutely linear in 
application, and has a delay.  Calling it "overboost" is misleading and 
incorrect, IMO.  1 or 2 seconds of measured boost above profile, isn't an 
"overboost" design. There are a lot of interesting things these computers 
will do in the real world that are measureable.  The warning really pertains 
to whacking a PT at or over 100% of it's rated capacity.  What audi is 
admitting to, is that the PT>ECU>WGFV loop circuit that controls a ramping 
turbo, needs some operational slack and production tolerance (all WG springs, 
engines and turbos are not created equal).  A TOTALLY different concept than 

Many misconceptions regarding the black boxes.  Many a tuner made a lot of 
money banking on this (resistor mods for big bux).  Suffice it to say, in the 
last couple of years, mostly by the efforts of this very list, the tuners 
work a bunch harder for your business, and black boxes are just identified 
circuits in a box that's black.

Phil, I ask *you* nicely, that we not send this thread back into the "wonder" 


Scott Justusson