Re: O2 sensors

[PDQSHIP@aol.com]

In a message dated 96-12-09 12:48:31 EST, you write:

<< Subj:	Re: O2 sensor Primer
 Date:	96-12-09 12:48:31 EST
 From:	graydon@apollo.gmi.edu (Graydon D. Stuckey)
 Sender:	owner-quattro@coimbra.ans.net
 To:	STEADIRIC@aol.com
 CC:	shields@tembel.org, quattro@coimbra.ans.net
 
 On Mon, 9 Dec 1996 STEADIRIC@aol.com wrote:
 
 > >why.  I can't believe its the heat since rotary engines produce even more

 > >heat with no loss in O2 sensor life.  I don't _think_ excessively rich 
 > >mixtures will reduce the lifespan too much, but I was wrong once or twice

 > >before...  :-)  (Contrary to Bob D's belief  :-)
 > 
 > No Leaded Fuel here Graydon.  I'm Thinking Heat, Flow and velocity.
 
 OK then, per my discussion above, I don't think its heat, (rotary exhausts
 run at 2000 deg F) so what else is there?  I'll have to talk to someone
 who knows this stuff.  FLow and velocity are possible culptrits, since the
 sheer mass of airflow would possibly cause refernce gas contamination
 earlier.  Maybe there's some thing else Eric's not telling us?  >>>>>>>>>

Hmmm, in this late, but maybe can add a few sense....  O2 life depends on
element exposure, eric is right...  the optimal temp range for O2's is 650 to
850 degrees F, would doubt the rotory measures that high 2000 at the O2
graydon, tho I have measured 1500 at the O2 on PDQ before exh mods......
 Something regarding flow....  Every tweeked 5L mustang with efi and tweeked
exhaust components loose not only gasmileage, but warrantees too....  It
seems that reduction in backpressure sends too much flow  at the O2 and that
gives the computer an "outside" window reading, that sends the computer to
limphome mode, which is, thankfully here, max fuel....  Constantly firing
flames at the O2 reduces it's life too, which is the main reason for NOT
adding a pop to atmosphere valve to the turbo, ala TAP, or running too rich
fuel mixtures....  If you look at an O2 it has a design that grabs exhaust
gasses in it's turbine... But, like a turbine if you increase velocity to a
point, it becomes an inefficient wing, i.e. the pressure on the wing becomes
so high that there is no longer a low pressure area, velocity.....  The best
place to mount one....  In the cat, hollow or full, since this is a chamber,
and by definition a pressure drop, velocity and flow are less affecting....
 Amazingly enough, CATS are designed to work in the 650 to 850F range, and
most are mounted forward enough to assure this, but with 3 wire it's
irrelevent anyhow....  

Eric knows that headers, turbos and freeflow exhausts can wreak havoc on the
O2 system...  Ford learned it the hard way...  So did I, btw, btdt....  Heat
is a necessary component of proper O2, but a 3 wire O2 just forward of
honeycombs is just fine....  To put it close to the turbo, or in the header
is OK too, but the gains are not faster O2 readings all the time.....  With
the tweeked charge air cars a lot of us own (both of yours graydon) this
deserves some investigating....  My O2 is only a cyberdyne reader anyhow, so
don't matter where I put mine....  Creating a low pressure area in the
exhaust is not as hard as one would think....

Scott