Oh... one more tidbit...
On a dual sensor setup, the pre cat and post cat sensors are different. The
post cat sensor is adjusted to compensate for the effects of the exhaust
gasses passing through the platnum in the catalytic converter (which
converts carbon monoxide to carbon dioxide).
So, youre still dealing with 2 sensors sending out the same voltages (or so
I think)
Gary Hedlin
""Gary Hedlin"" <ghedlin@theramp.net> wrote in message
news:ateo8o$89l$1@bent.twistedbits.net...
>
> If i'm not mistaken, It was explained to me that the reason for the 2
> sensors is because the PCM reads both of the voltages sent from the two
> sensors and determins the richness / leanness of the air to fuel ratio.
If
> sensor two reads the same as the first one, the PCM will take that number
> and adjust the air to fuel ratio accordingly.
>
> I had a situation a while back where one of the sensors was bad, and was
> tripping the check engine light. You could tell the air to fuel ratio was
> rich because of the disttinct gas smell I got from a day of gunning it at
> the strip. If one of the sensors are bad, your MPG's will go straight to
> hell.
>
> The theory behind Bernd's cat box is to emmulate the voltages sent by the
o2
> sensors. I doubt however its just a resistor in a pretty box. Annyway,
if
> the PCM is reading the voltages, and theyre the same, the PCM thinks
> everythings A-OK and put out the default air to fuel mix. I doubt the
PCM's
> default is "performance freindly", rather set for emmissions. I think it
> would be cool to make a cat box that could be adjustable, so you can make
it
> rich for performance needs, and lean for everyday driving.
>
> So, bottom line, the o2 sensors are there for a reason. Since the
> tree-huggin hippies won't let us run good ole
> carbs anymore, there has to be a way of adjusting the air to fuel ratio
> thats 10 times harder than it should be. Oxegen sensors are just the best
> way to do that while the parts people can rape us for the privledge of
being
> "ozone freindly".
>
> Gary Hedlin
>
>
>
> <jon@dakota-truck.net> wrote in message
> news:atejo3$5ed$2@bent.twistedbits.net...
> >
> >
> > How about a good old fashioned DML engine theory discussion? :-)
> >
> >
> > The Magnum engines all have a Y pipe with the oxygen sensor placed
> > right after the Y. This is obviously a good place since the sensor can
> > sample both banks of the engine, and it is close enough to the engine
> > to be able to compensate for A/F ratio changes quickly.
> >
> > It becomes a problem when changing to a dual exhaust setup. The
> > generally accepted theories on what to do with the exhaust sensor in
> > a dual exhaust are to put it in (or after) one of the downtubes (in
> > which case you pretty much assume (hope) that both banks of the engine
> > are running at the same A/F ratio), or to put it in the H pipe or X
pipe.
> > Some people have said they haven't been able to get a good reading from
> the
> > H pipe, though I imagine right in the middle of an X pipe would not
> > have that problem.
> >
> > The problem with the first solution is that you are only sampling one
> > side of the engine. This could cause a problem if for some reason the
> > side of the engine with the O2 sensor in it was rich but the other
> > side was lean. (Perhaps due to the crossover tube on the fuel rail
> > being restricted?) The computer would see the engine as rich and lean
it
> > out some more. Not a good thing for the already lean side of the
engine.
> > (This is actually how my Barracuda is currently set up, as this is what
> > most people do...)
> >
> > The problem with the H/X pipe solution is that it only works if
> > you have an H/X pipe. I was lying under my Ram today and had some ideas
> > for the exhaust but an X pipe did not look like a viable solution.
> > (In order to have enough room for an X pipe with what I want to do,
> > the exhaust would need to hang under the frame where it would be
> > subject to being smashed up (4x4). Also, the H or X pipe is often
> > back a ways - this might be too far from the engine for the computer
> > to respond to A/F events in time, or might cause the computer to be
> > constantly overcorrecting (porpoising).
> >
> >
> > It seems to me that if it were possible to use 2 oxygen sensors,
> > both of the above problems would be solved - the catch is how to pull
> > it off? One idea would be to just take the O2 sensor connector and
> > Y each wire to create two connectors. I would guess this would work
> > OK for the ground wire and the two heating element wires, but what about
> > the signal wire? If both O2 sensors were reading 0.5v, what would be
the
> > reading be at the computer? 1v? 0.5v? none of the above? I have not
> > tried this so I'm not sure - what happens when two voltages come
together?
> > Do they add together or try to equalize at the same voltage or what? I
> > know that when you wire two batteries in parallel, the strong battery
> > discharges and the weak charges until they equalize at the same voltage;
> > would the same thing happen with the oxygen sensors?
> >
> > The above idea seems so simple that if it actually worked, everyone
> > would be doing it. So, I'm assuming it won't work to just tie the
> signals
> > of 2 oxygen sensors together. What about a circuit (either analog or
> > digital) which would generate a true average of the signals?
> >
> > If I remember right, 0v would be full lean and 1v would be full
> > rich. If that is the case, what about a variation of the above idea
> > where a circuit would pass through the lowest signal to the computer?
> > (For example, if the left O2 sensor was reading .6v and the right was
> > reading .7v, the .6v signal would be allowed to pass through to the
> > computer.) The idea there of course being to send the leanest signal
> > of the two to the computer to keep the engine safe (too rich is better
> > than too lean).
> >
> > Another variation of the above idea is a circuit which would
> constantly
> > shift between the two sensors. It would essentially be a switch which
> would
> > pass through the left O2 signal, then after X amount of time, allow the
> > right signal through instead, then after X amount of time, back to the
> > left sensor. The X amount of time would need to be determined, I would
> > suspect somewhere in the 1-5 second range?
> >
> >
> > Some of the above ideas I am not sure would work, but some of them
> > I am fairly certain would work (it would just be a matter of building
> > it right). So... Does anybody have any experience, ideas, opinions,
> > etc. on any of the above?
> >
> >
> > --
> >
> > -Jon-
> >
> > .---- Jon Steiger ------ jon@dakota-truck.net or
> jon@jonsteiger.com ------.
> > | I'm the: AOPA, DoD, EAA, NMA, NRA, SPA, USUA. Rec & UL Pilot -
SEL
> |
> > | 70 Cuda, 90 Dak 'vert, 92 Ram 4x4, 96 Dak, 96 Intruder 1400, 96
FireFly
> |
> > `------------------------------------------
> http://www.jonsteiger.com ----'
>
>
This archive was generated by hypermail 2b29 : Fri Feb 06 2004 - 11:48:14 EST