Re: Dual O2 sensor ideas...

From: Mike Meyerhoff (mike@mypants.org)
Date: Sat Dec 14 2002 - 09:26:34 EST


I don't think it'd work by averaging :( . The 02 voltages jump all over the
place. An averaged value would jump all over too, but have a diferent
range.

For instance (roughly)... if one sensor can read from 0.0 - 1.0 volts.
When you average two sensors together you probably would not have many 0 -
0.2 and 0.8 - 1.0 readings so your range would be 0.2 - 0.8. That change in
range might not work well with the computer.

What might work better would be a setup where each sensor was read every
other time, alternating. How you build that bit of electronics I have no
idea, wrong engineering degree :)

mm

>
>
> 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 ----'



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