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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