DGUY, Don, Mr. Guy YO, Hey!!!!!

[FieroBUZZ]

Enjoyed the read on duals.  I am doing that to my 3800 so I can ditch the crossover pipe.  Info sharing welcome..  

[dguy]

I take it you mean my little exploration into single-to-dual O₂ sensor conversion on PFF?    (this thread for anyone who's curious)

I haven't had the opportunity to try it yet; I'm waiting for my (stock) muffler to fail, which will provide a convenient excuse to start making a mess of the exhaust system.  

I have a design in my head for the 2.8, which I don't imagine would be too painful to modify for the L67.  Exhaust from the front cylinder bank would more or less follow the original routing, except for a conspicuous lack of y-pipe.  i.e. Manifold->downpipe->cat->tailpipe.

The rear bank would take a tight 180 off the manifold, pass through a separate cat in the original muffler location, then another tight 180 and on to a tailpipe.  Theoretically if it's too loud, there'll still be room to fit in a pair of these (or similar) in there without butchering the trunk or compromising ground clearance.  If it turns out that there isn't enough space, a set of those ugly little
SuperTrapp tips should cut back on the noise.  However if I like the noise with cats-only (must be the biker blood), I have a plan for those megaphone tips you gave me last (?) year which is a bit unusual.  No, I'm not telling... yet.    

The only thing I haven't decided upon yet, is whether or not to plumb in a T off the rear bank and keep the EGR, or have someone burn a chip for me with all of the EGR-related code disabled.    I haven't seen the L67 often enough to know where the EGR plumbing fits in to the exhaust system's geography, so I really don't know what I'll do with it when that day comes.

[aaron88]

The information in the PFF thread isn’t accurate and the diagram doesn’t resemble an O2 sensor circuit at all.

Basically if you want to run two O2 sensors in parallel you can just do so and get the higher voltage.  But I’m not sure how an O2 sensor reacts when you backfeed a voltage to it. For example:

If you had one bank running rich and the other running lean, (which wouldn’t likely happen, but your O2 sensor may think so) so one O2 sensor reads .55 volts and the other reads .45 volts.  What happens is the ECM sees the .55 volts and he other O2 sensor would get a back voltage of .1 volts (effectively charging the O2 sensor just as your alternator charges your battery).  It’s not likely that this will damage an O2 sensor but there is more to consider as well.

Lets say that both sensors had the same voltage (which is also not likely, but lets say that this is a perfect world and every O2 sensor is built with exacting tolerances).  The ECM would see twice the current potential than it was designed to see.  Will this hurt the ECM?  I don’t know and I wouldn’t think so, but doubling the current available to a computer is enough to raise my eyebrow.

So lets say that the computer is okay with the extra current available and you add a diode to each O2 sensor.  All you have accomplished is that the computer is going to read the riches bank, and lean out the mixture.  I would think that you wanted the exact opposite.  I personally would want to read the leanest bank so that the computer could add more fuel.

So what you really need is a circuit that will compare the two voltages and feed the lowest one to the ECM.

This means that you want to do some research on circuits that compare voltages.

Aaron

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[dguy]

The information in the PFF thread isn’t accurate and the diagram doesn’t resemble an O2 sensor circuit at all.

That's because it wasn't supposed to resemble the O₂ sensor circuit.    It was an example of how to arrange multiple voltage sources, with equal loads, such that the potential across the combined circuit was the average of all sources.  I thought that I had made that clear?  

But I’m not sure how an O2 sensor reacts when you backfeed a voltage to it.

Apparently this happens all the time.  "Also, the ECM apparantly applies voltage to the sensors, but basically if you add resistors you shift the voltage the ECM sees and that will drive the mixture out. Not sure how to handle that one."

Also like I said in my reply to Jazzman, applying a voltage to a sensor which generates a voltage sounds just... plain... weird.  Counterproductive even.  

If a voltage averaging circuit between dual O₂ sensors would work, I have no idea what will happen with respect to the alleged application of voltage to the sensors by the ECM.  This is also something I thought that I had stated clearly when I addressed Jazzman's reply.

Lets say that both sensors had the same voltage (which is also not likely, but lets say that this is a perfect world and every O2 sensor is built with exacting tolerances).  The ECM would see twice the current potential than it was designed to see.  Will this hurt the ECM?  I don’t know and I wouldn’t think so, but doubling the current available to a computer is enough to raise my eyebrow.

...which is why I never had any intention of hooking this up to the ECM without first trying to determine what its current tolerances are.  Trust me this isn't a blind, slap-it-together-and-see-what-happens forray.  Anyone who believes it to be such needs to work on their reading comprehension skills.  

So lets say that the computer is okay with the extra current available and you add a diode to each O2 sensor.  All you have accomplished is that the computer is going to read the riches bank, and lean out the mixture.  I would think that you wanted the exact opposite.  I personally would want to read the leanest bank so that the computer could add more fuel.

Here's where our opinions differ.  

Remember, the stock ECM is expecting a signal from a single sensor, which sits in the exhaust stream at a point where the exhaust from both cylinder banks has already been merged.  Imperfections in the exhaust flow from each bank aside, the original O₂ sensor is already providing a signal to the ECM which represents the average oxygen content in the exhaust gasses of all six cylinders.

...which is why IMO in a cross-overless system which has been fitted with one O₂ sensor for each bank, I believe that you should be averaging the two signals before passing them on to the ECM.  Its programming was implemented around the expectation of an averaged signal, not a "richest bank" or "leanest bank" signal.


On the other hand, I also think that the idea of one O₂ sensor per cylinder bank, fed separately to an ECM which was designed for dual O₂ inputs, could have additional benefits were the said ECM also able to separately control the injector pulse width for each bank.    ...but I really don't feel like embarking on a re-design of the ECM, or programming of it at the moment.