# Nissan Pathfinder (1991) Oxygen Sensor



## cfb (Apr 3, 2011)

This is a general question that hopefully applies to most (if not all) vehicles that have oxygen sensors. 

I'm interested in seeing if I can convert my Pathfinder to "Flex Fuel" by simply intercepting the pulse to each fuel injector and widening it by some percentage, depending on the gasoline to ethanol ratio. 

For optimum results, wouldn't one make final adjustments to the pulse width based upon the oxygen sensor readings? (Isn't that what the oxygen sensor is ultimately for? To not run with a fuel-to-air ratio any richer than necessary?

From a practical standpoint, does anyone know what the output voltage (or resistance?) range of the oxygen sensors are, and how that translates into whether to increase or decrease the fuel injector pulse width, and by how much?


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## jdg (Aug 27, 2009)

Doesn't work that way, not even close.
Oxygen sensors do measure the oxygen content in an air stream, but only in a certain SPECIFIC range which, in this particular case, is peculiar to gasoline.
Besides the needed computer workings, engines designed to run on gasoline (or 10% in some parts of the country) don't like running on E85 simply because the seals/o-rings/etc will get eaten up by the ethanol and the resultant extra water in the fuel since ethanol is hygroscopic.


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## cfb (Apr 3, 2011)

*Oxygen Sensor*

Hi jdgrotte and thank you for your response. Although I can accept there is something to be learned here, like most engineers I may need more information to be convinced. (Like the day we got a new copier and one of the secretaries put a sign on it to not make copies with the cover open. If she'd gone on to say because it's interpreted as pitch black by the copier and that consequently gums up the drum, we all wouldn't have immediately began conducting our own experiments... )

Oxygen Sensor. I'd have thought the ideal stoichiometric mixture would leave NO oxygen in the exhaust stream (whether running on gasoline, ethanol, or some combination or both.) However, the practical side of me accepts that will probably never happen, and there will always be some - albeit "less is better" right up until you're running lean (which I then suppose causes your engine to run hotter and consequently does bad things to exhaust valves and generates more oxides of nitrogen - although I do have a quick solution for that too!)

The fact that there's an oxygen sensor AFTER the catalytic converter tells me something too - such as they're testing for a rich mixture being consumed by a WORKING catalytic converter and not being dumped into the atmosphere perhaps?

But insofar as o-rings and seals, I've read that Brazil (where they're making a very serious attempt to get off of foreign oil) had that problem early on, and consequently an entire generation of vehicles was destroyed in the interim - but that was due to the "abrasive" nature of the ethanol, which destroyed the jets in carburetors and fuel injectors. But they did manage to find long term solutions the problems somehow - I'm just not up on the details.

My own personal sentiments are that my 1991 Pathfinder becomes sacrificial - at least if I can't maintain it with the occasional replacement of destroyed parts - when compared to the bigger threefold problem of not only the greatest transfer of wealth (out of our pockets and into theirs) in the history of the human race, not only to "big oil", but far too much of it ultimately to our enemies - one of which seems head and shoulders "bent" on developing a weapon or two, no doubt for the ultimate purpose of someday taking out however many of our most significant cities. (And if there ever was any question, as the rest of the civilized world rethinks nuclear power after Japan's experiences, how much of that quality "rethinking" is going on in that part of the middle east right now?)

On that scale, perhaps the ones who "shouldn't breed" are the ones who mindlessly facilitate these painfully obvious eventualities instead of pursuing other less harmful options (although I know I'm just as guilty as the next guy for shopping at "Wally World" in full support of people who by the looks of things will someday be sinking our entire aircraft carriers with a single missile! Maybe someday I can teach my kids better - but then again maybe by then it won't matter anyway!?)

But all that aside, might you be able to explain HOW a simple straightforward oxygen sensor can somehow manage to distinguish WHAT is being burned - from the perspective of oxygen levels - as if to suggest that a stoichiometric mixture of gasoline and air would somehow be distinct from a stoichiometric mixture of ethanol and air? (If so, there is most definitely something to be learned here!)

Peace!


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## jdg (Aug 27, 2009)

cfb said:


> Although I can accept there is something to be learned here, like most engineers I may need more information to be convinced.


Then...do the research. I'm not going to spend all day trying to convince you that you've got nowhere plans.



> Oxygen Sensor. I'd have thought the ideal stoichiometric mixture would leave NO oxygen in the exhaust stream


Nope, the oxygen sensor tells you how much FREE oxygen is in the exhaust stream. There's always oxygen in the exhaust stream...whether it's busy being tied up with nitrogen, carbon, or otherwise is dependant on the running conditions.



> The fact that there's an oxygen sensor AFTER the catalytic converter tells me something too - such as they're testing for a rich mixture being consumed by a WORKING catalytic converter and not being dumped into the atmosphere perhaps?


ECU's don't shoot for a perfect air/fuel ratio 100% of the time. They swing back and forth, say 95% - 105% of the perfect amount of required fuel. The Cat absorbs extra O2 when it's lean, and releases it when it's rich. The front O2 swings wildly back and forth from rich to lean. The rear O2 sensor, assuming the cat is working properly, stay relatively steady. If the cat was bad, and/or going bad, the rear O2 sensor will start to swing along with the front one.



> I've read that Brazil.....


The first words of last thoughts...
So much for that...



> But all that aside, might you be able to explain HOW a simple straightforward oxygen sensor can somehow manage to distinguish WHAT is being burned - from the perspective of oxygen levels - as if to suggest that a stoichiometric mixture of gasoline and air would somehow be distinct from a stoichiometric mixture of ethanol and air? (If so, there is most definitely something to be learned here!)


It's not so much being able to tell how much is being burned where, what's being burned (or not burned), and how much crap is left over.....It's more a matter of the programming in the ECU and the fuel system components being able to compensate for the varying needs of the engine under different operating conditions. Ethanol = less BTUs per unit mass when compared to gasoline, therefore requires X percentage more of it injected. Will the ECU dump a code because the X percentage more is out of it's programmed tolerance? Who knows...I'm guessing yes. Will it drop back to open loop where it'll just keep injecting the same amount of ethanol as gasoline and thereby render the air/fuel ratio EXTRA super lean? Could happen.
And, aside from that, are your fuel system components able to handle the lack of lubrication properties that gasoline has which ethanol does not have and/or will they handle the increased amount of dissolved water in the fuel that hygroscopic ethanol will eventually introduce, or will your fuel lines become 15ft of 1/4" rusted tubing...
And besides all that...stoich for gas is about 14.7:1.
Stoich for ethanol ISN'T 14.7:1, it's something like 9.6:1 give or take.
It takes roughly 53% more ethanol (actually E85, by weight) than gas to get roughly the same power.
Does that translate to roughly 53% less MPG or 53% less horsepower? Of course not. Nothing translates 100% directly. But it is markedly less.
Don't get me wrong. I've got nothing against ethanol, E10, E85, or even E30. I just figure it's trading gasoline in your car for the diesel required to run the farm equipment and the coal for the electricity to process the fuel. Basically, a less than zero sum game.


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