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Oxygen Sensor Hack?

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Old 02-06-2009, 10:47 AM
visionseeming visionseeming is offline
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Oxygen Sensor Hack?

Hi all:
I have just been thinking lately, since the Oxygen Sensor is one of the more important sensors in a modern car that controls the air-to-fuel ratio, if one could generate a fake Oxygen Sensor signal, at will, that can make the engine run a bit leaner, this could improve FE for cruising situations, etc.

Quote:
How does an O2 sensor work?
An Oxygen sensor is a chemical generator. It is constantly making a comparison between the Oxygen inside the exhaust manifold and air outside the engine. If this comparison shows little or no Oxygen in the exhaust manifold, a voltage is generated. The output of the sensor is usually between 0 and 1.1 volts. All spark combustion engines need the proper air fuel ratio to operate correctly. For gasoline this is 14.7 parts of air to one part of fuel. When the engine has more fuel than needed, all available Oxygen is consumed in the cylinder and gases leaving through the exhaust contain almost no Oxygen. This sends out a voltage greater than 0.45 volts. If the engine is running lean, all fuel is burned, and the extra Oxygen leaves the cylinder and flows into the exhaust. In this case, the sensor voltage goes lower than 0.45 volts. Usually the output range seen seen is 0.2 to 0.7 volts. The sensor does not begin to generate it's full output until it reaches about 600 degrees F. Prior to this time the sensor is not conductive. It is as if the circuit between the sensor and computer is not complete. The mid point is about 0.45 volts. This is neither rich nor lean. A fully warm O2 sensor *will not spend any time at 0.45 volts*. In many cars, the computer sends out a bias voltage of 0.45 through the O2 sensor wire. If the sensor is not warm, or if the circuit is not complete, the computer picks up a steady 0.45 volts. Since the computer knows this is an "illegal" value, it judges the sensor to not be ready. It remains in open loop operation, and uses all sensors except the O2 to determine fuel delivery. Any time an engine is operated in open loop, it runs somewhat rich and makes more exhaust emissions. This translates into lost power, poor fuel economy and air pollution. The O2 sensor is constantly in a state of transition between high and low voltage. Manufacturers call this crossing of the 0.45 volt mark O2 cross counts. The higher the number of O2 cross counts, the better the sensor and other parts of the computer control system are working. It is important to remember that the O2 sensor is comparing the amount of Oxygen inside and outside the engine. If the outside of the sensor should become blocked, or coated with oil, sound insulation, undercoating or antifreeze, (among other things), this comparison is not possible.
If this is in fact true, if one could make a circuit that generates a signal that varies between 0.35 - 0.70 volts or so, and spends more time on the higher voltages, causing the mixture to appear rich to the ECU, making it lean it out a bit.

Anyway, this is all very hypothetical, and I have no idea how to implement such a circuit, but I was just wondering if anyone has and thoughts on this.
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Old 02-06-2009, 10:56 AM
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Re: Oxygen Sensor Hack?

There is a good reason why this isn't done, emissions. Lean burn engines produce a lot of NOx which causes acid rain. Specially designed engines have been made to minimize NOx production at lean air/fuel ratios. You can't just take a normal engine, run it lean, and expect clean emissions or good performance.
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Old 02-06-2009, 12:16 PM
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Re: Oxygen Sensor Hack?

Running a motor leaner than intended will cause it to run a smidge hotter... But I seem to remember DiamondLarry adding this to the list of mods on his Saturn using resistors (not for the faint of heart)?
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Old 02-06-2009, 12:19 PM
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Re: Oxygen Sensor Hack?

It's done in reverse for performance based engines to increase hp, richer fuel mixture is potentially more power although more waste too. If you increase resistance from the O2 sensor to the computer you can manipulate the signal in such a way as to fool the computer.

You run the risk of doing damage to engine and exhaust components if your modifications aren't precise and well thought out, consider first an increase in combustion temperature that may fatigue metal and lubricants.

It is possible to have a more FE based ratio than 14.7:1 and still allow mechanical performance to work safely.

If your going to follow these lines of modification start with a baseline dynamometer as your reference, tune within normal parameters without altering/modification, dyno again to see your results. Post these results and I'll offer some options, there are no quick and easy shortcuts.

If there were simple shortcuts, thousands of mechanics would have done do it since the 70's and those internet gadgets that are sold that produce fantastic results would actually work.

22:1 is not unobtainable as I think the lean burn engines are somewhere around there. This is an approximate 33% decrease in fuel consumption, I don't know what power output it produces but someone here I'm sure would be able to give specifics; I would learn the lean burn engines characteristics and emulate those safeguards and techniques. - Dale
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Old 02-06-2009, 12:32 PM
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Right Lane Cruiser Right Lane Cruiser is offline
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Re: Oxygen Sensor Hack?

Max, I don't think it was the O2 sensor... it had something to do with poor idling characteristics.

Dale, the Insight can go even leaner.
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Old 02-06-2009, 02:23 PM
visionseeming visionseeming is offline
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Re: Oxygen Sensor Hack?

Quote:
Originally Posted by Daox View Post
There is a good reason why this isn't done, emissions. Lean burn engines produce a lot of NOx which causes acid rain. Specially designed engines have been made to minimize NOx production at lean air/fuel ratios. You can't just take a normal engine, run it lean, and expect clean emissions or good performance.
Yes, I realize this, and considering Hellifornia has one of the highest emissions requirements, this would certainly have a negative effect on the environment, and the car would not meet the SMOG requirements. However, doesn't Honda make special catalytic converters for their vehicles with LB engines? Obviously, buying a new catalytic converter is probably too expensive to make the mod worthwhile, but something to consider.

Quote:
Originally Posted by drimportracing View Post
If you increase resistance from the O2 sensor to the computer you can manipulate the signal in such a way as to fool the computer.
Can you elaborate on this? As far as I know, one can use a resistor or a pair of resistors to lower the voltage of a signal, rather than to increase it.

Quote:
When the engine has more fuel than needed, all available Oxygen is consumed in the cylinder and gases leaving through the exhaust contain almost no Oxygen. This sends out a voltage greater than 0.45


According to the sources I have seen, higher voltages register as rich mixtures in the ECU, and thus increasing the signal's voltage should be the goal. On a tangent, it seems the actual frequency required for the signal is relatively low.

Quote:
When the computer receives a rich signal (high voltage) from the O2 sensor, it leans the fuel mixture to reduce the sensor's feedback voltage. When the O2 sensor reading goes lean (low voltage), the computer reverses again making the fuel mixture go rich. This constant flip-flopping back and forth of the fuel mixture occurs with different speeds depending on the fuel system. The transition rate is slowest on engines with feedback carburetors, typically once per second at 2500 rpm. Engines with throttle body injection are somewhat faster (2 to 3 times per second at 2500 rpm), while engines with multiport injection are the fastest (5 to 7 times per second at 2500 rpm).
I think the most effective way would be rig a signal generator that one would have on and off control, so it could be turned on when necessary, and off when the engine is cold or more power is needed. By off I mean the actual oxygen sensor signal should be used.

Still, a very theoretical idea, that may have unforeseen consequences.
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Old 02-06-2009, 02:43 PM
visionseeming visionseeming is offline
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Re: Oxygen Sensor Hack?

I found a site that explains the circuit required for a basic sine wave generator:

http://www.play-hookey.com/analog/si...generator.html

If one could design a generator the produces a signal similar to the upper right graph in the following chart, perhaps this could be used in leiu of the oxygen sensor signal.

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Old 02-06-2009, 03:07 PM
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Re: Oxygen Sensor Hack?

Quote:
Originally Posted by Maxx View Post
Running a motor leaner than intended will cause it to run a smidge hotter... But I seem to remember DiamondLarry adding this to the list of mods on his Saturn using resistors (not for the faint of heart)?
There is such a circuit and it's called an EFIE. It is not meant to be used by itself but with other modifications. Many of the so-called "fuel savers" probably actually do work but as the OP mentioned, the cars computer, through the O2 sensor, thinks there is a lean condition and adds more fuel canceling out what benefits the modification may have provided. As for the engine running hotter when lean, that's not necessarily true. It will tend to run hot if you try to put too much load on the engine while it's running lean. But, under light loads such as steady cruising or idling, the engine will actually start to run cooler simply because there isn't as much fuel to produce the heat. Too much fuel will also cause the engine to run cool because, as most people know, liquid fuel doesn't burn and too much of it int the air/fuel charge will have the effect of cooling.
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Old 02-06-2009, 03:22 PM
visionseeming visionseeming is offline
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Re: Oxygen Sensor Hack?

Quote:
Originally Posted by diamondlarry View Post
There is such a circuit and it's called an EFIE. It is not meant to be used by itself but with other modifications. Many of the so-called "fuel savers" probably actually do work but as the OP mentioned, the cars computer, through the O2 sensor, thinks there is a lean condition and adds more fuel canceling out what benefits the modification may have provided.
Wow. I can't believe I'm that stupid. It should be ridiculously easy to just add a constant voltage to the signal, that can be controlled by a POT. I think that's basically what a EFIE is.

Quote:
The EFIE is un-fooling the computer. All we want to do is get it back to giving us a 14.7 to 1 air/fuel ratio again. It should be noted that an oxygen sensor handling device, by itself, is not a fuel efficiency device. It possibly could be used to control the vehicle's computer, and make the engine burn a little leaner, and this could possibly give a small increase in gas mileage. But this is not what it was designed to do. It was designed to complement, and in some cases make possible, increased gas mileage using other fuel efficiency devices.
This does not make sense though, as the Oxygen sensor and ECU will faithfully do its job to maintain the 14.7 to 1 ratio, regardless of any mods that would increase the oxygen content. Increased oxygen in the exhaust IS the same as the engine running lean. Running lean will help mileage. Correct me if I am wrong.
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Old 02-06-2009, 04:19 PM
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Right Lane Cruiser Right Lane Cruiser is offline
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Re: Oxygen Sensor Hack?

Quote:
Originally Posted by visionseeming View Post
However, doesn't Honda make special catalytic converters for their vehicles with LB engines?
While you are correct, it is a little more than that (at least for the lean burn hybrids which do a good job of dropping down the NOX emissions). In those vehicles the NOX is captured by the (very expensive) catalytic converter. A wide band O2 sensor (also expensive) is needed for proper manipulation of the air/fuel mixture. Every once in a while the fuel mixture is enriched back to the more typical stoich ratio in order to "burn off" the accumulated NOX in the cat.

I'm not familiar with how the emissions are handled in an HX, but I do know that you can drop it out of lean burn with high load. This means that at the very least the wide band O2 sensor is needed.
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