Oxygen Sensor Hack?

Discussion in 'General' started by visionseeming, Feb 6, 2009.

  1. visionseeming

    visionseeming Well-Known Member

    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.

    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.
  2. Daox

    Daox Well-Known Member

    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.
  3. Maxx

    Maxx He who posts articles

    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)?
  4. drimportracing

    drimportracing Pizza driver: 61,000+ deliveries

    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
  5. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    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. ;)
  6. visionseeming

    visionseeming Well-Known Member

    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.

    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.


    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.

    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.
  7. visionseeming

    visionseeming Well-Known Member

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


    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.

  8. diamondlarry

    diamondlarry Super MPG Man/god :D

    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.
  9. visionseeming

    visionseeming Well-Known Member

    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.

    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.
  10. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    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.
  11. brick

    brick Answers to "that guy."

    Ugh. This is a good idea that keeps coming up, but never takes off for one reason: it doesn't work.

    Let's say you wire up your standard O2 sensor with a circuit to adjust the voltage so that the engine runs lean when you flip the switch. What happens on the other side of the loop? The O2 in the exhaust goes off-scale high and the O2 sensor stops providing useful information to the ECU. At that point you lose control of fuel enrichment because your instrumentation has essentially failed.

    Replace the stock O2 sensor with a wideband version and it's a different story.
  12. visionseeming

    visionseeming Well-Known Member

    In that case, wouldn't generating your own signal that doesn't exceed legal values help? As in have the signal fluctuate as normal, but make the peaks higher and the troughs higher.
  13. brick

    brick Answers to "that guy."

    Nope. The O2 sensors on a typical car work in too narrow a range. The mix is either just right or totally wrong in one direction or another. In order for the sensor to generate a signal that means anything, the mixture itself has to be right around stoichiometric plus or minus a little bit. Again, the wideband O2 sensor takes care of that problem. But you need to know what the mixture is in order to control it.
  14. brick

    brick Answers to "that guy."

    This diagram should help. (Yeah, MS paint!) The problem is how to deal with what happens after the black dotted line.

  15. visionseeming

    visionseeming Well-Known Member

    Ah, I understand. The A/F Ratio will not be controlled by anything. Constantly feeding in a signal that keeps the ECU thinking the mixture is a bit on the rich side(as in the average signal voltage is higher than 0.45) still does not necessarily mean the engine is running lean, and there is no way of controlling how lean it runs. I guess that ends this discussion then.
    Last edited: Feb 7, 2009
  16. drimportracing

    drimportracing Pizza driver: 61,000+ deliveries

  17. ccdisce

    ccdisce Member

    For the Ford PCM called EEC-V there are O2 offset tables available for hacking but the trim range is not much.
    Another way that I use is to hack into the average A/F table that the EEC uses when it goes Open Loop A/F and then hack into the conditions that enable you to get there so that you indeed get there. The Info Panel that I built confirms that I get there at 16.5 A/F. To save the CAT once the engine RPM gets above 1800 the EEC is programmed to go back to an average A/F of 14.8. The A/F profile is to start and idle at 14.8 2 with a second blend to 16.5 at 1100, and continue to 1800 before switching back to 14.8 and stabing the tps will drop the A/F back to 14.8.

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