need help with CIRCUIT ECU controlled O2 sensor enhancer

Discussion in 'Automotive Electronics' started by Mrusten, Dec 23, 2015.

  1. Mrusten

    Thread Starter New Member

    Dec 23, 2015
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    hello i got an interesting project but have no experience in designing a circuit

    so basic story is that i got an old volvo that get too much fuel with the new generation fuel, i think its bechause new fuel contanes more oxygen burn cleaner and leave more oxygen in the exhaust witch the O2 sensor pick up and the ECU think its running lean then compensate with more fuel.

    anyway how to solve this?
    i bought ostrich 2.0
    and did the steps in this forum:http://forums.turbobricks.com/showthread.php?t=227153


    it turns out that the ECU stay at what is thinks is AFR 14.7 that is 1 volt from the LAMBDA (O2 sensor) no matter what is done in the main fuelmap

    so now i can change the fuelmap and the ECU know what to do but get answer from the O2 sensor that say its all wrong! then compensate back to AFR 14.7 (1 volt at O2 sensor)

    an O2 enhancer can be used to fix this but then it will change the same value no matter load at the engine, and the engine need more fuel at a higher load to prevent pinging and self destruction.

    so my question here:
    Can anyone help me to design an citcuit that is controlled by PWM?

    Enhancer circuit: http://hydrogengarage.com/DIY/DIYinstructions.html
    [​IMG]
    this Schematic need to be controlled by PWM and i got only 1 O2 sensor so i only need one side of this circuit

    Circuit needs:
    -run from car voltage 9 - 17v
    -Enhancer for 1 O2 sensor
    -to be controlled by PWM
    -pot to adjust enhancer value at max dutycycle
    -pot to adjust enhancer value at min dutycycle
    -linear enhanser value between max and min dutycycle
    -pot to adjust dutycycle input bechause my measurements may not be corect
    -bechause the ECU vant to keep AFR to 14,7 the voltage from O2 sensor is 1v
    so the enhancer need to add or subtract in milivolts, how much volt totaly i dont know
    but it could be understood from the chematic of the enhancer


    wiring diagram of ECU and other stuff:http://ipdown.net/jetronic.info/tiki-index.php?page=LH2.4 Pinouts and Diagrams

    load signal is found on #8 on ezk(ignition) and #25 (LH2.4)
    here is EZK
    [​IMG]

    My measurements:
    signal peak to peak with reference voltage at ground: 1,406v
    time with at idle: 90 us
    time with at trottle (may not be full load): 416us
    square wawe PWM 2,404KHZ (this is a bit unstable but around 2,4KHZ

    dutycycle can be calculated some how from time with at trottle and 2,4KHZ same with idle

    the reason odd measorements is i got only a old ocilyscope and i have no training using it hehe

    pic from measuring load signal
    12395369_1671521946395880_626459814_n.jpg


    hopefully someone can help
     
  2. Mrusten

    Thread Starter New Member

    Dec 23, 2015
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    It is a mess im sorry
    just ask and i will explain.

    what is the easyest way to pwm controll a opamp to offset a signal voltage?
     
  3. #12

    Expert

    Nov 30, 2010
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    LM556 chip. Make a triangle wave. Use the other half of the LM556 to compare the triangle voltage with a DC level which you adjust with a potentiometer.

    ps, This is probably getting moved to the Automotive Forum. No big deal, just a protocol error.
     
    Last edited: Dec 24, 2015
  4. tcmtech

    Well-Known Member

    Nov 4, 2013
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    I'm highly skeptical of that theory being pretty much every small engine regardless of age I have that uses a modern fixed jet size type carburetor has required drilling the main jet out slightly to get them to run better and more efficiently.

    From my long experiences with deal with getting better fuel milage and power from emissions regulated EFI engines is to put a simple .3 - .4 volt germanium diode (1N34 series) in series with the stock O2 sensors signal output tricking the engine into running a bit richer not leaner.
     
    Last edited: Dec 24, 2015
    #12 likes this.
  5. #12

    Expert

    Nov 30, 2010
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    Here is a way to PWM but this drawing uses an op-amp to compare the triangle to a DC level.
     
  6. #12

    Expert

    Nov 30, 2010
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    Frankly brilliant! (If it works.)
     
  7. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Has worked for years on Fords to get rid of the damn throttle bog and pick up a noticeable amount of power and fuel milage. :D
     
    #12 likes this.
  8. #12

    Expert

    Nov 30, 2010
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    Yummy! I always buy Fords.;)
     
  9. Mrusten

    Thread Starter New Member

    Dec 23, 2015
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    it will not work in my case bechause my in my ecu there is no way to change the afr adjudted based on the o2 sensor. And i want different afr for different load to keep afr as close to knocking/pinging as possible.

    Thats why i need a circuit where offset can be adjusted at low load and other offset at high load then liniear offset values between this points
     
  10. Mrusten

    Thread Starter New Member

    Dec 23, 2015
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    Thanks but my skills is not high enough to make the rest of the circuit :(
     
  11. Mrusten

    Thread Starter New Member

    Dec 23, 2015
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    My car get too much allready and i think its the ethanol mixed and structure modifyed "inviremental friendly" frendly fuel's fault thats why i want to change afr according to tests
     
  12. tcmtech

    Well-Known Member

    Nov 4, 2013
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    If your O2 sensor is not controlling your engine once everything warms up either you have a bad O2 sensor or a problem elsewhere.
    But if you think you need to add voltage to the O2 sensors signal that to is not too difficult either. The easiest way is make a simple isolated DC - DC power supply that provides a small but stable adjustable voltage boost in series to the O2 sensors output signal.

    As for running your engines A/F mix even leaner I have serious doubts it will do anything gainful. The way things are as is running at stoichiometric A/F ratio is near the limits of being too lean to be good for a engine.

    I've worked with alternative fuels for years and I have done every imaginable hack known relating change the stock A/F ratios on vehicles and not once has the theory that running super lean makes things better proven itself to be true. Especially so with the more modern fuel mixes.

    Now for what your O2 sensor signal should look like (when the system is working properly) it should be a fairly stable rising and falling waveform going between ~ .1 and .9 volts with a 2 - 4 Hz frequency if the ECM and all other sensors are working right.
    If not that's why you are getting the constant ~1 volt (12+:1 high rich A/F ratio) and not the oscillating signal that should be centered near .4 - .5 volts at the 14.7:1 A/F ratio.
     
  13. Mrusten

    Thread Starter New Member

    Dec 23, 2015
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    New fuel = more oxygen in the exhaust
    more oxygen = engine compensate by more fuel
    more fuel= to get the stock afr "correct"
    Stock afr= adjusted to fuel that give less oxygen in the exhaust thats why it all going fucked with norwegian special fuel.

    i dont know if its the same fuel elswhere but the collor of norwegian fuel this days is like water and not much smell of bensin

    there you go the answer is not to add fuel!

    I want to measuer exhaust temp and knock then test drive and adjust afr til it is within reasnoble limits

    about o2 sensor voltage i was reading that the ecu want to keep 1 volt average but it may be wrong
    i didnt measure mine cos its eaven running rich with stock fuel map and open loop. New fuel demand less fuel to the engine it make sence
     
  14. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    The "new fuel" oxygen would/should be consumed in the cylinder when burned, that's it's purpose. It seems to me that your problem is bad injectors. They are dirty and not closing all the way, giving fuel even when they should be 'closed'. The other give away to this is the first post saying "an old volvo", any brand car that is 'old' can have this happen.
     
  15. Mrusten

    Thread Starter New Member

    Dec 23, 2015
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    tja if thats the case it would try to compensate by giving less fuel to the engine.

    now after i modefyed my fuel map to a lot less and then permanent run in open loop the engine is running more steady and smoodely and uses a lot less fuel.

    if this was the case in closed loop it would keep my changes in the fuel map but it do not! it change back to get too much fuel.
    only way this can happen is if there is a too clean burn where emissions is not as it was when the bosch LH2.4 was invented in the end of 80's

    give me the damn circuit and stop arguing please

    no my o2 sensor is fine!
    and there is no exhaust lekage to add oxygen in the exhaust before o2 sensor eather
     
  16. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Can we assumed you forced it to a too rich and too lean conditions to ensure the sensor is operating properly?
     
    Last edited: Dec 26, 2015
  17. Mrusten

    Thread Starter New Member

    Dec 23, 2015
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    Like i said new lambda new amm new temp sensor.

    the same problem in constant on most cars fitted with the lh2.4 injection system

    so its down to the fuel really.
    i want to improove a bit and have closed loop engaged for longer and have variable afr according to test and measurements.

    i try to understand opamp circuit and i wonder if its possible to convert pwm to voltage then feed it to a opamp that add/subtract volt from the o2 sensor input
    offcorse with small pots to adjust
     
  18. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    I take it that is a wideband A/F ratio O2 sensor?
     
  19. Mrusten

    Thread Starter New Member

    Dec 23, 2015
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    Yes but i will use the narrowband output with the wideband specter
     
  20. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Everything I've seen about the wideband AF ratio O2 sensor says it's characteristics are opposite of the old standard sensor.

    Have you induced a rich and lean conditions and observed the outputs? Under normal conditions the wideband ideal is around 3.x V and the older O2 sensors is about 0.45V.

    Which sensor (model number) are you using and do you have the output specifications ? It appears you want a level translation. If you want to go from 2 to 4 volts (wideband A/F O2 sensors) to 0.1 to 0.8 volts, it can be done.

    There are plenty of youtube videos out there describing the sensors, what their outputs look like, and how to test them. By testing them, I'm not saying yours is good or bad, but how their output responds to varying stimuli. The display on your oscilloscope didn't look like any that were on the youtube videos.

    Put yourself in the shoes of those here that might be willing to help you ... for no compensation. What do you think the first words in my mind were when I read it?
     
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