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  • fuel mixture.

    this is a foolish question:stupid: but:

    has anyone hooked a DVOM to the oxygen sensor, and recorded the highest voltage registered, while in open loop at operating temp, and in closed loop, at operating temp.
    All at WOT?

    If you have, please list s14 size, and management type.

    I realise that voltage depends on temp and that this is inappropiate for tuning, but humour me.
    m

  • #2
    Bosch narrow band lambda sensors (aka oxygen sensors, O2 sensors) read about 150 mV for lean to 850 mV for rich. They are pretty much a boolean indicator, as they only have resolution between lambda values of 0.99 to 1.00.

    Lambda represents the "excess air factor", or the ratio of actual Air/Fuel ratio to stoichometric A/F ratio. So a lambda value of 1.00 represents an A/F ratio of 14.7. A lambda value of 0.99 represents an A/F ratio of 14.55 (14.7 * 0.99).


    Dean

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    • #3
      cheers Dean.
      I've been experimenting with open loop/ closed loop, trying to match a pattern of sluggish behaviour to Mixture quality, plus determine just how fit the O2 sensor is.

      I see better average mixture in warm open loop with dither hovering narrowly between 0.35 - 0.80v warm cruise. The car/engine runs smoother/zestier in open loop but i'm risking the cat.

      Closed loop warm , we see dither from 0.23 - 0.82v with a soft tug/surge behaviour . irritating especially in coast and moment the TPS closes..

      When running poorly in open loop, car exhibits coarse engine with very little dither/deviation from 0.68v.

      Max spike WOT is 0.89 warm open loop and 0.904 in warm closed loop.

      Seems O2 sensor is ok, but getting on in age.

      I'm not too worried about converting to mixture ratio as the voltage is temperature dependent.

      m.
      Last edited by Mmark; 07-18-2004, 01:44 AM.

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      • #4
        Originally posted by Mmark


        The car/engine runs smoother/zestier in open loop but i'm risking the cat.


        m.
        There is a reason for that. There are numerous sensors that the Moronic needs readings from before firing the injectors. Of course the O2 is the last in the chain of events, hence the better/quicker response of the throttle, if it is removed. It is running somewhat richer all around but not by much. Another reason it has a quicker response is the estimating the Moronic has to do for the accel enrichment. The TPSwitch is not part of the equation, just the RPM load cell and the fuel load cell. This is why the Moronic has a lean spike on every throttle input up to a certain RPM/load. You really should get a WBO2 if not just for watching how the Moronic fuels the car in different situations. There are several situations where the on/off TPSwitch combined with an aftermarket chip may cause unwanted fueling on the bad side if you know what I mean.

        As for the narrowband O2 sensors not being very accurate off of stoich, I have to disagree if the algorithms are sufficient. The LENZ is suprisingly accurate at all AFR's from dead rich (10's) to wayyy lean (18's) with just the NBO2 input according to my FJO WBO2.

        T

        Comment


        • #5
          Mmark, it sounds like you're chasing drivability problems. 90% of fuel related problems occur within the ignition system. So check the cap and rotor, the wires and the plugs.

          After ensuring the ignition system is working as designed, adjust the valves, set the base idle, synchronized the throttle bodies and set the base CO. This will make a world of difference.

          HANDBLT, I was talking strictly about the narrow band O2 sensors when I said that they don't have much resolution off of stoichometric. I learned this from the Bosch Motronic technical instruction manual and "Bosch Fuel Injection and Engine Management" by Charles O. Probst, both available from http://www.bentleypublishers.com (on the Bosch page). A wide band O2 sensor can represent 10:1 to 18:1, but a narrow band O2 sensor can't.

          I know it's possible to get a wide band O2 sensor and a control unit that will mimic a narrow band O2 sensor for the Motronic unit and also provide the actual A/F ratio. Is this what you have?


          Dean
          Last edited by Dean; 07-18-2004, 09:03 AM.

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          • #6
            Thanks guys.
            It is an intermittent drivability problem that looks fuel related as all ignition components except coil are new. So it seems that my fueling ocasionally lags, so I should reset base CO and probably synchronise the throttle bodies as well as look for a small unmetered airleak.

            I'd hate to lose the engine, and the car is a DD/track rat, so I've been concerned about lean running.

            I wanted to verify that the engine is getting a decent mixture at WOT from any engine speed.

            has anyone tried the old raise the spring tension in the fuel pressure regulator trick? (crushing the spring housing slightly to raise fuel pressure.)
            It worked ok on a factory injected zetec.
            m.

            Comment


            • #7
              Originally posted by Dean


              HANDBLT, I was talking strictly about the narrow band O2 sensors when I said that they don't have much resolution off of stoichometric. I learned this from the Bosch Motronic technical instruction manual and "Bosch Fuel Injection and Engine Management" by Charles O. Probst, both available from http://www.bentleypublishers.com (on the Bosch page). A wide band O2 sensor can represent 10:1 to 18:1, but a narrow band O2 sensor can't.

              Dean
              When I said Moronic it is just the nickname I have given it.

              I was talking about the resolution of a narrowband O2 signal off of stoich.

              With the LENZ standalone EMS that I have on the car it only uses a NBO2 at the moment for the closed loop control. The wideband is almost completed. Anyway, I also have an FJO wideband (without a sim NB option) on the car completely seperate from the LENZ.

              The FJO wideband was the first "mod" I ever bought when I got the car. I studied how the Moronic with a JC chip fueled the car during all situations. There are some "scary" areas.

              Well, the algorithms in the LENZ are unbelievable. With closed loop control (set to control all loads, all RPMs) with only a NBO2 sensor, it is dead on with the WBO2. I can set the target AFR's by giving it the Lambda I want at any load and RPM, and it is VERY accurate. I know that all the documentation to date concurs with the notion that NBO2 sensors are not accurate, but the LENZ has algorithms that can compute the signals and convert accurately.

              T

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