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O2 sensor values-constantly lean

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  • O2 sensor values-constantly lean

    So when putting this car together I replaced everything I could including oxygen sensor. I've put LPG injection on it, AC Stag 300 ISA2 to be exact.

    Anyway, I updated the software and ran the auto calibration and it kept popping up with setting the lambda value or run auto calibration again. I can check the lambda values (O2 sensor output) on the software and its constantly around 0.19 at idle. Gunning it doesn't change it much. It was sitting at this same level before the update of LPG ECU (not important to the question, just pre-empting).

    Anyway, thought I would check things a bit more this morning. Car was at operating temperature so O2 sensor was well and truly at operating temp. On removing a vacuum hose to lean things out the value dropped to 0.00. Squirting hydrocarbons into vacuum port in manifold the value rose to 0.6 at one stage, but that was the highest it got and it was well and truly rich as I stalled it.

    To me these figures seem low, although I'm not overly experienced with O2 sensor outputs. Based on my reading I was expecting lowest value to be 0.1v when lean and when rich it should rise all the way up to 0.9v.

    Car is 99 NL 3.5l. Car seems to be running fine. Fuel use since rego a few weeks ago has been about 15l/100km on petrol, and 17.5l/100km on LPG, both a mixture of urban and country about half half. Driving like a nana I thought it would be a bit lower on petrol at least.

    Does this sound like my O2 sensor is off and not reading correctly?


  • #2
    And checking other wiring diagrams, mine is different. On car loom I've got white red, blue red, blue yellow, and blue something (black?)

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    • #3
      So I found the old sensor with plug cut off, and jammed the wires into connector. This one is acting completely different-constantly jumping from lean to rich at idle as I understand they're supposed to.

      Attached photo shows the oscilloscope line in purple of the new O2 sensor. The previous sensor was just a constant line at at 0.12v, this one goes up and down as you can see

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      • #4
        Well, I thought I would try one of the O2 sensors I recently pulled out of the Camry, where the new ones didn't fix the miss and rough running so I assumed they were alright (had to mod the connector). Seemed to be giving right signal (if that oscilloscope image is the right sort of signal, no responses here so I'm still not sure).

        On lpg the car seems to surging a bit, like the mixture is bouncing around until it finally settles if the car stays at that rev range, which isn't often. Doesn't seem to do it on petrol. It didn't do this before with the original replacement sensor that was only giving 0.18 at idle

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        • #5
          I cannot find anything relating to the 3.5 L engine and its oxygen sensor, but looking at my Max Elery W/S manual, it gives some figures for the 3.8 L engine so they may ne relevant to the earlier 3.5 engines. This gives values for the front sensor - while warming up the engine as" High RPM then release accelerator", 200 mV or less. "Race Engine" - 600 -1000 mV, "Idling engine" voltage 400 mV or less, and "Engine 2500 R/Min" 600 - 1000 mV. It simply gives readings for a warmed up engine from the REAR sensor as 0 to 600 - 1000mV while racing the engine.

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          • #6
            Awesome, thanks erad. That's more info than I've been able to find with a lot of reading

            What exactly does "race engine" mean?

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            • #7
              Also, I'm guessing those figures should be correct as all oxygen sensors behave the same (assuming the same type)

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              • #8
                Stu:

                Your guess is as good as mine when you ask what '"Race Engine" means. I reckon it is simply rev it hard - maybe 3000 R/min. I quoted the text in parenthis because I wasn't sure of what it meant either. My interpretation is that if the reading is low, the mixtures are fairly close to what they should be ie not too rich. I imagine if you had zero, maybe it would be too lean though. What the cutoff should be - who knows?

                I had a quick look at Google on this subject and I quote a bot from what I found below:



                You can test the oxygen sensor at home with a voltmeter or OBD2 scan tool like the FIXD Sensor. Go to the live data feed within the FIXD app to see the voltage and response time of your O2 sensors.

                Typically, a front (upstream) O2 sensor 1 that is functioning properly will be switching from rich to lean at a fairly steady rate, creating a wavelike formation. The voltage generated from the O2 sensor should be from 0.1V to 0.9V, with 0.9V on the rich side and 0.1V on the lean side. If your readings are within this range, the O2 sensor is functioning properly.

                The rear (downstream) oxygen sensor 2 is a catalyst monitor and if everything is operating normally, this sensor will be hovering around half a volt. However, this measurement can fluctuate depending on the manufacturer.


                Additional O2 Sensor Testing Tips


                If the O2 Sensor is not responding quickly to testing:

                If the sensor seems sluggish or slow to respond during testing and there are other symptoms without a fault code, this may be an issue of a “lazy” O2 sensor that can cause other problems.

                If the O2 Sensor voltage is sticking rich or lean:

                Try introducing the opposite condition to determine if the issue is with the oxygen sensor or if it’s an air-fuel mixture issue. For example, if your O2 sensor is sticking lean, add fuel to the situation to see if it responds. If the O2 sensor is on the rich side, try introducing a vacuum leak or more oxygen to see how and if the sensor responds.
                Last edited by erad; 1 week ago.

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                • #9
                  Thanks Erad. It's funny that the sensor currently in it gives that wave like pattern, but it sits there hunting around when load changes on it (going up a steady hill, or coming to stop and idling). The sensor I thought was bad didn't do that, was nice and steady at all loads.

                  Going to put that sensor back in and try it all again, compare to the values you gave.

                  Thanks again for the help

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                  • #10
                    Finally figured out why wiring colors are different on mine. Getting to the original plug for O2 sensor was a 2-3 hr experience, probably more. Tucked up beside the gearbox where you can't get to it to unplug it. Really frustrating is putting it mildly. I made an extension to put the plug in an easily accessible location further down, which has made it a 5 min experience to change when working slowly

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