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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / June 2005Help interpreting oxygen sensor data
Hi, After seeing a decrease in mileage on my 96 Ford Taurus wagon (~ 24 to ~20 mpg. 140.000 Mi odo), I decided to take a look at my oxygen sensors as a possible culprit. I read out their voltages during idle when warm using my Elm ODB scantool, and plotted them. http://www.duijn.info/OxygenSensor.jpg x in seconds, y in volts It looks to me that something is fishy in Bank 2, but the signal does not look like the typical error modes that I read about (sluggish, low, flat). Bank 1 looks like the examples I saw for good sensors. I am not experienced enough to make a statement on these curves, but am hoping they ring a bell with one of you people. Does it look familar, is my data aquisistion simply too slow (I don't have a scope, sorry...). The peaks in sensor 2/2 also look like they don't belong there. Is the fuel injection acting up due to bad info from sensor 1, and too rich a mixture making its way through the cat? The traces were recorded separately to improve time resolution... If a sensor is indeed bad, is it doable to replace it with just basic tools, or is it best left to a pro? Thanks for any thoughts you may have. Martijn > Hi, > [quoted text clipped - 25 lines] > > Martijn 1/1 appears to be fine. 1/2 should have a relatively flat output though which appears to indicate that the catalytic converter on that bank isn't doing much. 2/1 is either dead or genuinely indicating a very weak mixture. However if the mixture really was very weak then 2/2 wouldn't be displaying higher readings so it appears that 2/1 really is dead. Until you replace 2/1 there's little point in trying to decide if that converter or 2/2 are ok or not. Sensors just unscrew so if you can handle a spanner I very much doubt you need a 'pro' to do it for you. -- Dave Baker - Puma Race Engines (www.pumaracing.co.uk) > > I read out their voltages during idle when warm using my Elm ODB > > scantool, and plotted them. > > > > http://www.duijn.info/OxygenSensor.jpg > > x in seconds, y in volts > 1/1 appears to be fine. 1/2 should have a relatively flat output though > which appears to indicate that the catalytic converter on that bank isn't > doing much. 1/2 is pretty flat... (it's below 1/1, not beside it). Of course, that's assuming Martin labelled the charts correctly. :) > 2/1 is either dead or genuinely indicating a very weak mixture. However if > the mixture really was very weak then 2/2 wouldn't be displaying higher > readings so it appears that 2/1 really is dead. Until you replace 2/1 > there's little point in trying to decide if that converter or 2/2 are ok or > not. 2/1 (top right) is all over the place, with 2/2 (bottom right) following close behind. Sticky/plugged injector, misfiring plug, bad wire, vacuum leak? > Sensors just unscrew so if you can handle a spanner I very much doubt you > need a 'pro' to do it for you. Yup. > > > I read out their voltages during idle when warm using my Elm ODB > > > scantool, and plotted them. [quoted text clipped - 8 lines] > 1/2 is pretty flat... (it's below 1/1, not beside it). > Of course, that's assuming Martin labelled the charts correctly. :) If bank 1 catalytic convertor was storing oxygen properly, what would/should B1S1 be doing? > > 2/1 is either dead or genuinely indicating a very weak mixture. However if > > the mixture really was very weak then 2/2 wouldn't be displaying higher [quoted text clipped - 6 lines] > > Sticky/plugged injector, misfiring plug, bad wire, vacuum leak? Yup, something is amiss. > > Sensors just unscrew so if you can handle a spanner I very much doubt you > > need a 'pro' to do it for you. > > Yup. The OP would be wise to scrutinize the fuel trims. >>>>I read out their voltages during idle when warm using my Elm ODB >>>>scantool, and plotted them. [quoted text clipped - 33 lines] > > The OP would be wise to scrutinize the fuel trims. When I recorded the traces, both long terms were -1, short terms fluctuating a bit between 3 and 9. Martijn > > > I read out their voltages during idle when warm using my Elm ODB > > > scantool, and plotted them. [quoted text clipped - 8 lines] > 1/2 is pretty flat... (it's below 1/1, not beside it). > Of course, that's assuming Martin labelled the charts correctly. :) Oops. You're quite right. I read the chart incorrectly. Bank 1 is fine. Bank 2 clearly isn't. A first step might be to swap sensors 1/1 and 2/1 and see if the rich readings shown by the second sensor move with the first sensor or stay on bank 2. If they move to bank 1 then sensor 2/1 (now on bank 1 of course) needs replacing before anything else can be checked. -- Dave Baker - Puma Race Engines (www.pumaracing.co.uk) >>>I read out their voltages during idle when warm using my Elm ODB >>>scantool, and plotted them. [quoted text clipped - 21 lines] > > Sticky/plugged injector, misfiring plug, bad wire, vacuum leak? Would you guess on of the above are more likely than the sensor itself being bad? Easy enough to swap 1 and 2 and try, judging from the other posts. Platinum plugs and wires are 20.000 miles old, I'd be a bit surprised if they were bad. Wouldn't vacuum leaks affect both banks equally? Injector? Perhaps... The engine seems to run OK though. I can try a cleaner at some point. Thanks for the comments Martijn > > >>Sensors just unscrew so if you can handle a spanner I very much doubt you >>need a 'pro' to do it for you. > > Yup. > Would you guess on of the above are more likely than the sensor itself > being bad? [quoted text clipped - 3 lines] > Injector? Perhaps... The engine seems to run OK though. I can try a > cleaner at some point. The highly active bank 2 sensor would typically indicate a poor catalyst on that bank, or an exaust that hasn't reached temperature yet (not likely since the other side is OK). The bank 1 sensor on that side shows a less than ideal trace, so you could simply be overloading that catalyst with excess fuel or air. Since you are using your OBD data stream to create a graph, your result is a low resolution and inaccurate (in terms of real time) chart. Note the random pattern of plot points compared to B1S1. Anyway, look for something that would cause a mixture issue with one bank, like pluged EGR ports in the intake, leaking vacuum hose(s) exiting from a specific runner of the intake, bad injector, wire, etc. Do you have any cylinder misfire codes? Can your scanner read live misfire data engine running? Toyota MDT in MO >>Would you guess on of the above are more likely than the sensor itself >>being bad? [quoted text clipped - 12 lines] > inaccurate (in terms of real time) chart. Note the random pattern of > plot points compared to B1S1. Yeah, I noted the erratic curve, my sampling rate is just insufficient indeed. But I assumed it would normally be similar to bank 1. I am hoping that excess fuel overloads the cat (would be consistent with poor mileage), not particularly looking forward to getting a cat replacement. > Anyway, look for something that would cause a mixture issue with one > bank, like pluged EGR ports in the intake, leaking vacuum hose(s) > exiting from a specific runner of the intake, bad injector, wire, etc. > Do you have any cylinder misfire codes? Can your scanner read live > misfire data engine running? I'll give it a try this weekend. I'll start by swapping sensors, an trace the other options as far as I am able to. No misfire codes, I will have to check on 'live' misfire options. I have had an EGR code come up (excessive flow detected), but the code comes randomly and either goes away after 3 drive cycles or I reset it sooner than that. As the engine runs fine, I blamed the code to a flaky DPFE sensor that I couldn't be bothered to replace. I think the EGR is common to both banks though, but not 100% sure on that. No codes active at this time though. Martijn > Toyota MDT in MO > Platinum plugs and wires are 20.000 miles old, I'd be a bit surprised if > they were bad. Wouldn't vacuum leaks affect both banks equally? [quoted text clipped - 4 lines] > > Martijn The highly active bank 2 rear sensor would typically indicate a poor catalyst on that bank, or an exaust that hasn't reached temperature yet (not likely since the other side is OK). The bank 1 sensor on that side shows a less than ideal trace, so you could simply be overloading that catalyst with the incorrect amount of fuel or air. Since you are using your OBD data stream to create a graph, your result is a low resolution and inaccurate (in terms of real time) chart. Note the random pattern of plot points compared to B1S1. Anyway, look for something that would cause a mixture issue with one bank, like pluged EGR ports in the intake, leaking vacuum hose(s) exiting from a specific runner of the intake, bad injector, wire, etc. Do you have any cylinder misfire codes? Can your scanner read live misfire data engine running? Toyota MDT in MO |
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