You need more than just one reading to assess the fuel system. If all is copacetic the upstream O2's will bounce around zero and read in the microamp range rather than milliamp. But it will always go back and forth, positive then negative. The 2 milliamp figure for bank one is telling you something is going on there, that's too high. Positive current reading equals a lean indication, that's the opposite of the earlier sensors where a high VOLTAGE meant rich indication. So, you need to watch the upstreams and see if it stays high current like that or toggles back and forth. Likewise, see what the other side is doing and it will help you decide if the trouble is global or mostly on one bank.

Good luck!

 

S2 readings are only for determining catalyst performance - period. Amperages are the amount of current the heater in the sensor is drawing - nothing to do with fuel trims. Heaters are built into O2 sensors to warm them up and allow the engine to attain closed-loop status more quickly.

Before you look at O2 sensors you'll need to warm the sensors up by running the engine @ 2,000 rpm for a couple minutes then allow it to return to idle. What you want to observe first is the long-term fuel trim to see how much fuel is being added/subtracted (between -10 & +10 is considered acceptable, beyond that will trigger codes) then look at B1S1 & B2S1 O2 voltages, preferably in graphing mode, if available. Sensor outputs should report a sine wave type fluctuation with voltages running between ~.1 and ~.8 volts. O2 sensor range is 0-.9v with .45v being the 'threshold' voltage which represents neither rich nor lean. Above threshold represents rich, below threshold represents lean. Good sensors will report approx. 10 transitions/sec across threshold, 'lazy' sensors less than 8.

To put this to good use is to employ 'artificial enrichment' while observing the voltages. While watching, again graphing is preferred, spray a flammable product, such as carb or brake clean or use an unlit propane torch with hose attached to tip, around suspect areas that would allow unmetered air into the engine - vacuum hoses, intake manifold gaskets, intake snorkel (after the MAF sensor), etc. A leak will be detected when you observe an O2 sensor suddenly spike upwards to .9v and hold there longer than normal (or as long as you continue to spray into the leak.) BE CAREFUL! Keep a fire extinguisher handy, do not spray into/onto coil packs, hot exhaust manifolds, etc. You don't want to set the car or yourself or your garage on fire!

 

Beav,

Please be sure you are clear on the engine systems when offering advice. The op's car is a 1999 XK8 which has a different engine management system than your 1998. His AJ27 uses different Oxygen Sensors that yours, and they are monitored by CURRENT, and that IS NOT the current drawn by the heater. There is no VOLTAGE to monitor on the AJ27 upstream sensor, it is a current signal. See the attached document. As far as the downstream sensors being for catalyst monitoring PERIOD, that is no longer true either. The current Denso systems also use the downstream signal for additional fine tuning of the fuel metering in addition to catalyst monitoring.

We need to try to be as accurate as we can since there are many variances between model years. It is way too easy to mislead, so we need to be careful.

Cheers,

 

you are going to have to put that car on a 5 gas analyzer and do a cylinder compression test. you need a better scanner that can look at live data on the o2sensors. so you can gun the throttle and see if the switch or not. If so; the 02 sensors are working. that problem could be internal engine always cover basics first

 

I stand corrected, you are right, I didn't realize the model year.

 

Done and running...but another code has shown it ugly head just to keep me on my toes.
I replaced both upstream O2 sensors with Bosch bought from Amazone for $ 117.00 (what a difference from the original Denso sold by dealers for $ 400+!!). I drove the car for 1500 miles from PA to NC and back , averaging 25.6 mpg while cruising with a top down around 70mph. Better gas mileage than my Volvo V70. Anyway, after driving about 250 miles a "check engine" came on. Fortunately, no "restricted performance" . Code P0455. I erased it, not wanting to deal with it on the road, but after another 180 miles it came back again. It seems, it kicks in in a heavy or city traffic. Looking through forums I learned that a purge valve is the most likely culprit. But I cannot find it (1999 XK8 convertible). Where it is supposed to be mounted is only a black metal mount. I wonder whether there are some variations of the valve location, or if the previous owners modified the set-up?

 

so, O2 sensor was giving bad info to the ECM? all trims reading evenly now?

 

strangely so, trims are almost equal. Must be good enough for not triggering "restricted performance". P0455 seems to be unrelated to the previous problem.

 

I agree, its separate.hey, its some good news at least, proceed.