Here is everything I've learned while researching the Wideband Oxygen Sensor (WBO2) for the Hydra Nemesis ECU, firmware versions 2.5 - 2.7:
FM sells a replacement oxygen sensor for the Hydra for $250. They sell a cheaper sensor but it's for a different AFR meter and is not compatible with the Hydra. They also sell a sensor with a Hydra "unlock code" for Long Term Trim on the Hydra Nemesis 2.7 firmware for a total cost of $450.
So I called NGK/NTK Tech Support and gave them the following information:
The Flyin' Miata sensor has the following stamped on the body: "LHA:LZA08-H4 NTK JAPAN 6YN6" (the last part is just the manufacturing lot code stamped on the nut). The end of the sensor is a metal can with one hole in the end, and six holes around the circumference. It is a 5-wire sensor with a 6-pin WeatherPack WPT-6 connector which says "2 P.E.D." on the side. The pin-out is:
A = gray (VS reference +)
B = white (IP power +)
C = yellow (heater ground -)
D = black (IP & VS cell ground -)
E = blue (heater power +)
F = no connection
(I looked inside the connector body and there are no jumpers.)
NGK/NTK Tech Support looked it up in their files, and told me:
* This sensor is a NTK stock # 24302 and has a 136ms response time, which is one of the fastest-response units they make.
* The only 'catch' is that in some cases the reseller (Flyin' Miata, in this case) add their own custom connector or jumper, then charge an additional fee for the sensor. This sensor comes from the factory with a connector designed for most Honda / Acura V6 VTEC SOHC engines (3.0 - 3.5L made from 2003-2008).
* This unit is available from most car-parts stores for about $180, but might be special order. (In fact, I called NAPA and they had one in a local warehouse, and got it to me the same day for $150 + tax.)
* 5-wire sensors are designed for maximum accuracy and response times, compared to cheaper 4-wire sensors. They are often labeled "laboratory grade".
* Some 5-wire sensors don't require a free-air calibration because they have some method of auto-calibrating. This sensor is not that fancy; it DOES require a free-air calibration. NTK recommends a minimum of 30-45 minutes of free-air calibration, but longer calibration time is better.
* NTK owns exclusive rights to 5-wire oxygen sensors, but only manufactures about 40% of them, and they contract with Bosch and others to make the rest. (Later I called Bosch tech support and found that their equivalent part number is Bosch 15401.)
* Each sensor model includes a custom ASIC chip to give it proprietary calibration values, so it is not possible to simply swap out a sensor with a sensor from another brand. There are no cross-reference tables like there are for spark plugs.
* Using the wrong sensor can actually fry your ECU. Don't make a very expensive mistake!
* Leaded fuel (some types of racing fuel) will kill the sensor.
* Running rich (like under WOT) can shorten sensor life.
* This particular sensor was designed for GM engines. Although it might last 100,000 miles for that use, two years and 25,000 miles isn't unusual for an aftermarket turbo kit.
* NTK also sells a PowerDex AFX wideband monitoring and datalogging kit for $280, for people who don't have a Hydra ECU (or similar).
* Be cautious about buying sensors online; even if you get exactly the part you expected, warranty service is provided through the reseller, not through NGK/NTK. So you might be out of luck if you have any problems with the sensor.
* Regarding the life of the sensor: NGK/NTK Tech Support said it's hard to say how long these sensors will last; in a OEM application they might last 100,000 miles; but my experience of two years and 25,000 miles seems about right for an aftermarket setup. Several turbo-Miata Hydra owners have told me of similar experiences.
* No NOT use the 24300, it is NOT the same, the internal circuitry is very different.
Also, here are some questions I asked, along with NTK's response:
Q: What does the "-H4" on the part number mean? I ask because I see that your stock # 24302 crosses to an LZA-08-H6 at this website:
A: The -H4 not critical; it's a code stamped for OEM applications (in this case Honda and GM) that tell you the harness length and connector style. (So an -H6 or -HE4 or -HA4 suffix should still use the same sensor body.) The exact definition of the -H4 would need to be answered by a OEM O2 engineer back in the office in Michigan. Most people on the aftermarket are not worried about things like this as they are replacing OEM parts with OEM parts.
Q: I've read some discussions in the forums about whether Hydra needs a sensor with a 3mA or 4mA pump cell. What's the difference, and will the wrong one damage my Hydra or just not sense correctly?
A: The current rating of the pumping cell is directly correlated to the stamping number on the sensor. There is no need to worry about the pumping cell in the sensor body, if the stamping number directly matches our number there is no reason to worry about the amperage of the pumping cell.
Q: I thought you said that Bosch and NTK sensors were made differently and wouldn't cross-reference each other, but the OxygenSensor.net website above says they do. What's going on?
A: NTK and other competitors patent 5 wire sensors, this one may have close similarities, or may actually be the same as one of our sensors as we used this variant in our wideband logging system and supplied the Bosch early in the sale, and switched to supplying the NTK. I would be curious to know where oxygensensor.net got their information. We get ours from our engineering department and this is done in the engineering process with many OEM suppliers, this is the most accurate data you will ever get. The bottom line here is that if the stamping number directly crosses then it’s the same sensor body and internal construction. At this point we just need to verify the wiring on the connector.
Q: You said that each sensor model includes a custom ASIC chip to give it proprietary calibration values, so it is not possible to simply swap out a sensor with a sensor from another brand. There are no cross-reference tables like there are for spark plugs. Is that correct?
A: Yes, the Asic chip is preprogrammed with the calibration values.
NGK Spark Plugs ( USA) Inc.
46929 Magellan Drive
Wixom, MI 48393
I found this tidbit on the NTK website's FAQ's: "Most [oxygen] sensors slowly degrade in performance and send a false rich signal to the ECU, running the engine too lean." That would sure match my symptoms of light pinging under moderate- to heavy-acceleration between 2200-2900 RPM.
It turns out that if you do a Google search for "ntk 24302 hydra" you'll find several threads about replacing the FM sensor with this one. They talk about putting a new connector on the cable from the Hydra, so swapping out sensors becomes an easy plug-n-play solution.
Some other possibly useful pages are below, although the information provided is possibly old or inaccurate:
(Look for klatinn's post near the bottom.)
I've seen some claims that others have successfully used an $80 sensor; that doesn't mean it's accurate or fast enough for all conditions, but maybe it's good enough for most situations. I don't really know.
'99 Mazda Miata
FM-II turbo kit with Hydra Nemesis ECU ver. 2.6.