Accuracy of SP WBO2 sensor?


New Member
May 27, 2001
Had my truck on the dyno for the first time last week, and it was an interesting experience, one that has given me a few things to sort out.

One unexpected question that came up was the accuracy of the SpeedPro's WBO2 sensor. The SP sensor did not agree with the WBO2 the dyno operator was using, with the SP sensor generally reading 5% richer than the shop's sensor (e.g., the shop's tailpipe-sniffing WBO2 would read 12.2, while the SP would read 11.6). FWIW, I am confident that I don't have any leaks in the exhaust between the WBO2 and the tailpipe, as the system does not have any flanged joints in that that section, and that section has recently been replaced with with new pipe. So let's assume that the problem is not related to an exhaust leak.

Is this sort of discrepency common? While I realize it could be the shop's sensor that's inaccurate, is there any way to verify the accuracy of my sensor short of sending it in? I'm starting to tune this engine in earnest, and i want to make sure I can trust the WBO2.


There are so many issues with making statements relative to WB O2s, that I just say these are what I've found to be true.

First and formost people that tune to get a particular AFR aren't tuning, they are just looking for numbers.

On my own GN using a true DIY WB I run best at 11.6:1. But that is in car, and on the road.

Unless you doing lab grade work there will be errors within any amateur setup. Maybe megabucks, but less then lab grade and your just approximating.

I'd just lean to the sensor with the fewer hours as **Possibly** being the most accurate of the 2.

To run an engine with a WB, and not have it powered up will due serious harn to the sensor (NTK Types, not sure on others)

Tune for best power, use the WB just as a tuning tool. Record what your best HP is at. Don't tune to get a specific AFR.

Not harping at you, just some statements to help all
Thanks. I appreciate what you're saying, and I do understand the inaccuracies inherent in any tool taken outside of a labratory setting, and I understand that max power is the goal. I'm new to tuning with a WBO2, so I'm just trying to get a handle on which numbers I can trust.

Originally posted by bruce
On my own GN using a true DIY WB I run best at 11.6:1. But that is in car, and on the road.

um.....did you make your own WB O2?

just curious

what do you mean by "truw DIY WB?"

I use my speed pro wb o2 just as a tuning aid and not for absoulute numbers.I talked to Harry about this and he said to adjust your target AR a little at a time one way and then the other and see witch way the car picks up. The number are just to be used as a bench mark and not true AR