If you have ever ran into this intermittent issue, you know it can be a pain in the brain. You make a wide-open throttle pull and your wideband goes rich, or even lean mid-pull. No matter how much you change your airflow tables, it does the exact same thing, every pull. Don’t immediately expect it’s a wideband problem. Look at your trusty scanner and compare your so-called “bad” wideband to a few other things.
Take a look at this issue below, we see it quite commonly. Mid-pull, the wideband drops out rich. This happened very fast and certainly can’t be a mechanical or tune issue.
What we need to do here is pay some attention to other sensor to see if the wideband is truly bad. Thinking this out, if the wideband AFR sensor went rich, something had to have changed to make it read that. So let's look at the injector pulse width (INJ PW). INJ PW in red is moving up at a smooth almost linear rate. Being this PID is telling us how much fuel is being tossed in the combustion chamber. If the wideband reading was correct, we should see the INJ PW do the exact same movement. Yet, in this case, it does not. So, if INJ PW doesn’t change a crazy amount how does the wideband pick this up?
Second though, do you trust your narrowband oxygen sensors? Let’s be honest, during WOT, they kinda stink. But is there a solid indication of what’s at least happening? Yes, yes, they are! So, let's take the same approach here. If the wideband shows a rich condition mid-pull, why do the narrowband oxygen sensors actually move lean toward the end of the pull?
So now we have two things telling us the wideband just might be incorrect. The INJ PW does not jump crazy, and the narrowband oxygen sensors walk lean, not rich. So, what’s the low down on this problem?
It sure can be a bad Wideband sensor, but more likely the Flute or Wideband Oxygen Sensor sniffing device (Sniffing the AFR out the tail pipe) is not flowing air well. The device traps air and finally the wideband says "I have had enough!"
Try to place the Wideband in the exhaust pipe itself, just as the narrowband oxygen sensors are placed. This alone can help fix this issue. Or, you can get a larger diameter sniffing device.