FAST Dual Wideband Crazy, or am I?
 

After the 706 heads on my 5.3 went TU, i went with some 243's and since they flow a bit more... my tune is off. I already strapped it to dyno to check tune and afr was 12.3.

I put a slightly bigger pulley on to make the tune less off until i am able to get her tuned. But for now i welded in two O2 bungs and borrowed my uncles FAST dual wideband... just to see where i was at.

This thing is driving me CRAZY :confused: During a street pull, 2nd gear, sometimes bank 1 reads 12.3 and 2 reads 10.8. Then i check it again after work and it's the other way 1 is 10.8 and bank 2 is 12.3. What the hell is going on?

This FAST box warms the sensors before you start the vehicle and has had very little use. Could the box be bad? Bad sensor? I just don't know. I got so frustrated with the wideband i took it off and put the exhaust plugs back in. I guess i will drive her easy until i get the tune.

Possible exhaust leaks? Also might want to double check the grounds.

Swap the O2's and see if the low reading follows it.

The low will jump to the other side on its own... read my OP. This thing is weird.

There's no leaks... I welded the bungs ahead if the cats. And what grounds? This is a stand alone box. It plugs into cigarette lighter then the sensors.

If you pull the wideband sensors out and leave them free air, do they consistently register 20:1 a/f or larger? If so what does the LTFT and STFT look like?

What is LTFT and STFT?

Long term and short term fuel trims, computers way of correcting fuel irregularities between computer and factory O2 sensors when in closed loop mode. You'll need a scan tool to monitor. Have you checked free air readings of the wideband though?

Yeah, they read 21 in free air. Now what?

So the readings of 10-12 are only in higher throttle/boost, correct? What does the wideband read when doing normal cruising? how far back are the O2 bungs from your header collectors?