tldr; How far back in the exhaust can I place a wideband and still have accurate readings?


So I bought a ridiculously cheap miata with an FMII kit on it. It currently has no instrumentation and I'd like to get a baseline before I rip out the Bpipes and replace it with MS. Currently the bung in the downpipe is presumably feeding the piggyback, but there is a secondary bung located roughly in front of the driver's seat. Would that be an acceptable location if I'm just running it to a gauge in the car?

 

I made a tailpipe sniffer using a 2.5" to 3" coupler, about 2ft long past the sensor. It fits tight into a 3" exhaust pipe, seals up almost without any leaks at all. It will read within 0.5 AFR of a completely different wideband mounted further up the exhaust. I am sure the response time is worse at lower RPMs, but it works for tuning startup when the main wideband doesn't start up in time.

I say go for it.

 

The tailpipe probes are pretty common at dyno shops, so locating it in the trans tunnel is no concern. Maybe a couple seconds longer sensor warmup time during a cold start, than if it was mounted in the downpipe close to the turbo.

 

Awesome, that's what I figured. Thanks gang.

 

In the midpipe is fine.

Mine's in the back end of the extractors, I think just past the bellhousing from memory.
I think that's about where Innovate said to put it (cant remember how many cm from the valves they said)

regardless, it's always shown normal readings, and matches what i'd expect from the factory ECU (yeah, i have a strange setup)