Subaru WRX Front O2 sensor relocation (twin scroll)

Hello everyone,

Have anyone done a twin scroll turbo conversion on a USDM WRX? Have you relocated the front O2 sensor in the downpipe post turbo?

We did that to a friend’s 2011 WRX and there seems to have a delay in the front O2 reading that makes the AF Correction act crazy, and overshooting the lambda target a lot in close loop, going to -20 to +20. We’re gonna replace the sensor tomorrow just in case it’s slow to respond, but I’m curious if it happened to somebody else.

We are tuning with Cobb Accesstuner.

Thanks!

Frank

Update : we replaced the O2 sensor and the readings are as they should be, everything is back to normal!

Going back on the dyno!

Frank,

The transfer delay does often play havoc on the closed loop fuel system when relocated that much further from the engine.

The ability to adjust transport delay is not present.

Sticking it near the stock location is a common solution, with the understanding it's just seeing one scroll.

If you have tiny primary, secondary runners and idle up, sometimes the behavior isn't bad because exhaust flow is relatively quick, and time from combustion to the sensor isn't so disparate from stock.

Hey Mike,

Thanks for the reply! Since we replace the sensor, the oscillations are now under control. What made me think it was a bad sensor is that even in steady state at 2500 the closeloop system was triming from min to max and the car was basically undriveable. Last year he was running the same turbo setup with the O2 at the same location without issues.

I can still see some very small variance at idle (more than usual) but I can't consider it an issue.

Awesome. Yup once exhaust velocity is high enough, it doesn't seem to present much of an issue.