Any disadvantages of using an 02 sensor spacer?

[Mr_Bob]

Hi Guys,

I've got a TBE on the way, but haven't decided who i will use for a tune yet,
In the meanwhile I'm considering dropping an 02 spacer in.
I'm also thinking that the spacer will allow me to reflash back to stock for future servicing, so the DP doesn't cause a CEL.

From what i understand, the 02 sensor is used for the ECU calculations for fuel.
I've also heard that the 02 sensor must reach a fairly high temp before it operates properly
This makes me think that adding the spacer will affect the performance of the car by giving faulty readings, does anyone know if this is the case?

(I'm not expecting improved performance from the TBE until I get the tune)

[Greg Roles]

I think there are two O2 sensors on the petrol cars, one post turbo for fuelling, and one post cat for just the cat?

I was under the impression you only needed to space the second sensor, to allow for the higher flow aftermarket cat, and the fuelling one remains as is. Could be wrong.....

[noone]

That was my understanding. I also was led to believe it was not used much for adaptation, but to detect an issue.

[h100vw]

Only a snag on race cats usually, from experience. 200cell and upwards don't seem to be an issue.

Most Stage/Phase 2 tunes prevent CELs coming up anyway.

Gavin

[Tim]

Ive sold plenty of spacers to people looking to reduce cat efficiency errors. They are for use on the post (after) cat sensor ONLY! This sensor just checks your emissions and raises an alarm if it thinks your cat is not doing its job properly.

[Mr_Bob]

Thanks guys,
TBH i wasn't aware that there were 2 sensors.
This makes alot of sense, looks like i'm in the market for an 02 Sensor spacer

[mk3pete]

what would happen if you were to put it on the before cat sensor?

[noone]

it would misread flows, not what is was designed for.

[mk3pete]

indeed but am more interested in exactly what it would do to the car.

[Greg Roles]

My best guess is it would make the car run very lean, as for a given flow of air as measured by the intake MAF, the ECU would be reading lower post turbo O2 levels due to it being removed from the direct exhaust flow. Lack of exhaust oxygen is a fuel rich situation, so the ECU would pull fuel to try and bring the exhaust O2 back to expected levels. The engine would run too lean.

If this is true, it would be terminal to you petrol types, only diesels can hack that sort of thing.