O2 sensor performance with side pipes

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O2 sensor performance with side pipes

Unread postby danielt » Tue Oct 08, 2019 7:32 pm

Just want to confirm this behavior makes sense and not caused by something else.

Factory Five Roadster using BBK 1 5/8" shorty unequal length headers into 2 1/2" J pipe which connects to 4" side pipe. Narrowband O2 sensor is about 5" beyond header flange and Wideband is about 8" beyond that.

From cold start and idle to operating temp (180F Thermostat). Fuel error is 0.96-0.98 at 160-170 IMAF. If I run above idle for a couple of minutes (doing 10 second IMAF steps, or driving on street), idle Fuel error is consistently 1.03-1.05. If I let idle for a long time (10-15minutes), the fuel error will steadily decay down to 0.96-0.98.

My assumption is this is from the O2 cooling off.

The wideband tends to go the opposite direction. In long idles, it reads 15-22:1. With a little bit of RPM, it is rock steady at 13.5-14.5. It will stay in that range for a little bit of time after returning to idle, but after 1-2 minutes, it goes back to reading extremely lean.

My assumptions:
Narrowband reading slightly rich when they cool off. Is this normal behavior?
Wideband is getting some fresh air reversion either from the J-pipe to exhaust flange or just too close to the large sewer pipes causing it to read lean at very load flow.
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Re: O2 sensor performance with side pipes

Unread postby decipha » Tue Oct 08, 2019 8:03 pm

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