Hi John,

As you said, the standard O2 sensor (narrowband sensor) can only tell if the AFR is richer or leaner than 14.7:1....it doesnt know how much richer or leaner. so disregard the readings your meter readings you are getting.

If your fuel economy is getting worse, this is usually a sign that your O2 sensor is on its way out. O2 sensors start to read 'lean' when they fail, so will then pump more fuel into the engine - hence the worse economy.

i believe most O2 sensors only last 50,000kms, when was the last time you changed yours?


one more thing to check, is your possumlink in a closed or open loop lamda?
if its open loop, the O2 sensor wont be doing anything. so you might have a problem elsewhere.

cheers, Steve

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MY99 - 245hp & 360Nm.......Best ET - 12.771s