no o2 sensor cause lean conditon

[bastianshaw]

I want to ask a bout motronic and o2 sensors it seems to me if the ecu doesnt get a signal it defaults to a rich condition yea?

would a car ever run LEAN from no o2?

[FLG]

Yes it will run a conservative rich tune.

Also this is assuming there are no issue with other sensors/intake leaks.

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[nando]

it doesn't default to a "rich" tune. all it does is disable O2 feedback long term and short term trims.

there's no such thing as a default "rich" tune in the first place - common internet myth. The default tune is just the tune made for the stock engine as it left the factory before feedback loops are added in.

it could definitely run lean without the O2 if something was causing the O2 feedback to increase fuel trims to make up for a lean condition.

just keep your working O2 sensor (or replace it). there's zero reason to remove it.

[FLG]

Nando, wouldn't though the tune be on the rich side of things? Assuming everything else is in order.

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[nando]

no. it's just a default tune for a stock motor. when everything is new you want the lambda corrections to be 1.0. if it defaulted rich, you'd have to rely on the lambda feedback to dial it back constantly - this is not good tuning strategy and it would have problems with emissions.

[FLG]

Gotcha. Sorry for the misinformation.

Learned something new.

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[nando]

no biggie, it's something that's been repeated over and over again for years - but it's not true. no such "rich" fuel map exists. it's just the standard map, except fuel trims will not work (obviously) without O2 feedback. and there's no reason to disable that..

[bastianshaw]

it doesn't default to a "rich" tune. all it does is disable O2 feedback long term and short term trims.

there's no such thing as a default "rich" tune in the first place - common internet myth. The default tune is just the tune made for the stock engine as it left the factory before feedback loops are added in.

it could definitely run lean without the O2 if something was causing the O2 feedback to increase fuel trims to make up for a lean condition.

just keep your working O2 sensor (or replace it). there's zero reason to remove it.

woukd a faulty o2 relay do this?

[nando]

a bad O2 heater relay will generally turn O2 feedback off, yes.

[AndrewBird]

I thought that if the ECU didn't receive a signal, it used fuel maps for sea level elevation, being that you would never need a richer fuel mix, so everything was covered. If you aren't at sea level, then the car would run rich.

[nando]

Motronic 1.3 has no way to know what your elevation is. there's no differentiation between altitudes and maps either - it only really has 2 fuel maps, one for part throttle and one for WOT. no limp modes or anything.