Lambda Sensor Output at Idle

[lemonslap]

Hi All,

Vehicle: Suburu Legacy 3.0 H6, has an idle issue. When viewing the Lambda sensors output, nothing is logged at idle until increase revs above 1000rpm then they kick into life?
Any one seen this before?

Many thanks

[ch427]

have you looked at the data when the engine was hot or cold?
Generally lambda sensors dont switch correctly until they have warmed up

[lemonslap]

yes closed loop, weird problem idle lumpy some times stalls. Don't think there is an air leak as the fuel trim is fine (about 2%) on both banks.

[stevieturbo]

When you say nothing is logged...what do you mean ?

Exactly how are you reading the sensor info ?

But if all is well they should be operating/switching correctly at idle speed

Edited by stevieturbo on Monday 6th May 11:32

[lemonslap]

Thanks Stevie

I am using Gendan EngineCheck Pro on a laptop, sorry wasn't clear before the output seems to be stuck at the lean setting at idle.

[stevieturbo]

The only proper way to test the lambda sensor is with a scope to monitor it's switching and how fast it is switching.

Data from any OBD type scanner would be too slow. Although if it is stuck reading a low or high voltage it would indicate a problem.

[lemonslap]

These are my findings:

Bank 1 at idle (constant lean):



Bank 1 at 1100rpm:



Bank 2 at idle:



Bank 2 at 1100rpm:



Thanks for your help Stevie

PS sorry for the poor pictures

[Sardonicus]

If your the O2 sensor/s is locking out lean then have you checked for air leaks? might be worth getting a Vacuum gauge on the motor to see whats occurring have a look at those little Vacuum tubes/hoses that the Japs like using by the hundreds for splits or perishing.

[lemonslap]

But wouldn't the fuel trim be high on the affected bank? both banks are showing 2.5% max

[N7GTX]

What are the downstream sensors reading on a hot engine idling? Are they fixed at around 0.6v (normal) or are they stuck at either 0.1v (very lean) or 0.8v (too rich)?
Short term fuel trims (STFT) should be around zero but moving + or - to max of 5 ideally.

[lemonslap]

thanks N7, I will post later but the post cat sensors output was fine. I have ordered two new pre cat sensors today as I need to rule them out. For info there are no fault codes stored just a poor idle and a rare stall event.

[lemonslap]

Just to update everyone, replaced both the Lambda's and the problem has gone. I fitted Subaru OEM ones in the end after a well known car parts provider sent me used sensors!(which they now they won't take back )