[ike84]

Blue -

How does a Pin Hole at the bung weld influence O2 sensor readings?
First think about "your own" experiences with exhaust leaks. Large ones!!
They make a sound (a pulsing sound) so that positive pressure you refer to is not constant. It pulses. (A light should have just turned on in your head)
So "Any" type of exhaust leak ahead of or at the O2 sensor allows oxygen into the exhaust stream and the O2 sensor sees it.
Exhaust leaks especially pinhole leaks at bung welds and all welds in the exhaust system are grossly overlooked when attempting to diagnose lean conditions. They are probably the most over looked cause of a lean condition.
Not just by guys like you and I but dealers,shop, everyone.
Also pinhole leaks in welds are damn hard to find.

Common lean conditions as caused by Intake Vacuum leaks are actually simple to diagnose. The methods I described for you seldom fail if done correctly.
But when people have lean conditions caused by exhaust leaks (especially small ones) or failing or biased sensors (other then the MAF) they get stuck. The are convinced they have a intake vacuum leak.

Another thing I think happens is a mental block.
Most people think of lean conditions in terms Fuel/Air ratio.
When they think of exhaust they think in terms of that fuel/Air ratio after combustion. Few people consider the possibility of ....Exhaust/Air..... ratios changing "after" combustion.

Hope this sheds some light on pinhole exhaust leaks and there relationship to The O2 sensor

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