This is 4.0L V6 Nissan Pathfinder. Originally it threw P0420 code, which is “Bank 1 Catalyst efficiency below normal”, so I replaced catalyst on Bank 1. Next it threw PA200, which is for faulty upstream oxygen sensor on Bank 1. I measured what old sensor was showing, and it was running in narrow …

I can hear some hissing from the top, not from the wheel well gonna look for smog machine or just use propane?

If you hear a hissing you have likley found the problem.

I hope, sir! :slight_smile: Unfortunately I could not confirm it with a carb-cleaner spray, just to be sure. Gasket set is not very expensive, and by this point I can get all the top removed and reinstalled with closed eyes. I wonder WHY it would leak? Connected worry is if anything was cracked. …

Intake manifolds are prone to mate unevenly. There are various techniques to get the manifold to nestle into position evenly and only with close attention or a great deal of luck can the mating be successful. Even the small block Chevy intakes took some care to get settled squarely in place so as no…

not very reassuring :frowning: still, how happened it failed after 150K miles… anyway, will post update once I’m there

I used “crazy Russian” method to make a smoke machine on a dime: plastic bottle hot-glued piece of hose to the cap hot-glue compressor trigger-handle to the bottom cigarette into the cap’s hole lit it up and blow :slight_smile: I had some smoke through the tail-pipe, but importantly, I have smok…

Who was it that said “the harder I work the luckier I get?”

I do not know, man, but I do really appreciate your and all others ideas and advice!

Please define “smoke from under the lower intake parts” Do you mean smoke is coming out, from under the intake gaskets? That would mean the intake gaskets themselves aren’t sealing . . . I thought you had replaced them? Do you mean the manifold itself is leaking?

Bank 1 runs "lean" after upstream oxygen sensor replacement

Maintenance/Repairs

Rod-Knox December 13, 2016, 10:26pm 38

I thought you had removed and replaced the upper plenum. The seal between the upper and lower sections would be the difficult joint.

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Bank 1 runs "lean" after upstream oxygen sensor replacement

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