# Bank 1 runs "lean" after upstream oxygen sensor replacement **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** nissan, pathfinder\ **Created:** [December 11, 2016, 1:38am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060 "2016-12-11T01:38:11Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Rod-Knox](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Rod-Knox](https://community.cartalk.com/u/Rod-Knox)\ **Post date:** [December 11, 2016, 10:52pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/21 "2016-12-11T22:52:51Z")
I would suggest you run a thread chaser in that hole and any others that appear to have issues with the threads. Then install new plugs, clear the memory and take an extended test drive with the scanner reading pertinent data lines. A properly installed plug backing out raises a lot of troubling questions. ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 12, 2016, 1:47am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/22 "2016-12-12T01:47:55Z")
No, spark plugs were not cross-threaded: positive about this I checked all the plugs, and they were all more or less loose, but it is only one which almost fell off spec is 18 ft-lbs… this is way too low in my view: it did not even squash any of the compression o-rings on the plugs this time I made them to go 1/4 turn over spec torque, all 6 of them assembled everything, and… still the same 0.30V so far I have 2 theories: 1 -leak in exhaust before the catalyst 2- bad injector I’m made a leak-test using a shop-vac blowing into an exhaust pipe and soapy water sprayed so far I found one faint leak (slooooowly making bubbles) in the welded seam between the cat and its top flange, then biger (but still not that big) leak down from the cat from the looks of it it is a laughable to throw A/F that much as I see: it would account for the offset when at idle, but not under 2000-3000 RPMS, where gas pressure is substantial so, theory #1 is highly unlikely as to the theory #2… first of all, I’ve never replaced injectors before, but it is likely manageable… how do I identify this to be really a problem, not just shoot in the dark?? ---
**Author:** ![Rod-Knox](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Rod-Knox](https://community.cartalk.com/u/Rod-Knox)\ **Post date:** [December 12, 2016, 2:16am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/23 "2016-12-12T02:16:33Z")
An exhaust leak after the upstream O2 is unlikely to be the culprit here. And while it is possible that an injector is the problem I would imagine that a bad injector would have caused a cylinder missfire code at some point in all your testing. Have you checked manifold vacuum with a mechanical gauge? Is there any indication of poor performance from a single cylinder at any rpm/vehicle speed? Does the car have a history of extended stop and go traffic operation? A coked up valve stem may cause that problem but I have never seen a single valve stem coked on an engine. Of course the problem will always show up somewhere first. ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 12, 2016, 3:21am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/24 "2016-12-12T03:21:19Z")
Engine actually runs very smooth MPG is on the low side (~16) once it started, it was ~18.5 before checking here: [https://www.2carpros.com/articles/how-to-test-a-fuel-injector](https://www.2carpros.com/articles/how-to-test-a-fuel-injector) “A common misconception about cylinder misfires is they cause the engine to run rich, **in the absence of combustion the cylinder contains 14 parts air to 1 part fuel (14:1) which causes a _lean_ condition**.” I’m actually considering it a prime suspect now ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 12, 2016, 3:22am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/25 "2016-12-12T03:22:21Z")
and I have to confess: I used “injector cleaner” fuel additive right before it threw this code, not sure if I clogged one of injectors with dirt ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 12, 2016, 3:28am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/26 "2016-12-12T03:28:57Z")
I think what happens is: - ECU “does not know” if any one cylinder is NOT burning or burning extrelemy lean: it has only one sensor to monitor 3 cylinders - cylinder pumps as much air as it is supposed to, it is not getting any (or low) fuel - A/F ratio is lean for obvious arithmetic here, and obviously it is a reason why it is always 0.30V: because it pumps one cylinder of air with no or low fuel - any leaks on exhaust would show “asymmetric” response to RPM change, but I do not see it, so I have a “leak”, which is proportional to RPMs - to detect misfire: it has to be either detonation present (no such thing for no fuel) or should be no spark (which is not the case either by my testing) ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 12, 2016, 3:44am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/27 "2016-12-12T03:44:01Z")
Answering on other your Qs: I do not know how prior owner ran this car, but he made 150,000 is 10 years and I do have a good highway stretch on it regularly, so “no” on stop&go Car and engine are in great shape: very smooth operation and almost no engine gasses blowback, which is an indicator that low compression is not on top suspects list Did not check manifold vacuum with a gauge, but with a finger seems to be nice&strong ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 13, 2016, 3:55pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/28 "2016-12-13T15:55:56Z")
Update after a lot of new work. I removed and cleaned injectors: all were in good shape, but I’ve cleaned them under pressure with carburetor cleaner, then ultrasonic with water and degreaser, then carb cleaner again. At this point, they all have very consistent spray pattern and can be declared to be in top shape. All the o-rings were replaced, so vacuum would not leak there for sure. To make things even more certain about injectors, I’ve swapped banks 1 and 2 to check if problem follows. Result: CLOSE TO NOTHING Now I have 0.31V reading on Bank 1, instead of 0.30V before. I looked down to the intake ports and valves looked OK, I would probably even classify as CLEAN. At this point I go for compression test on cylinders at bank 1 and then I’m out of idead ☹ ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 13, 2016, 3:59pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/29 "2016-12-13T15:59:50Z")
One more test I did: I used a rug to block exhaust pipe, not create an excessive pressure there (few seconds at a time). Zero correlation with sensor reading on bank 1, not even 1/100 of volt ---
**Author:** ![Rod-Knox](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Rod-Knox](https://community.cartalk.com/u/Rod-Knox)\ **Post date:** [December 13, 2016, 4:33pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/30 "2016-12-13T16:33:51Z")
Do you have access to a lab scope? ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 13, 2016, 5:07pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/31 "2016-12-13T17:07:07Z")
I don’t do not even know what it is. Update on compression: cylinders 1/3/5 are 13.1 / 12.7 / 13.0 - not bad in my view for 150K+ mileage I tried spraying curb-cleaner to the gasket connecting intake manifold (aluminum pie-shaped one, not plastic plenum) to where it meets cylinder head looking to get any revs or at least spikes on sensor: nothing. Still, I’m entertaining an idea about failing gasket between bank 1 heads and this pie-shaped intake manifold. The trouble about it is that bank 1 is where plastic plenum/airbox obstructs all the view. I’ve pretty much pissed that carb cleaner into the dark, hoping for miracle, but I did not probably cover even 30% of potential contact/failure zone ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 13, 2016, 5:13pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/32 "2016-12-13T17:13:49Z")
I was explained by a friend what “lab scope” is, and YES, I can get it ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 13, 2016, 5:31pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/33 "2016-12-13T17:31:12Z")
I can hear some hissing from the top, not from the wheel well gonna look for smog machine or just use propane? ---
**Author:** ![Rod-Knox](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Rod-Knox](https://community.cartalk.com/u/Rod-Knox)\ **Post date:** [December 13, 2016, 5:41pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/34 "2016-12-13T17:41:13Z")
If you hear a hissing you have likley found the problem. ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 13, 2016, 6:18pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/35 "2016-12-13T18:18:36Z")
I hope, sir! 🙂 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. Sure, I was applying some brute force as I was working to loosen nuts on the catalyst, on this side sure enough, but could not imagine it might somehow pop up on the heads-to-intake connection?? ---
**Author:** ![Rod-Knox](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Rod-Knox](https://community.cartalk.com/u/Rod-Knox)\ **Post date:** [December 13, 2016, 6:28pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/36 "2016-12-13T18:28:09Z")
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 not to leak. ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 13, 2016, 9:48pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/37 "2016-12-13T21:48:37Z")
not very reassuring ☹ still, how happened it failed after 150K miles… anyway, will post update once I’m there ---
**Author:** ![Rod-Knox](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Rod-Knox](https://community.cartalk.com/u/Rod-Knox)\ **Post date:** [December 13, 2016, 10:26pm UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/38 "2016-12-13T22:26:12Z")
I thought you had removed and replaced the upper plenum. The seal between the upper and lower sections would be the difficult joint. ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [December 14, 2016, 12:51am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/39 "2016-12-14T00:51:29Z")
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 🙂 I had some smoke through the tail-pipe, but importantly, I have smoke from under the lower intake parts, so diagnosis is official at this point - somehow Ive got a hole there anybody knows if Nissan’s VQ40DE (4.0L V6) has coolant circulating through the lower intake? I managed to avoid draining cooling system so far, as I could take the plenum tilted and shuffled aside doing all other work, so ould we a great surprise to get coolant all around removing aluminum intake header ---
**Author:** ![Rod-Knox](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Rod-Knox](https://community.cartalk.com/u/Rod-Knox)\ **Post date:** [December 14, 2016, 1:00am UTC](https://community.cartalk.com/t/bank-1-runs-lean-after-upstream-oxygen-sensor-replacement/97060/40 "2016-12-14T01:00:27Z")
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