Guessing I need an O2 sensor

Reprise

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Spent another few minutes with Torque on the blue Sierra and tracked down where the O2 sensor data was shown ("I *know* I've seen it before...where the hell is it again?") :undecided:

Anyway, bank '1' primary is in red; bank '2' is in green. Guessing that I'm going to lose the B1 sensor shortly (no codes yet except a 'pending' P0171; this started as a result of trying to track down intermittent rough idle)

'Good' brands? Bosch, AC Delco, others?

Kind of a virgin at R&R on these; I know there are special sockets available, and they can be a bear to replace. Tips certainly welcomed. Accessibility doesn't look to be an issue, at least.

I'm just going to replace the B1 sensor, unless someone makes a good case for 'both' primaries at once.

The thought just came to mind, as I preview this post...this truck is exempt (!) from emissions testing (meaning that I could someday put in a set of 'long tube' headers, and forgo the O2 sensors entirely - 'tune' them out, as it were -?) Even if that were possible, I still want a quiet exhaust, so as not to be waking my campground neighbours up - been looking at replacements for the Flowmaster that's on it now. And I'm not looking to skip using unleaded gas.

Oh, and I found my Tech2 again yesterday, so will be doing some more in-depth stuff on the Sierra as a result.

Looks like my door switch issues may indeed be with the switch, not a DDM, and that it's sometimes possible to resuscitate them by taking apart & cleaning, vs. just replacing outright. Will be tackling that soon, as I don't want to have the driver's window stuck in the 'down' position (although I suppose I could hook up the handy-dandy Tech2 and 'command' the window back up... 'rise!') 🧙‍♂️

87853
 

Maverick6587

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I'm curious to know what your O2 sensor 2 volts and the short and long-term fuel trims look like. Could you post a screen shot of those as well?
 
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Will do, later today. From memory, the trims looked 'ok'...but I'll capture them & post back.
I know the upstream sensors won't be 'identical' across both banks (my Voy's isn't), but I'm pretty sure this one in my screencap should be more 'wideband' than it is.

Looks like Denso might be in that 'good' brands category, too, from what I see...
 

Mooseman

Moderator
My thoughts on O2 sensors is if one failed, the other isn't far behind. It's like brakes, replace them in pairs.

ACDelco, NTK and Denso have been good to me. I've had a Delphi fail on me once. As for replacement, start soaking them now with a good penetrating oil. Another thing I found was that the actual sensor socket is a bit loose and is a 7/8". I got a metric equivalent deep impact 22mm socket, which is a little more snug on the sensor, cut a slit for the wire and use that now. Less chance of slipping and rounding the hex. Was also cheaper. Sometimes they're so stuck that torch heat is required.
 
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As promised... first, the downstream O2 sensors... and they look similar to the upstream ones...

87859


Next, the fuel trims. I wanted numeric values, but couldn't locate them today, like I did the other day. So they're here on a graph. And for whatever reason, Torque is missing (?) the 'Bank 2 Short Term' item (that's why there are only 7 data points).

And, yes, I only see 5 sets of data myself, although there are 7 in the legend.

On the 'long term' trims, since they're identical (?), the yellow is superimposed on the red (except for the very end of the series).

If you need these separated out into 2-3 plots / graphs, let me know.
And thanks for reviewing. :tiphat:

87860.
 

Maverick6587

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It looks like both sensors on bank 1 are dead. Does bank 1 respond/change when you excellerate/press the gas pedal?

The fuel trims seem really high as well. Probably because of the O2 about giving any data. I think the normal range is between 0 and 9, for fuel trim.
 
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Funny thing is, the ECM is reporting 'too lean'. Actually, when I ran the fault codes today, *both* bank 1 and bank 2 were reporting lean. Bank 1 was still a 'pending', and bank 2 (new) was a 'stored'. But there's still no CEL on the dash. Probably has to be 'x' ignition cycles before the 'stored' one shows up, I'll guess.

Actually, now that I think about it, if they're reporting 'lean', then addn'l fuel would be mixed in. Maybe that's why the trims are higher than you're expecting. Me, I know it's a 6.0L, so I don't even flinch to see 'excessive' fuel consumption on this beast :laugh:

It'll be interesting to see what the plugs look like (especially 1-3-5-7 on the driver's side) when I take them out. If they're black / sooty, we'll know this has been going on for awhile.

I'll have to check whether the bank 1 changes under throttle. But at this point, it looks like I need 2-4 O2 sensors, depending on how much work I want to let myself in for at one time. I'll probably do the two upstream sensors first, then come back for the downstream ones later on. As the conventional wisdom goes, the upstream sensors are the critical ones.
 

Maverick6587

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If you're getting lean codes, I would search for the vacuum leak first. Easier work than just replacing 2 or all of the O2s.

Edit: I guess the lean code could be from the bad O2 sensor. I'm not sure how the pcm responds to bad O2s. It should just use the other bank for data.
 
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You'll forgive my mild protestations, but... you mentioned both the bank 1 sensors were dead...but now say that I need to track down vacuum leak(s) ?

I appreciate you trying to save me from the parts shotgun...but if the sensors are dead, they need to be replaced in any case, do they not?

Guessing (I use that word a lot in this thread!) that the vacuum leak is probably coming from the area of the intake. That's usually a good place to start.

If my buyer consummates the deal for the other truck tomorrow as scheduled, you're going to see me start acquiring parts for my planned build for this truck, which will include replacing the intake with one from a TBSS that I've been holding onto for awhile.
(IOW, I'm probably not going to spend a lot of time tracking down said vacuum leak.) :wink:
 

Maverick6587

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If your O2 sensors respond and actualy start movement when you hit the throttle, I would say you have a bad vacuum leak on bank 1.

Edit: they may not actualy be bad, it could just be the vacuum leak.
 
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Ok. Now my curiosity is aroused enough to get dressed again and check this tonight. Will report back w/ result. Maybe I'll grab a screencap w/ Torque, if there's a change.

I've seen your responses to others' issues, and they were pretty spot-on. So I know you're not blowing smoke (pun intended). Glad you decided to play in my thread... :tiphat:
 
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Well.... they *do* move on the graph, when I increase to 1500-2500 rpm.

I did take a couple of screencaps and will add them later, once I get them over to my laptop.
 

Maverick6587

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Okay, maybe good news... Start with cleaning the MAF (Probably good since it's a bank specific issue). Unplug the MAF and see if the code switches to back 2 or no change. It's still going to depend on what kind of movement happened though.

I'm not as familiar with the 5.3 and 6.0, to check for leaks, as I have the straight 6. Use propane, brake parts cleaner, or soap and water to check for the vacuum leak.

Keep us posted though and good luck.
 

Mooseman

Moderator
For bank 1 sensor 2, it's normal. It's supposed to be flat, which shows the cat is working. However, bank 2 sensor 2 looks like sensor 1, which means the cat isn't cleaning the exhaust. You could further check by using an IR temp gun on the cats. Temp after the cat should be higher than before with engine reved steady to 2000.

Your trim is whacked. It's dumping a lot of extra fuel to try to compensate for the lean condition or, as mentioned, the O2 sensor is not reporting properly. Check for vacuum leaks. After that, I'd replace at least the bank 1 sensor 1 which is flatlined. Oddly enough, it's also bank 1 sensor 2 that's flatlined but it's supposed to be.
 
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After my test last night, I ran into a YT vid from a guy detailing "top 10 issues w/ LS engines". Guess what #1 was? Intake leaks. Prime symptom? Rough idle when cold. Seems to match up pretty good with this conversation, too.

So... maybe item #1 on *my* to-do list would be to replace the manifold gasket (and keep the stock intake in place, so as not to introduce too many variables -- I can introduce the TBSS intake when I embark on the other upgrades) After that, *then* evaluate the O2 sensors again (expecting that I'll have to replace the upstream B1 sensor, but we'll see)

Before I take apart anything, I'll use the appropriate sprays in the area to see if I can detect any idle changes. But it's likely the culprit here.

Guy who owned it before me said he got lousy gas mileage; he thought it was the gearing, when I revealed to him it had a 4.10. Cie la vie... :blinkhuh: I'm guessing those 315/70/17s he had on the truck, as well as the Flowmaster, had something to do with it, too - I find myself *wanting* to step on the go pedal with it attached.

And, as I write this, I'm realizing now that even with my fairly light foot, FE is wack on this motor, compared to the other 6.0L in the stable (which is starting to worry me that it's still going to be 'in' the stable at EOD today) :sadcry:

Not that the one I'm selling is great, but at least I know it doesn't have an intake leak (thx to the mech who redid the gaskets on the upper half of the motor (the part I could have done) when I asked him to fix the leak at the pan (which is still there) But I digress.

Thanks to you two, as always.

Oh -- and just for reference, & because I promised it, here's a shot of the off-throttle on the bank 1 sensors... this was at approx 2500rpm, although 1500rpm was very similar.

87866
 
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Mooseman

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Now your B1S1 seems to be working but who knows if it's the vacuum leak that's doing that at idle. I've never seen what an O2 sensor looks like with a bad vacuum leak. That last screenshot almost proves that the cat is dead. After fixing everything else, this would be the last thing to look at.

Good catch on the intake gasket. We were in the right direction looking for a vacuum leak and that is a very common issue.
 
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Just a quick update...
Got a can of carb / TB cleaner, put a fire extinguisher on standby (since ppl recommended it), fired up the scanner, activating the bank 1 fuel trims, and started the truck.

Started spraying...and when I got the spray in the right areas, watched the short-term trim fall from a +/- '0', to somewhere around -20 (remember, the long-term is pegged at +25 right now). Stopped spraying...short-term climbed back up. Resprayed...went back down.

Suffice to say, it looks like new intake gaskets are in my future. Need to shuffle all the vehicles & put this one back in the garage. Have been limiting my use of this truck until I get this resolved, in hopes of the cat(s) not being totally toasted. Sad thing is, right now, I really don't have a lot of time to work on this truck, and won't for about 2-3 weeks. Grrr...

Thanks again to both of you for your help. And for those who are interested, South Main Auto channel on YT has a great video on this type of stuff. The example there isn't quite the same (e.g.; not a true 'manifold' leak...but he does go into his usual in-depth on the problem. Well worth watching (personally, I think he has the best mechanic-type channel on YT, especially for diagnostics. He's funny, too)
 

Maverick6587

Well-Known Member
Depending on where the leak is and if it's even reachable. You could try to put some high temp silicone on the areas where it's leaking, for a short-term "fix."
 

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