Bank 1 downstream O2 sensor question

[Drewmcg]

I've got a code relating to Bank 1 too rich that keeps coming back despite multiple steps to correct.

Question: In recording by OBD data, I noticed that through 10 frames that the rear (downstream) O2 sensor on bank one stays pegged at approx. 0.9 volts (exactly in most frames, from low of 0.89 to a high of 0.92) across 10 frames, and reads "lean" in each frame. The other three O2 sensors fluctuate in both voltage and rich/lean as shown the recording playback on my Bosch OBD 1350 scan tool.

Does this indicate a bad downstream O2 sensor (original Ford, with 180k miles)? There has been no code shown re cat efficiency on bank 1.

 

[plasticseng]

The rear sensors should stay pretty steady.

If the bank 2 rear sensor is fluctuating up and down with the front one, that raises a concern about the condition of the converter on that side.

How much up and down do you see with the rear bank 2 sensor? Is it swinging as much as the front one?

 

[Drewmcg]

There are two downstream (each bank has one). Bank 1 is pretty steady (0.89v to 0.92v). This seems to be the upper limit of voltage on these things, non? The Bank 2 sensor fluctuates much more. Perhaps the cat on that bank is going bad? Both upstream sensors fluctuate rapidly.

 

[plasticseng]

Will that scanner graph the voltages?

 

[Drewmcg]

I haven't figured out the graphing function yet -() but additional research suggests that both downstream O2 sensors are behaving correctly. Evidently, a downstream O2 sensor that does not switch much suggests that the cat on that bank is O.K., where as one that switches a lot to match the upstream sensor indicates that the cat on that bank is bad.

So looks like I have a failing cat on bank 2 not a failing downstream O2 sensor on bank 1.

Does anyone have experience paying a shop to "splice in" (my phrase) a cat on one side versus replacing the entire y-pipe, with the two cats and resonator ($$$)? Looks like it would be tricky to do given the short length of exhaust between the exhaust manifold and the y-pipe bend, but Rockauto sells individual cats, so it must be doable. What's a good price for this? How have the results been? Preferred brands? Thanks!

 

[Drewmcg]

Okay I called around on a visit to Austin, TX, and found a shop (SOCO) on Congress north of hwy 290. They quoted a price of $295 to install a "generic" cat between the two O2 sensors on the drive side. I'll let y'all know how it works out.

BTW, I have access to a lower-mileage (116k miles) OEM y-pipe w/cats on an '02 Explorer, but the Chilton manual says you need to pull the transmission carrier to get it out. And the same on my XLS to get that one out, and the swapped one in. Watched some videos on this and it looks like a mess/PITA. So I hope this $300 solution does the trick.... My only concern is whether the failed cat dumped some metal in the third (between downstream O2 sensor and muffler) cat, creating backpressure. But the truck seems to accelerate well (though I have no real point of reference), so I'm gonna go for it.

 

[imp]

@Drewmcg
Still trying to resolve my own Bank 1 Position 2 code; only it relates to Heater Resistance only. Since beating on the cat "cured" it for over a thousand miles, then it came back, I expect replacing the cat will be necessary. Yes, individual cats are available, but welding them in may be another matter, if the original pipes are stainless steel, need to use MIG or TIG. imp

 

[Drewmcg]

What I learned: I got a call from the muffler shop mid-repair. As the service manager had warned, the failed cat (bank 2, front one between the two O2 sensors) had dumped a load of material out the back and into the third cat (the one after the y pipes join, before the muffler. He said that this (third) cat doesn't really do much, and gave me the option of welding a straight pipe in there to save $125, which sounded good to me. So total cast to splice in one new (generic) cat (bank 2) and the straight replacement pipe =$420. Ouch.

When I picked up the truck the service manager volunteered to show me the third, removed cat. Wow. Its opening was chock full of the lava-like material offloaded by the failed upstream bank 2 cat (which sits just a short ways in front of it). This must have happened relatively shortly before I took the truck in, b/c I don't see how I would have made a 1,500 mile trip with exhaust so blocked by the failed cat material clogging up that third cat. I actually noticed a strange new noise from left side of the truck on hard acceleration at the very end of my trip (i.e., pulling into my son's subdivision, the evening before I took the truck to shop). Pretty lucky; $420 well spent.

Truck runs beautifully (and quietly) now.

 

[Drewmcg]

Imp: My buddy and I had my XLS on a lift over a week ago to try to reduce exhaust pipe/cat noise. We ended up cold chiseling off the lower heat shield on the bank 2 cat, and it was, indeed, quieter.

What I now believe (see my preceeding post) is that this beating (plus age, plus 179k miles) "broke up" the material in the cat that does its job, eventually causing those chunks of material to be forced downstream into the third cat. Not good. Having briefly seen and touched this stuff, it reminded me of pumice.

Lesson learned: Not a good idea to beat on cats! Assuming you're not a glutton for punishment of trying to remove a probably-good y-pipe (with all 3 cats) from a junkyard and installing it on your 'sploder, to my mind (and even wallet), the better option is to call around to find a sensible, not-greedy muffler shop willing to splice in a generic cat for a few hundred dollars. Failing cats will only cause more problems down the road (and down the pipe).

I don't know if the exhaust is stainless, but I do know those y-pipes containing the cats are strong and thick and do not appear to rust through even for high-mileage, old, northern Exploders with lots of other underbody rust.

 

[imp]

Imp: My buddy and I had my XLS on a lift over a week ago to try to reduce exhaust pipe/cat noise. We ended up cold chiseling off the lower heat shield on the bank 2 cat, and it was, indeed, quieter.

What I now believe (see my preceeding post) is that this beating (plus age, plus 179k miles) "broke up" the material in the cat that does its job, eventually causing those chunks of material to be forced downstream into the third cat. Not good. Having briefly seen and touched this stuff, it reminded me of pumice.

Lesson learned: Not a good idea to beat on cats! Assuming you're not a glutton for punishment of trying to remove a probably-good y-pipe (with all 3 cats) from a junkyard and installing it on your 'sploder, to my mind (and even wallet), the better option is to call around to find a sensible, not-greedy muffler shop willing to splice in a generic cat for a few hundred dollars. Failing cats will only cause more problems down the road (and down the pipe).

I don't know if the exhaust is stainless, but I do know those y-pipes containing the cats are strong and thick and do not appear to rust through even for high-mileage, old, northern Exploders with lots of other underbody rust.

@Drewmcg
So it's like pumice! Interesting. Also interesting that I believe my third component under there, it's rearward of the transmission crossmember, is not a cat, but rather a plain old muffler. If partially clogged, I would expect loss of engine performance as well as more fuel consumption. I still get same old 18mpg, seems to have as much power as ever. Generally, a muffler has pretty much big passages, difficult to clog. I've cut open a few cats, and the passage ways through them were very fine, had to hold it up to a light very steady, and could barely see through the length of them.

I can see that removal of my wye-pipe will be a cut-away affair. None of the threaded fasteners look grabable by sockets. imp

 

[Drewmcg]

Not sure about backpressure. I drove over 1k miles last weekend with the bad cat, 70-75mph on interstates w/o noticing performance problems. Averaged 19-21 mpg (better mileage with windows closed and a/c on!). But it may be that the clogging of the third, downstream cat did not happen until the end of my trip, when I started to hear strange noises upon acceleration from my exhaust again . . . .

It probably depends on just how the broken chunks happen to load into the third cat, and what air gaps persist.

 

[satherman]

Sorry bout this,but I have ta ask,this being such an old Post,but relates ta where I'm at..
2002 4.0, exp, bank 1 cats gone..
Bank 2 cats remain..
Can a signal from downstream bank 2 o2,(after cat) be ganged up or spliced on to bank 1 o2,(after cat) using a diode or two?
It would seem to me that if the ECM interprets the signal from the post cat o2,and it doesn't affect the performance, could it be done? This vehicle had a plugged cat,bank 1,,which I dropped an cleared an reinstalled,
Engine runs Great, but cannot afford 300.00 fer 1 side(2cats)..
Are the post cat o2 sensors paired inside the ECM, or separate? Signal bank 2 steady,not finding explanation ,
Would appreciate the help..
Many thanx

 

[Drewmcg]

(i) I don't know the answer to your rather technical question;
(ii) are you having a performance issue, or are you trying to pass a state certification requirement (get around one, that is) with no performance issue. Not judging; just asking;
(iii) there are generic aftermarket universal cats that are way less expensive than OEM or even aftermarket ones designed for this truck. Any exhaust shop that does a lot of catalytic converter work have them either in stock or nearby. I think I paid $75 each (not counting labor, which was a lot more) for the two that have been in my '02 now for a couple of years w/o issue;
(iv) I could be wrong about this, but I don't think the downstream O2 sensors do anything for engine management (just the upstream ones, which are crucial for fuel management). The downstream ones are there to check the efficiency of the cat on each side. If it falls below a certain threshold, it throws a CEL code. In Michigan, for example, there is no annual certification, so that code (other than being annoying) doesn't really matter (unless you are environmentally conscious). What DOES matter -- for performance -- is if a cat disintegrates enough internally to block air flow (what happened to me, see above). This is usually a result of other serious engine problems that cause raw fuel to be dumped into the exhaust where it ignites and overheats the cat.

Good luck.

 

[imp]

@satherman "Can a signal from downstream bank 2 o2,(after cat) be ganged up or spliced on to bank 1 o2,(after cat) using a diode or two?"

I believe the PCM operates by continuously scanning it's program, thus "looking at" each O2 output individually, but very quickly. If nothing is found amiss, it just keeps scanning. Otherwise, a code is thrown based on what it "sees".

I don't see how the car can pass a test inspection; soon as the guy "mirrors"
under the car, sees cat missing, failed. imp

 

[satherman]

(i) I don't know the answer to your rather technical question;
(ii) are you having a performance issue, or are you trying to pass a state certification requirement (get around one, that is) with no performance issue. Not judging; just asking;
(iii) there are generic aftermarket universal cats that are way less expensive than OEM or even aftermarket ones designed for this truck. Any exhaust shop that does a lot of catalytic converter work have them either in stock or nearby. I think I paid $75 each (not counting labor, which was a lot more) for the two that have been in my '02 now for a couple of years w/o issue;
(iv) I could be wrong about this, but I don't think the downstream O2 sensors do anything for engine management (just the upstream ones, which are crucial for fuel management). The downstream ones are there to check the efficiency of the cat on each side. If it falls below a certain threshold, it throws a CEL code. In Michigan, for example, there is no annual certification, so that code (other than being annoying) doesn't really matter (unless you are environmentally conscious). What DOES matter -- for performance -- is if a cat disintegrates enough internally to block air flow (what happened to me, see above). This is usually a result of other serious engine problems that cause raw fuel to be dumped into the exhaust where it ignites and overheats the cat.

Good luck.

 

[satherman]

Thank you for your reply,
Yep,I'm in California,where smog laws apply..
However,on a 2002,there is no "probe" ,only computer interface.. OBD2..yes,there is a visual, but the cat has been gutted ( replaced hollowed out) for engine diagnosis,ta see if performed, and it does..it lacked power when I first got it,plugged cats an all.initial assessment an a brief history of the vehicle was engine went sour, they replaced the engine and trans,but not the cats..why and how this happened I'll never know, but am limited in resources to repair to calif specs..
Again,it will pass a visual,but not the downstream o2 bank 1,on a "computer only"
Smog check..
2003 and up have a countermeasure for sensors, individually tuned,from what I'm to understand..I could and have been wrong before,please feel free ta let me know..
Can a signal,from good bank 2 downstream o2, , be electricaly (wired) to bad downstream bank 1?(mirrored,so to say,in the ECM)
Kinda like an amputee with feeling of a missing limb..the ECM is looking for certain parameters,and upon finding it,cancel cel?
I'm sorry so long winded an ignorant of these things,but it would seem to me that if it did not affect a/f mixtures, the sensors would not actually contribute to it..lites come on when either door is opened,for example..
Perhaps someone out there can explain to me so I can understand, other than I'm a cheap old guy willing ta burn the planet..
Not a plug in chip,not burning programs into the ecm(flashing) but I'm not oppossed to modding the ECM(pathways,diodes,resistors) but didn't want ta go that far..I just can't afford 300 an labor,registration fees 140,then a smog check another 65,just ta have him plug 'n play the day away..the motor an trans look brand new!! 30 k, at the most..go figure..
Look ma,anudder old guy talking to himself..
Many Thanx for your time..
I hope I didn't annoy anyone..
Trust your government..
I can open any can with my p38...
And remember..
In 50 years this won't even matter..

 

[satherman]

Oh yeah,4 cats total..