O2 sensor data with P0420, bad cats?

[B.E. Coyote]

I am getting a p0420 code and the jeep runs hot under load but cools down at idle even with the AC running. This shows all 4 sensors at about 1500 rpm. The intake of both sides of the pre-cats are hotter than the exhaust side.

Could this be causing the rise in temperature under load? (Coolant temp using the Torque app)
Since both banks are reading kind of the same could it be that maybe the pre-cats are good and the third cat is bad?
Does the hotter intake sides vs exhaust indicate a clog?

 

[B.E. Coyote]

Is it strange that both banks look similar but only getting a code for one? A leak or bad sensor would not account for the heat difference, correct?

 

[macleanflood]

Trending below .9v. Looks good to me.

What year and engine?

-Mac

 

[B.E. Coyote]

03 with an auto, 103k. I thought the down stream sensors were supposed to be flat?

 

[macleanflood]

This was my 97 with a bad downstream O2.

After I replaced it...new one was also bad...

-Mac

 

[B.E. Coyote]

But my down stream sensors more or less mirroring the upstream sensors point to bad cats, correct?

This was my 97 with a bad downstream O2.

View attachment 691739

After I replaced it...new one was also bad...

View attachment 691740

-Mac

 

[macleanflood]

I don't know enough to determine that from the ODB data.

@GoldenGorilla might know.

I'd probably test my cats with an IR heat gun or back pressure gauge.

Or pull an O2 sensor and cause an exhaust leak and see if it runs better.

-Mac

 

[B.E. Coyote]

Thanks, I did do a laser thermometer and I am seeing hotter temps on the upstream side. I already ordered a set of Wagner pre-cats and will put them on next week. This in addition to a recurring p0420, I'm pretty sure the a replacement is due.

I'm also chasing down high coolant temps and hoping that this is at least part of my problem.

 

[macleanflood]

My no formal education in auto mechanics all self taught opinion would agree with you. =)

-Mac

 

[GoldenGorilla]

But my down stream sensors more or less mirroring the upstream sensors point to bad cats, correct?

The downstream O2 aren't flat, but don't move in lockstep with upstream and usually don't peak as high. It's odd that downstream mirrored the rich peak when upstream hit .8 if the cat and O2 were given time to warm up.

It would be a bit more obvious with P0431/P0432 where it indicates a bank failed. P0420 is a system efficiency failed code.

You can use the IR temp sensor method on the upper cats if your tool goes to very high temps. Or you can use the boroscope method I mentioned in the thread titled "self-immolation" to look through the O2 bung hole and confirm without removing the precats.

Sorry it's a busy graph, but I've placed O2 sensors in their pairs here. You can see upstream and downstream are swinging opposite directions at time here in section 2 and 3 of the graphed chart v time section of VCM Scanner.

I'm not running a stock 4.0L setup right now and I live at high altitude. Larger than stock injectors, Edlebrock head with thinner head gasket for higher compression, 1.7 roller rockers, headers, 2.5" exhaust. I'm fine tuning this tune.

 

[B.E. Coyote]

The downstream O2 aren't flat, but don't move in lockstep with upstream and usually don't peak as high. It's odd that downstream mirrored the rich peak when upstream hit .8 if the cat and O2 were given time to warm up.

It would be a bit more obvious with P0431/P0432 where it indicates a bank failed. P0420 is a system efficiency failed code.

You can use the IR temp sensor method on the upper cats if your tool goes to very high temps. Or you can use the boroscope method I mentioned in the thread titled "self-immolation" to look through the O2 bung hole and confirm without removing the precats.

Sorry it's a busy graph, but I've placed O2 sensors in their pairs here. You can see upstream and downstream are swinging opposite directions at time here in section 2 and 3 of the graphed chart v time section of VCM Scanner.
View attachment 693165

I'm not running a stock 4.0L setup right now and I live at high altitude. Larger than stock injectors, Edlebrock head with thinner head gasket for higher compression, 1.7 roller rockers, headers, 2.5" exhaust. I'm fine tuning this tune.

Thank you, I checked out your immolation thread too.

If I am understanding your graph both down stream 02 sensors are pretty constant or at least seem to be independent of the upstream sensor where mine do pretty much mirror the upstreams.

My jeep is running pretty hot so I took those readings after idling for 10 minutes or so and then driving it at around 1500 rpm. When I got back I left it idling and used my HF infrared thermometer to look at the cats. The high sides were hotter than the low sides but my temps were only in the high 500s I believe. I couldn't take it on a real hard drive because I was afraid of over heating.

I do have a bore scope but it is kind of thick, I'll see if it will fit in the 02 sensor hole.

Are you thinking that my cats might be okay by my 02 graph?

 

[B.E. Coyote]

@GoldenGorilla

So what am I looking at here? Would these be causing a restriction? They don't look great to me. At this point I am hoping they are plugged, I already bought the replacement and had some hope they are part of my running hot problem.

This is the pre-cat in the rear. Cylinder 4-6 I guess

Top of the cat

Exit

 

[GoldenGorilla]

The healty precat should look like this.

Failed precats tend to do this - They crumble out of position and lodge at the exit.

If you move the camera around, do you seem more defined channels? If not, it does truly look like upstream pre-cat 2 is clogged, possibly with soot. The bigger question then is why?

Do you drive in extremely dusty conditions with an intake vacuuming up the dust as you go? (kidding)

Do you have alot of oil blow-by in the intake from the CCV? And do you use a high zinc oil like diesel engine oil?
Do you lose more than a Qt of oil between oil changes?
Do you have blow by at the rings? Compression test or better - leak down?
What do your plugs look like?

 

[GoldenGorilla]

PS, I know boroscope resolution is not amazing. The photos above were from my cell after the cats were out.

 

[B.E. Coyote]

While watching the video on the scope, I got the impression that the pic I posted was pretty typical of the condition. I will attach 3 different pics but they all kind of show that one semi open spot and the outside seems kind of closed up.

I bought the jeep late fall and have been working on it ever since. I doubt that I have 100 miles on it. The plugs were definitely worn and out of gap but not burned up or covered in oil. The previous owner had 35" tires on it with 3.73 gears, maybe the engine lugging could cause it? I now have 33's and 4.10 gears

I'm mostly chasing the fact that it runs hot. I did a chemical block test that seemed fine, I don't get any other codes than that p0420.

 

[B.E. Coyote]

Jeep only has 100k on it, if that makes a difference....

 

[GoldenGorilla]

Going back to overheating, it's expected for these to run in the 195-225F range. If you're in that range, you're not overheating. 210 - 215 are pretty normal for people. Mine has always been on the cooler end of the spectrum, though always signaled 210 in the dash.

Mine died around 80k. I'm owner 1 and have taken good care of my TJ. I don't think it matters. I thought it may have been influenced by an intake leak, but on inspection in disassembly saw no evidence of that.

Assuming based on the timestamp that the first 2 images above are from the same cat, then I would say probably not clogged. And not structurally compromised. It's just bad jpeg compression blurring the channels in the cat. Hotter just above vs below is still a bit concerning.

I'm not sure on the next step, but before tearing it down I might consider a bit more diagnostic work. Check the cold exhaust for leaks with a leaf blower up the tailpipe and soapy water at the joints. Check intake for leaks with a smoke tester, or maybe the leaf blower in the intake and soapy water? Inspect the fuel injectors. Plugs seem fine.

 

[B.E. Coyote]

I'll do some more driving. Before I changed the fan clutch it would definitely get too hot too fast. Now once I see 225 I'll put the heat on, pull over or Rev it in neutral. I don't know how hot it would actually get if I just drove. My dash gauge never really goes above the 210 marque but I'm now paranoid and looking at my torque app.

I bought a gauge today at HF to check the pressure above the pre cats. That seems like it would be pretty definitive. Ill also see if I can get some pics of the top of the other cat. Ill try video too but the other cat will be more awkward. I'll also run the output of my shop vacuum through the tail pipe to see what I can see.

I have a new set of Walker pre-cats in the garage now and a koyorad coming soon.

Leaving town tomorrow for a week. Probably good to walk away from it for a bit anyway.

I really appreciate the advice.

 

[B.E. Coyote]

So, I did the borescope back into the bank 2 cat. This time I used video instead of still pictures. It was actually good. No new pictures for it.

Bank 2 explained the p0420 code

Top

Bottom

So at least I didn't buy the new cats for nothing. The HF kit that I bought did not come with the right 18mm adapter for the pressure gauge so I could not test the back pressure.

With the hole in the bottom of the bank 1 cat also that could mean the third cat is plugged and effecting both of the others so I still want to do that pressure test but I imagine that I would also be able to see the damage to the third cat once I take it apart.

At least I finally feel like I am getting somewhere.

 

[GoldenGorilla]

Oh, that's coming apart. Bad bad bad