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O2 sensors and catalytic converter issues?

Tiny
TOTALMC
  • MEMBER
  • 2012 CHRYSLER 300M
  • 6.2L
  • V8
  • 2WD
  • AUTOMATIC
  • 125,000 MILES
Customer replaced O2 sensors and cat on Bank One.

Still has a p0133 and a p0420 coming up.

At idle STFT's look good.
At 2500RPM, both numbers jump up into the mid 20's.

LTFT both Banks around 11.

Bank 2 O2 sensors numbers look good.

B1S1 O2 very slow to respond.

B1S2 starts at a steady.8, but then drops to.0135.

I'm stumped at what would cause a good reading 1 minute and not the next.

The dealer said he should replace the bank 2 cat, because it cannot match the flow of the newly installed cat on Bank 1. I can't see how replacing the cat on Bank 2 would have anything to do with codes and issues with bank 1.

As much input as I can get would be greatly appreciated.

Thanks in advance.
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Wednesday, February 22nd, 2023 AT 1:14 PM

10 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
Hi,

I agree. If the converter is working, the car doesn't care if it is a new one. LOL If you are holding it steady at 2,500, it shouldn't be that high.

Have you checked for any vacuum leaks or exhaust leaks pre-cat? Also, the slow to respond sensor should be replaced without question. It should respond right away. There could be a wiring issue, but also an exhaust leak can cause this to happen.

Let me know.

Joe
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Wednesday, February 22nd, 2023 AT 8:53 PM
Tiny
TOTALMC
  • MEMBER
  • 106 POSTS
I did a visual inspection for vacuum leaks; my smoke machine is basically worthless so that was as far as I could go.

Are the plastic intake manifolds prone to leaking on the hemi?

As for an exhaust leak, I tried to check, but just by ear. Any suggestions on a better method?

Thanks again.
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Wednesday, February 22nd, 2023 AT 10:02 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
Hi,

As far as the exhaust leak is concerned, it could simply sound like ticking. Also, when you check for vacuum leaks, try using carb cleaner to see if the RPMs change at any point.

As far as the intake, anything that's plastic is more susceptible to head damage.

Let me know.

Joe
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Thursday, February 23rd, 2023 AT 6:48 PM
Tiny
TOTALMC
  • MEMBER
  • 106 POSTS
Found a small exhaust leak due to a bad weld, that's taken care of.

New OEM O2 sensors on Bank 1.

Muffler shop installed downstream O2 sensor in the middle of the cat, so thinking that could have something to do with the bad readings, had it moved to the pipe after the cat.

B1S2 still slowly moving between.0135 -.880.

Still having p0133 slow response, p0420, and now a p2096. And this is the side with the new cat.

STFT's are okay at idle, both Banks still jump as high as 30+ at 2500 RPMs.

Cannot find a vacuum leak, but will search again tomorrow.

I may be able to take pictures of the graphs on my scanner's live data and post those - if that would help.

I kind of smell coolant under the hood, but no visible leaks. Smells fine at the exhaust tips, but there is some condensation, could a leaking head gasket cause any of these issues?

Also, maybe a faulty MAP sensor.
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Friday, February 24th, 2023 AT 5:24 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
Hi,

The condensation, to a degree, is normal in the exhaust. As far as the slow response, it could be a connector issue or a wiring issue.

Do me a favor. Take a look at the diagnostics that I attached below and let me know if you are comfortable performing them. Some have already been completed.

Let me know.

Joe

See pics below.
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Friday, February 24th, 2023 AT 9:18 PM
Tiny
TOTALMC
  • MEMBER
  • 106 POSTS
Okay, thanks.

I think I can perform most of that, except for the exhaust leak test. I'm a mobile tech, and I am limited in specialty equipment.
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Friday, February 24th, 2023 AT 9:55 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
Hi,

Sounds good. If you have a chance, let me know what you find.

Take care,

joe
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Friday, February 24th, 2023 AT 10:02 PM
Tiny
TOTALMC
  • MEMBER
  • 106 POSTS
Thanks Joe, will do.
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Friday, February 24th, 2023 AT 10:08 PM
Tiny
TOTALMC
  • MEMBER
  • 106 POSTS
So, it turns out the muffler shop that originally replaced the cat swapped the leads on the O2 sensors, so the upstream sensor was in the downstream position

After putting them back in order, O2 sensor voltage readings starting to look more normal, no more slow response or out of whack numbers

STFT's still get a little high at 2,500 RPMs, they get up into the teens, but they were moving into the 30's.

Fixed a small vacuum leak I found in whatever the finger thickness pipe that runs along the top of the manifold is, but I thought a vacuum leak supposed to go away as you increase RPMs, so I'm not sure if the high fuel trim numbers are something else or not.

After a drive cycle the vehicle was able to pass smog, so that's the main concern.
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Monday, February 27th, 2023 AT 1:26 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,747 POSTS
Hi,

Wow, that will certainly do it. I'm glad you got it taken care of and passed smog. Thanks for the update.

Take care and feel free to return anytime in the future.

Joe
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Monday, February 27th, 2023 AT 6:02 PM

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