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How can I tell if my catalytic converter is bad?

matkal

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Michigan’s Thumb
I had a similar problem, my 04 6.0 R4LE(?) wouldn't go above 70mph in OD, but would go 80 in third. I exhausted ( :ROFLMAO: :ROFLMAO: ) all other possibilities then cut the pipe in front of the third, unmonitored cat. Which is why no CEL. It would easily go 80 in OD. BTW, I got $175 for my old cat.
 
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Turdworlder

Turdworlder

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Mar 2, 2020
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Kazakhstan
I had a similar problem, my 04 6.0 R4LE(?) wouldn't go above 70mph in OD, but would go 80 in third. I exhausted ( :ROFLMAO: :ROFLMAO: ) all other possibilities then cut the pipe in front of the third, unmonitored cat. Which is why no CEL. It would easily go 80 in OD. BTW, I got $175 for my old cat.

I tried to unbolt them, but even 1 meter breaker bar could not. I guess i will just cut
 

txbemis69

was last seen escaping the asylum
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east texas
have seen a stopped up cat choke a pontiac big block 400 to where it would barely run.
 

TexasTJ2004

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I thought that you can run exhaust back pressure test. Remove the O2 sensor and connect the tester to measure the back pressure levels
 
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TheBoogieman

Disturbed American
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C-Ville VA
First and most obvious symptoms of a cat going bad. It goes downhill from there. 🤫
badcat (2017_11_20 00_38_12 UTC).jpg


bad cat.jpg
 

P man

Keister Bunny
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Washougal Wa
I just went through this and the symptoms were as described by others..Zero power and any sort of incline would almost stop the jeep

I took a rubber mallet and smacked the converter and could hear crap falling and bouncing around

I may have accidentally cut an inspection hole in the converter body, removed the honeycomb that had fallen to the bottom and retested.
 

TexasTJ2004

I love my TJ
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I just went through this and the symptoms were as described by others..Zero power and any sort of incline would almost stop the jeep

I took a rubber mallet and smacked the converter and could hear crap falling and bouncing around

I may have accidentally cut an inspection hole in the converter body, removed the honeycomb that had fallen to the bottom and retested.

I liked the way how you used the word accidentally:)
 

Trevlaw

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Go to auto parts store, or exhaust shop. Buy an O2 sensor plug. Drill and tap for 1/8" NPT, install 1/8npt fitting with a hose barb. Buy an air pressure gauge, 0-30 or 60 psi works. Connect the two with some hose and clamps. Install in place of an O2 sensor, run engine, rev it and watch the gauge, but not long enough to melt your hose. Compare between upstream and downstream locations.

I've seen varying numbers on what's in spec at different rpms. Safe to say anything over 10 psi is plugged. Under 10 but more than 2 or 3 psi should probably be diagnosed further by other means. Temp gun or visual inspection.

When my third cat plugged I couldn't go over 70mph and had 30 psi of back pressure at 3k rpm
 

pagrey

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Apr 10, 2018
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The factory test is a pressure sensor inserted in one of the O2 sensor ports to read pressure like @Trevlaw suggested. There are details on how to perform the test floating around somewhere. The factory scan tool has a kit that does it, I think it's the oscilloscope pressure tester pep module or something like that. You might have better luck just shooting it with a temp gauge, a plugged cat will get pretty hot.
 

NskLJ

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Oct 19, 2021
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Long Beach
Is there any method to assure that my cat is clogged when there is no cel?

To check for a clogged cat install a vacuum gauge to the manifold and drive it. ( I would put it under the wiper ) hold steady throttle while driving or stationary. You will see the vacuum drop off if the cat is plugged. If you want to check cat efficiency check inlet and outlet temps. Outlet should be hotter than inlet.
 
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NskLJ

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That works too, I recommended the vacuum gauge as it is a much more common tool than a back pressure gauge. I forgot with Amazon inexpensive tools are at your door in a couple days.
 
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1515art

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That works too, I recommended the vacuum gauge as it is a much more common tool than a back pressure gauge. I forgot with Amazon inexpensive tools are at your door in a couple days.

It’s good to have options, he may already have a pressure gauge to use or prefer it.