Do I have a bad catalytic converter?

K_Dom

K_Dom

Member
Joined
Aug 13, 2021
Messages
62
Location
Springtown, TX
I have a 2000 TJ 4.0 with the single cat. I had what I believed was a heat soak issue. I installed the DEI insulation kit and things seemed to be better. But here is my current issue. When my engine gets hot, I notice a rough idle and a loss of power at higher speed/higher RPMs. I also have occasional issues restarting the engine when hot. Just yesterday, I ran into the store after driving for 20 minutes. When I tried restarting the engine, it sputtered like a heat soak issue and then died. After several attempts, the engine would not start. I let it sit to cool down for about 15 minutes and then it finally fired right up. After that I once again noticed a loss of power at higher rpms and speed. I do not have any codes but the catalytic monitor will not pass. I meant to check if the cat was red this morning after driving to work but I forgot to check it. Does this sound like a bad cat?

Kevin
 
How’s your gas mileage lately? When mine went bad & plugged, I was getting 10-12 under all driving conditions and it was down on power/accelerating sluggishly. Once the bad cats were replaced, I was back up to 14-17 depending on city or highway and acceleration was back to normal.
 
joelachr said:
How’s your gas mileage lately? When mine went bad & plugged, I was getting 10-12 under all driving conditions and it was down on power/accelerating sluggishly. Once the bad cats were replaced, I was back up to 14-17 depending on city or highway and acceleration was back to normal.
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My gas mileage has dipped as well.
 
K_Dom said:
My gas mileage has dipped as well.
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Cats sound like a possibility then. I think another possibility could be bad O2 sensors. That might explain the hard starting when warm, which I don’t recall mine doing.
 
Usually when you have a clogged cat, they vehicle will fall flat on its face when trying to accelerate. It's won't want to rev and may stall.
It may also crank excessively.
You need to install an exhaust back pressure gauge in the front and rear O2 sensor ports and compare the readings.
Check with a local auto parts store that has a tool loan program.

https://www.amazon.com/dp/B0002SQWVQ/?tag=wranglerorg-20
Have you checked your fuel pressure?

What your describing doesn't sound like a cat issue to me. There are numerous things that could be causing your issue.
 
You need to look at live data. It's not true that you'll always get a code. The set criteria for catalytic efficiency is very specific. Live data from your downstream o2 sensors, viewed in closed loop will tell you what you need to know.
 
williambmac said:
Usually when you have a clogged cat, they vehicle will fall flat on its face when trying to accelerate. It's won't want to rev and may stall.
It may also crank excessively.
You need to install an exhaust back pressure gauge in the front and rear O2 sensor ports and compare the readings.
Check with a local auto parts store that has a tool loan program.

https://www.amazon.com/dp/B0002SQWVQ/?tag=wranglerorg-20
Have you checked your fuel pressure?

What your describing doesn't sound like a cat issue to me. There are numerous things that could be causing your issue.
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I have not checked fuel pressure. The majority of the time it starts right up even after sitting for days.
 
ItchyDong said:
You need to look at live data. It's not true that you'll always get a code. The set criteria for catalytic efficiency is very specific. Live data from your downstream o2 sensors, viewed in closed loop will tell you what you need to know.
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What should I look for in live data? Right now I can only see voltage on both O2 sensors and short term fuel trim for my upstream sensor.
 
K_Dom said:
What should I look for in live data? Right now I can only see voltage on both O2 sensors and short term fuel trim for my upstream sensor.
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If all you can see is upstream than your tool isn't sufficient. You'd need a tool to be able to graph the downstream o2 sensors. You can also buy or rent a back pressure gauge. You remove the upstream o2 sensor from the suspected bad bank and read the pressures at idle and with throttle snaps. No need to guess on any of this. It can all be tested and isolated.

Edit: to be clear, I'm not suggesting you have a bad cat based on your symptoms. I'm just addressing the question of whether or not your cats are bad, and giving you means and info to test them.

https://www.amazon.com/dp/B08XW1D7DC/?tag=wranglerorg-20
 
K_Dom said:
just to be clear I have a single cat system with 1 upstream and 1 downstream O2 sensor.
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you need to clarify. My 2000 had mini-cats and a rear cat.
You stated that you already replaced the upstream O2.
do you have 2 mini cats coming off the exhaust manifolds with a 3rd rear cat?
 
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