I have an 06 Wrangler and got P0421 and P0431 codes, so seems like the pre-cats are done again. The first time I replaced them at 110k miles with the Walker cats until they broke at the welds at 150k, so only got 40k out of those. Replaced them with the Magnaflow pre cats, thinking they would last longer (and they did, no cracking) and now I've got the codes again at 197k miles. That's less than 50k. Luckily I'm under warranty. Is this typical? Or bad luck? I also was having an intermittent misfire at idle for a while so I'm sure that doesn't help.
Do these Jeeps go through pre-cats quickly?
- Thread starter adventureboss
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Sending raw fuel into a cat will definitely ruin it faster
KennethS
TJ Expert
Absolutely. One of my vehicles had an ignition module fail at 60 MPH - then engine stalled almost immediately, and the catalyst in pre-cat was all melted from just that brief over-rich condition.
I've never had one go bad.
p.s. Now, mine will probably fail soon.
p.s. Now, mine will probably fail soon.
Hasselblad
TJ Enthusiast
I just officially joined the failed cat club. After replacing the bank 2 sensors, I ended up with a P0421 code. The shop confirmed the cat is bad.
At least they're going to swap on the new trackbar while under there.
Aside from the codes it hasn't been running horrible, but then again I had just recently did the 5.13 gear upgrade and if it coincided with the bad cat it may have been underpowered, so maybe I can expect a lot more power once this is fixed?
At least they're going to swap on the new trackbar while under there.
Aside from the codes it hasn't been running horrible, but then again I had just recently did the 5.13 gear upgrade and if it coincided with the bad cat it may have been underpowered, so maybe I can expect a lot more power once this is fixed?
Only when the engine is dumping excess fuel into them. 290K on mine.
As others have already stated, Check your fuel management system for running rich.
A maxed out +LTFT will load the catalytic converter with fuel, reducing it’s ability to function, causing a Po42o because the downstream sensor will read a constant rich condition.
A maxed-out LTFT will cause the downstream O2 sensor to read a constant lean condition, and the lack of fuel can prevent the catalytic converter from reaching full operating temperature.
Understanding and interpreting fuel trim data can help diagnose engine issues, improve performance, and maintain regulatory compliance. Regular monitoring and maintenance of fuel trim values, along with a thorough understanding of their implications, can lead to a smoother-running, more efficient vehicle.
Long-term and short-term fuel trim effect on catalytic converter operation
Both a high and low LTFT can cause a P0420 or P0430.A maxed out +LTFT will load the catalytic converter with fuel, reducing it’s ability to function, causing a Po42o because the downstream sensor will read a constant rich condition.
A maxed-out LTFT will cause the downstream O2 sensor to read a constant lean condition, and the lack of fuel can prevent the catalytic converter from reaching full operating temperature.
Understanding and interpreting fuel trim data can help diagnose engine issues, improve performance, and maintain regulatory compliance. Regular monitoring and maintenance of fuel trim values, along with a thorough understanding of their implications, can lead to a smoother-running, more efficient vehicle.
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And likewise the very close position of the upstream o2 sensors to the leak-prone ball and cup joint will cause the upstream to see "lean" when it isn't and add excess fuel.
The cat will then get a bunch of fuel and O2.
The cat will then get a bunch of fuel and O2.
I have two TJ's. The near stock 04 TJ needed the cats replaced at around 70K miles when it was throwing codes and went into limp mode.
My 06 LJ needed cats about a month ago at 98K miles. It was getting a P0431 code.
My 06 LJ needed cats about a month ago at 98K miles. It was getting a P0431 code.
A repeated misfire is a death sentence to a catalytic converter.
Under normal, closed loop operation, the ECM constantly adjusts to make sure that nearly 100% of the oxygen is consumed each time the engine fires, but without using any extra fuel than necessary (most of the time).
Occasionally the engine will run rich for certain reasons (warm-up period, power enrichment, etc.) but this doesn't really harm the catalytic converter, just briefly increases carbon monoxide emissions. The reason this doesn't harm the catalytic converter is because there isn't much oxygen.
Likewise, running lean generally does not cause a long-term issue (just some short-term NOx emissions) because there isn't any excess fuel to burn, even if there is excess oxygen. Hence why Deceleration Fuel Cut-Off (DFCO) doesn't burn up your cats.
Meanwhile, a misfire sends both unburnt fuel AND excess oxygen to the catalytic converter simultaneously. At low power, this generally just heats up the catalytic converter to a much higher temperature than it should be, which shortens its life. At higher power, the catalytic converter heats up past the ignition point of fuel in air and causes the fuel-air mixture to detonate upstream and inside the catalytic converter.
Tha detonation plus the fact the substrate is already at an excessively high temperature (higher temperature weakens the materials temporarily) causes the catalyst substrate to fracture and spall and eventually either clog the cat or self-gut.
Under normal, closed loop operation, the ECM constantly adjusts to make sure that nearly 100% of the oxygen is consumed each time the engine fires, but without using any extra fuel than necessary (most of the time).
Occasionally the engine will run rich for certain reasons (warm-up period, power enrichment, etc.) but this doesn't really harm the catalytic converter, just briefly increases carbon monoxide emissions. The reason this doesn't harm the catalytic converter is because there isn't much oxygen.
Likewise, running lean generally does not cause a long-term issue (just some short-term NOx emissions) because there isn't any excess fuel to burn, even if there is excess oxygen. Hence why Deceleration Fuel Cut-Off (DFCO) doesn't burn up your cats.
Meanwhile, a misfire sends both unburnt fuel AND excess oxygen to the catalytic converter simultaneously. At low power, this generally just heats up the catalytic converter to a much higher temperature than it should be, which shortens its life. At higher power, the catalytic converter heats up past the ignition point of fuel in air and causes the fuel-air mixture to detonate upstream and inside the catalytic converter.
Tha detonation plus the fact the substrate is already at an excessively high temperature (higher temperature weakens the materials temporarily) causes the catalyst substrate to fracture and spall and eventually either clog the cat or self-gut.
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