Clogged catalytic converter — trying to track down the underlying problem

[orourkcd]

Hi folks, '05 TJ owner here, though I used to own a '97 TJ and an '01 XJ. Thank you so much for being such a good resource — I have used so many of these posts over the years to problem-solve issues that have come up.

My new (to me) '05 Sport just surpassed 150k miles. Over the course of the past two weeks, I replaced the PCV elbow valve (small oil leak), spark plugs (preventative - no issues), camshaft position and crankshaft sensors (CEL), and most recently installed a cold air intake. I did have to jerry-rig a grommet to get the 02 sensor to fit in the CAI, but it didn't look like there was an issue when looking at the voltage of the 02 sensors. It was running great until a P0421 code popped up, and I noticed a significant loss in power. Took it to a muffler shop and they confirmed that the cat is clogged and there are issues with one of the pre-cats.

Now, I want to make sure there are no underlying issues before I install the new exhaust system. Before the P0421 code, I did have one misfire code in cylinder 4 when I replaced the spark plugs, but I did not drive with the misfire. It was fixed right away. As far as the CEL light for the sensors, there is already a Crown OPDA installed, so I think it was just an issue with the aftermarket sensors.

What should I do to ensure that everything is okay before installing the new cats? What should I proactively replace at the same time?

 

[SPECWAR]

I’ll be first to say it, the CAI.

 

[astjp2]

Too lean wi cause a clogged cat, I fixed it with a broom handle and now it’s no longer a problem.

 

[orourkcd]

I’ll be first to say it, the CAI.

Would you recommend reinstalling the OEM air intake or is there any adjustment I can do?

 

[Zorba]

Would you recommend reinstalling the OEM air intake or is there any adjustment I can do?

Nobody here likes a CAI, for a variety of reasons.

 

[JKP]

The O2s are in the exh pipes. The only sensor in the intake pipe is the intake air temp.

The pre cats are known to crumble and then plug the cat on the skid. If it was ever driven with a misfire for a period of time, that will destroy the pre cat.

 

[astjp2]

I’ll be first to say it, the CAI.

How? It does nothing

 

[mjonesjr84]

How? It does nothing

The hot air being drawn in the "CAI" can cause the ECM to lean out the mixture because the air is less dense.

 

[astjp2]

The hot air being drawn in the "CAI" can cause the ECM to lean out the mixture because the air is less dense.

I don’t think it’s enough difference on a tj to clog a cat, now a bad o2 will wreck havoc on things

 

[mjonesjr84]

I don’t think it’s enough difference on a tj to clog a cat, now a bad o2 will wreck havoc on things

Over time, maybe. A bad upper O2 would compound the CAI issues.

 

[ColoJeep]

The hot air being drawn in the "CAI" can cause the ECM to lean out the mixture because the air is less dense.

The stock airbox draws under hood air just like a CAI.

 

[mjonesjr84]

The stock airbox draws under hood air just like a CAI.

It does, but not at the volume the CAI does being the CAI will draw air right off the engine.

 

[ColoJeep]

It does, but not at the volume the CAI does being the CAI will draw air right off the engine.

The " volume " is of air being used is determined by the engine displacement and r.p.m. only. Without a cowl or ( gasp ) snorkel intake , or other true outside the engine compartment intake situation. Also many CAI include a divider wall between the intake and engine. I would look elsewhere for a clogged cat answer. Thanks.

 

[MikeE024]

Unburnt fuel can cause the cat's PGMs to heat up and melt/clog the catalytic converter.

If the CAI was a problem (especially after only being installed for a short period of time), boosted folks running way more volume of hot air would have problems that we don't have.

I'd consider evaluating items such as your injectors, spark plugs, and piston rings.

Keep an eye out for misfires. Maybe do a compression test as well if you haven't done one in a long time. What do you your fuel trims look like?

 

[astjp2]

The " volume " is of air being used is determined by the engine displacement and r.p.m. only. Without a cowl or ( gasp ) snorkel intake , or other true outside the engine compartment intake situation. Also many CAI include a divider wall between the intake and engine. I would look elsewhere for a clogged cat answer. Thanks.

View attachment 641618View attachment 641619View attachment 641620

Slugs of air will be temperature dependent, but the pictures are not really cold

 

[SPECWAR]

How? It does nothing

You’re correct, it does nothing for the 4.0.

 

[mrblaine]

Nobody here likes a CAI, for a variety of reasons.

I don't know about all that. I'm a fan.

 

[mrblaine]

Zorba, you laughed at my post which points to you perhaps not believing me. How about now?

 

[ColoJeep]

Zorba, you laughed at my post which points to you perhaps not believing me. How about now?View attachment 641967View attachment 641968View attachment 641969

Nice work Blaine . Details like the rolled bump on the end is a first rate touch .

 

[BlueC]

Zorba, you laughed at my post which points to you perhaps not believing me. How about now?View attachment 641967View attachment 641968View attachment 641969

I've been trying to visualize how to pull air from that general area. I think you just showed me.