Clogged catalytic converter — trying to track down the underlying problem

[mrblaine]

Nice work Blaine .

For the record, I've done several like that. None of them have melted cats. You can take that a few ways. We aren't introducing "slugs" of cold air, or we aren't getting any cooler air into the intake. Or, cooler air isn't responsible for melted cats.

 

[JKP]

Nice. The YJ actually has something similar from the factory, but unfortunately it's too low, behind the turn signal just above the bumper.

 

[AOSJ]

Do you burn any measurable amount of oil? Or if the cat is original, it could just be time for a new one? My 2010 Ranger never had any problems but at 180k the cat just all broke apart inside and clogged it and CEL showed P0420. A friend with the Coyote motor in a 2012 F150 burned oil a while and eventually needed to replace the cat. Motor still burns oil but he's just gonna have to replace it every so often because he doesn't want it loud.

 

[Zorba]

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

Ah, so I see. You dun it rite! Niiiiiice!

 

[jeepguy03]

The pre-cats are known to break apart like mentioned above. I started receiving cat efficiency codes on my 2000 XJ 4.0L with 140-150k miles that didn't burn any oil or have any other issues.

 

[Claybirdd]

My cats completely shit the bed all at once at 105k. I just took a 2 foot long 1.5" drill and cut the center of the matrix out. Runs better than when I bought it but the check engine light now stays on and it's a little louder.

 

[astjp2]

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

That’s how my 84 Cj was piped, from behind the headlight, I still have the plastic adapter. Have you observed measured temperature differences?

 

[Link]

Take a look at your plugs. Anything from off while to light tan is good. Black or black and oily is bad. If good, replace the cats and go on with life.

 

[astjp2]

Cold air from Cj

 

[ItchyDong]

The cold air intake has taken a beating. I’ve seen O2’s and using oil mentioned. But coolant is also a sneaky way of killing a cat.

Things to make sure.

1.) LT/ST Fuel trims are not higher or lower than a combined 10/-10 via live data. (This will either condemn or validate your intake as a cause.)
2.) Be sure your upstream O2 sensors have a healthy voltage swing from lean to rich (carbon and oxygen are the 2 things that keep a cat alive which is why the PCM varies pulse width from rich to lean in a balanced manner.)
3.) Run a coolant pressure check at the radiator to be sure you aren’t losing coolant in the cylinder. If there’s a pressure drop with no visible leaks, removing spark plugs and a bore scope in the cylinder will reveal it.
4.) Monitor oil consumption. Just like coolant, burning oil will kill a cat.

Another sneaky one is fuel additives. But it takes someone religiously adding them to a tank over a long period of time.

 

[GoldenGorilla]

Link and ItchyDong gave good advice.

The CAI is unlikely to be the culprit here. The sensor you installed in your CAI is an intake air temp (IAT) sensor. The PCM uses it plus the manifold absolute pressure (MAP) sensor to calculate the air density. It isn't going to be tricked into running lean (which can be an issue with MAF sensors), though I think the sensor in the intake manifold after the throttle body like the 04 and earlier is a little more accurate for the way these reverse flow engines like to heat the intake air at low speeds/loads.

As mentioned elsewhere, the precats do have a tendency to disintegrate themselves with time without a cause and it's quite possible it is just that. Many people replace them and have no further issues.

However bad O2 sensors, especially the 2 above the precats, a small vacuum leak at a cracked fuel injector O-ring, a small exhaust leak at the precat/manifold junction could result in the fuel trims being off, but not enough to throw codes.

You can monitor these in an app like Torque with a bluetooth ODBII scan tool. Or you can fully log them on a drive with more sophisticated tools like VCM Editor from HPTuners or a number of shop scan tools.

These vehicles are picky about their 4x O2 sensors and only like the NTK (NGK) ones specified for their designated position. You can find that part list easy enough. If you have any Bosch or other sensors in there, I'd go back to the NTK ones.

 

[NskLJ]

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 @mrblaine! Is that a windstar filter box?

 

[mrblaine]

Nice work @mrblaine! Is that a windstar filter box?

F-150 of sorts.

 

[Moglocker]

For the record, I've done several like that. None of them have melted cats. You can take that a few ways. We aren't introducing "slugs" of cold air, or we aren't getting any cooler air into the intake. Or, cooler air isn't responsible for melted cats.

Are these gonna be on your site?,does it get air above the headlight?having trouble visualizing from the pic.

 

[astjp2]

Are these gonna be on your site?,does it get air above the headlight?having trouble visualizing from the pic.

Yes the air comes from behind the headlight. That is how they did it on the last years of the CJ with the BBD carb. Pull the cold air. To pass emissions on the YJ and TJ, they used under hood air because it was consistently a smaller range of temperature.

 

[srimes]

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

Gotta appreciate a good peckerhead.

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

Yes, that's what is SUPPOSED to happen in order to maintain the correct fuel/air ratio. "CAI" kits can reduce power by sucking hot air instead of cold, but that by itself doesn't throw off the mixture.

 

[mrblaine]

Have you observed measured temperature differences?

Nope, I don't give a shit. I know I'm not pulling underhood air and that was my singular goal since the stock air box was not going to work.

 

[mrblaine]

Are these gonna be on your site?

Each of them I've done takes about a grand in time and materials.

,does it get air above the headlight?having trouble visualizing from the pic.

You don't recognize the headlight opening when there isn't a headlight bucket in it?

 

[Moglocker]

Each of them I've done takes about a grand in time and materials.

You don't recognize the headlight opening when there isn't a headlight bucket in it?

Each of them I've done takes about a grand in time and materials.

You don't recognize the headlight opening when there isn't a headlight bucket in it?

Yes I do,when the headlight and trim is in it seems like not a lot of opening for the air?that’s what I meant about hard to visualize.

 

[mrblaine]

Yes I do,when the headlight and trim is in it seems like not a lot of opening for the air?that’s what I meant about hard to visualize.

The radiator has plastic air dams that go straight in from the radiator side. Above and below them are large openings that allow grill slat air to get in and around the headlight bucket.