Should I install missing catalytic converters?

[TJMexico]

When I bought my 2006 TJ last year, I didn't realize that it was missing two of the three catalytic converters. I'm pretty sure it's the two pre-cats that are missing.

I'm running 31x10.5/15s with a 4.0l engine coupled to an automatic transmission.

My fuel consumption is decent. I don't remember what I get on the highway, but I mentioned it once here and folks were impressed. A long off-road trip that I make regularly is nearly 200km (about 120 miles) and I get home with a quarter tank left. The road is very rough and I spend most of the time in lower gears and a good part in 4wd with a whole bunch of up and down and a lot of ascent on the way out.

The engine seems to run smoothly.

Of course the check-engine light stays on. The only code it throws is P0161 (O2 Sensor Heater Circuit).

Can anybody think of any reason to replace those pre-cats? Or should I just let that sleeping dog lie?

Note that there are no legal ramifications here to not having them. If I were in the capital city, then they'd check them. Here in Sonora there is no kind of inspection and no legal requirement.

 

[Chris]

I can't think of any reason to have them.

 

[JKP]

It would be expensive to turn off the light. It will not hurt a thing running without them.

 

[Weasellee]

I removed all 3 cats and no CEL. I don’t try to explain it.

 

[macleanflood]

I'm good with the one that's on my 97. It's down near the transfer case. I used an aftermarket high flow.

-Mac

 

[Plumber1]

Does your state not require smog checks ??

 

[TJMexico]

Does your state not require smog checks ??

I live in NW Mexico. Commented in my OP that it is not legally required here, at least there are no mechanisms in place to check it.

 

[Plumber1]

I live in NW Mexico. Commented in my OP that it is not legally required here, at least there are no mechanisms in place to check it.

Sorry that's what I get for not reading your post all the way I saw your avatar and thought New Mexico not NW Mexico

 

[TJMexico]

It would be expensive to turn off the light. It will not hurt a thing running without them.

Remember back when the dash lights were accessible from underneath and you could just reach up behind the dash and pull them out to replace them?

I had a weenie riding with me once in my old GMC pickup. I had just done a brake job and there was a tiny bubble in one line, so the brake light was on. Brakes were working fine and I just had not had a chance to finish bleeding them. Weenie kept looking at that light, real nervous like. I asked if he thought we needed to fix it and he said, Yes!

I stopped the truck and made a big production of getting out, reaching up under the dash and pulling the bulb. Handed the bulb to him and said, "There, problem solved."

Weenie was not impressed.

 

[TJMexico]

Sorry that's what I get for not reading your post all the way I saw your avatar and thought New Mexico not NW Mexico

Yeah, the NW does get confused with New. No worries...

 

[TJMexico]

I removed all 3 cats and no CEL. I don’t try to explain it.

It's a miracle!!!!!

Thanks for all the feedback. I have often heard that lacking cats could cause back-pressure issues that can cause problems. But sounds like we're good - all of us.

 

[GoldenGorilla]

When I bought my 2006 TJ last year, I didn't realize that it was missing two of the three catalytic converters. I'm pretty sure it's the two pre-cats that are missing.

I'm running 31x10.5/15s with a 4.0l engine coupled to an automatic transmission.

My fuel consumption is decent. I don't remember what I get on the highway, but I mentioned it once here and folks were impressed. A long off-road trip that I make regularly is nearly 200km (about 120 miles) and I get home with a quarter tank left. The road is very rough and I spend most of the time in lower gears and a good part in 4wd with a whole bunch of up and down and a lot of ascent on the way out.

The engine seems to run smoothly.

Of course the check-engine light stays on. The only code it throws is P0161 (O2 Sensor Heater Circuit).

Can anybody think of any reason to replace those pre-cats? Or should I just let that sleeping dog lie?

Note that there are no legal ramifications here to not having them. If I were in the capital city, then they'd check them. Here in Sonora there is no kind of inspection and no legal requirement.

It might not have come with pre-cats if originally sold for the Mexican market. There are other international markets like Japan where only the main cat was installed and there were straight downpipes instead of pre-cats.

As for the O2 sensor heater code- It doesn't have anything to do with the precats or lack thereof. It's likely because a Bosch or other non-NGK/NTK unit was fitted. The Chrysler method of checking the O2 sensor heater indirectly makes these very particular about the installed sensor.

 

[TJMexico]

It might not have come with pre-cats if originally sold for the Mexican market. There are other international markets like Japan where only the main cat was installed and there were straight downpipes instead of pre-cats.

As for the O2 sensor heater code- It doesn't have anything to do with the precats or lack thereof. It's likely because a Bosch or other non-NGK/NTK unit was fitted. The Chrysler method of checking the O2 sensor heater indirectly makes these very particular about the installed sensor.

Thanks.

I was told that they were removed, but that well may be the case.

I see if changing the O2 sensor or sensors is worth the bother. As the engine is running fine, it's probalby not worth the cost and effort, though.

 

[GoldenGorilla]

I see if changing the O2 sensor or sensors is worth the bother. As the engine is running fine, it's probalby not worth the cost and effort, though.

This is generally true. The fuel calculations are made only on the signals from the upstream sensors - the ones above the pre-cat if they were in place. When a downstream sensor is out, the vehicle will pretty much ignore it. It uses those downstream sensors to ensure that the cat is functioning as expected. Mostly.

 

[Weasellee]

It's a miracle!!!!!

Thanks for all the feedback. I have often heard that lacking cats could cause back-pressure issues that can cause problems. But sounds like we're good - all of us.

I removed the last (third) one when diagnosing run issues. Turned out it was packed clogged and once removed the air flow was like adding 10 Hp

 

[GoldenGorilla]

I removed the last (third) one when diagnosing run issues. Turned out it was packed clogged and once removed the air flow was like adding 10 Hp

It's worth mentioning that removing a properly functioning cat on a modern gasoline engine has no perceptible impact on performance. Tests repeatedly show a gain is only 1-3 hp. The tailpipe emissions are just worse.

We figured out how to make them do their job without restricting flow a long time ago, but it's hard to break the easy narrative that cats killed the muscle car, which even then wasn't the whole truth.

 

[ColoJeep]

It's worth mentioning that removing a properly functioning cat on a modern gasoline engine has no perceptible impact on performance. Tests repeatedly show a gain is only 1-3 hp. The tailpipe emissions are just worse.

We figured out how to make them do their job without restricting flow a long time ago, but it's hard to break the easy narrative that cats killed the muscle car, which even then wasn't the whole truth.

Modern honeycomb cats work pretty well and have reasonable flow rates , the old 2 1/4 " single exhaust pellet bed on a 350 , not so much .

 

[mrblaine]

New Mexico not NW Mexico

Easy mistake since there really is not a lot of difference.

 

[mrblaine]

It might not have come with pre-cats if originally sold for the Mexican market. There are other international markets like Japan where only the main cat was installed and there were straight downpipes instead of pre-cats.

As for the O2 sensor heater code- It doesn't have anything to do with the precats or lack thereof. It's likely because a Bosch or other non-NGK/NTK unit was fitted. The Chrysler method of checking the O2 sensor heater indirectly makes these very particular about the installed sensor.

Or, OEM sensors and the TSB for the heater circuit rewiring hasn't been done.

 

[mrblaine]

This is generally true. The fuel calculations are made only on the signals from the upstream sensors - the ones above the pre-cat if they were in place. When a downstream sensor is out, the vehicle will pretty much ignore it. It uses those downstream sensors to ensure that the cat is functioning as expected. Mostly.

It seems to reason if his came without cats, they would only run the upstream and not both. He can check that.