Converter missing, any issues?

The 97 XJ that I bought a few weeks ago is missing the converter. The PO just welded in a straight tube. There are no check engine light issues and it runs very strong. Should I just leave it off? I would like to replace the stock muffler on it since it has a small leak and sounds like an enraged bumble bee buzzing when I accelerate!

Guess I should mention I live in Michigan and we don't have smog testing.

Also, what's a decent sounding muffler (not too loud) with good flow? Nothing too expensive. Yes, I want my cake and be able to eat it too!

Thanks!

You should put it back on. You are still violating Federal Emissions law by having it removed, plus your Jeep will likely run better with it.

I'm not an enviro-nazi, but I don't like doing anything that gives ammo to them about why four wheelers are horrible people out to destroy the environment.

Running with out the cat will not hurt the motor or polute the environment any more than any other car out on the road. I have run with no cat for 5 years now with both the factory 4.0L and also a 4.6L stroker motor AND I pass the emissions test. Anybody who says you polute more by not having the cat are full of crap. If you maintain your vehicle by keeping up to date with oil changes, run good quality gas, clean the air filter, and keep the spark plugs and wires changed as spec'd the motor will run just fine.

Its the people and motors who do no maintain them or keep them in good tune that polute.

As for a good muffler, the Dynomax super turbo is a decent muffler thats quiet and still has some growl to it. I run a Spintech muffler and its pretty wicked loud but they have some quiet models as well.

AARON

I have a 97, after some fun off road I had to drive with a cat for 3 days. milege was cut atleast in half.

the check engine light maybe disconnected, or it may not be understanding the problem yet, needless to say your 97 was designed to get a reading from a downstream O2 sensor which will tell your ECU to mix more air or fuel as required. otherwise it runs in a standard loop which drinks gas much faster than when its running properly.

get a cat, search the site for a muffler (plenty on here) and I would expect to see an increase in milege which is always good.

mine came with no cat when I bought it and had no check engine light to find they just removed the bulb from the check engine light.I want to replace the cat but havent found one yet.I have read it need to be there to run the engine at optimal performance.

otherwise it runs in a standard loop which drinks gas much faster than when its running properly.

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I recently got 21 mpg checked by gps and calculated properly with 168,000 miles on my 4.0L. I have a hard time believing I will ever get better mpg than that!!

As far as the missing bulb, the engine lights turns on when the key is in the 'acc' position and turns off at start up, so the bulb is there......

The engine runs phenominal and has tons of power with no lag or sputter whatsoever. I was mainly inquiring if there was any long term effect from not running a cat. I also beleive ever vehicle is different and behaves differently to change.

I can't speak for the '97, but on my '91, the thing is going through fuel like there is no tomorrow (with no cat).

Mine has only been without a cat for about three days, -and I have decided that one is going back on. As far as how the engine runs, -I seem to have lost that "outta the hole punch/torque" that the ol' 4.0 is famous for, but on the upper-end, she runs sweet.

It seems strange, but I seem to have lost some fuel economy. I spoke with a good friend who is an ASE mechanic that is no stranger to the 4.0, and he told me that the ever so slight amount of backpressure that the cat provides effectively "alters the valve timing" giving the 4.0 the bottom-end punch that it's so famous for. He also said that the O2 sensors are usually much happier when they're good and hot, and that removing the cat will in fact reduce the EGT in the head pipe.

My idle fuel mixture seems on the rich-side with no cat, -and the ASE guy told me that is perfectly normal (assuming the coolant temp is where it should be at 190F).

I'm picking up the new cat this afternoon and should have it installed before this weekend. I'll try to remember to report back on what happens.

I know the later model rigs have the downstream O2, -and I'm not familiar with how that setup would respond, but on my '91, it runs like an uncaged animal (despite losing some of it's low-end grunt), and it is using lots of fuel, and the exhaust at idle is a little stinky.

My .02

MrShoeBoy said:

Running with out the cat will not hurt the motor or polute the environment any more than any other car out on the road. I have run with no cat for 5 years now with both the factory 4.0L and also a 4.6L stroker motor AND I pass the emissions test. Anybody who says you polute more by not having the cat are full of crap. If you maintain your vehicle by keeping up to date with oil changes, run good quality gas, clean the air filter, and keep the spark plugs and wires changed as spec'd the motor will run just fine.

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Care to back this up with some proof?

You may have passed the test, but your exhaust stinks and you're probably still at the upper limits of what is acceptable.

backpressure that the cat provides effectively "alters the valve timing" giving the 4.0 the bottom-end punch

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Sad... how the hell did he get Certified if he talks Nonsense ! ? ! ? ! How the Hell could it change the Valve timing ? was the cat connected to the timing chain ? Lmao... Give me a break

Back Pressure Sucks, anyone that claims otherwise has no clue what they are talking about, they are confusing it with exhaust velocity and scavenging... Reset your puter after removing the cat and reap the benefits, they do NOT help performance in any way.

~Ace~~ said:

. Reset your puter after removing the cat and reap the benefits,

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What benefits? Have a dyno sheet?

Other than butt dyno, nobody has offered concrete proof of benefits.

ratman572 said:

It seems strange, but I seem to have lost some fuel economy. I spoke with a good friend who is an ASE mechanic that is no stranger to the 4.0, and he told me that the ever so slight amount of backpressure that the cat provides effectively "alters the valve timing" giving the 4.0 the bottom-end punch that it's so famous for. He also said that the O2 sensors are usually much happier when they're good and hot, and that removing the cat will in fact reduce the EGT in the head pipe.

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Not to be offensive, but your friend is an idiot. I've run without a cat four times, all four because I broke it on the trail, it clogged, i pulled it and removed the guts to get home. *MASSIVE TORQUE INCREASE*. I lose some top end economy with it, though.

And seriously? change the valve timing? If you have even a basic understanding of exhaust scavenging you'd be laughing at him.

I'm picking up the new cat this afternoon and should have it installed before this weekend. I'll try to remember to report back on what happens.

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Ratman, please do! I am very curious in a non confrontational want-the-facts way!

Seems I have sparked an age-old arguement. I had a similar expierence with removing a cat on a 1996 dodge ram with a 360. My buddy / mechanic removed the 'guts' from the cat so it was basically a hollow cavity (cut it open and removed everything then welded it up - it was clogged BAD). I don't know what he did with the computer to compensate or anything, but my gas mpg went up a couple and the power was VERY noticable (compared to when the truck was new - 15,000 miles before it clogged).

Again, I'm not claiming this happens for everyone, just my personal experience.

~Ace~~ said:

Sad... how the hell did he get Certified if he talks Nonsense ! ? ! ? ! How the Hell could it change the Valve timing ? was the cat connected to the timing chain ? Lmao... Give me a break

Back Pressure Sucks, anyone that claims otherwise has no clue what they are talking about, they are confusing it with exhaust velocity and scavenging... Reset your puter after removing the cat and reap the benefits, they do NOT help performance in any way.

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explain how to reset the computer so the light goes out will ya?

The guy merely stated that the slight backpressure HAD THE SAME EFFECT as altering the valve timing, -that isn't hard to understand, -considering all gas truck engines typically have small-ish exhaust ports (for a reason).

As far as my bottom-end torque loss goes, -it's for real guys. My butt-dyno tells me that the punch that I used to have right out of the hole is nearly gone. At around 2500 RPM though, -it's a different story. Catless, my 4.HO runs better in the midrange and on the top, -but that isn't where I operate it most of the time.

I am being totally non-confrotational about this, and merely reporting my findings. I'm an ex-hotrodder from way back, -and believe me, I was kind of disappointed what happened when the kitty got lost on this rig.

Maybe guys with different years of rigs will have different results than mine, -who knows.

I surely can't afford to keep shoving gas in this thing at the rate it's going through it, -I know that for certain.

I'll be objective, -no BS here, -I'll let you guys know what happens when I throw one back on there.

I may possibly be having other issues. I replaced the O2 sensor for good measure, -didn't seem to change anything, -the water temp is good and hot, and the IAC stepper/valve is operating just fine.

Ideas?

What benefits? Have a dyno sheet?

Other than butt dyno, nobody has offered concrete proof of benefits.

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Anyone with a Mild understanding of Volumetric effeciency would not ask such a question, Anything that restrists flow, even mildly does NOT Help a motor, now, to clarify this, the computer in said car may Want to see the effects of the cat, but it Does decrease effeciency, Period. I do not need a Dyno to tell me Basic, Obvious things.

Cats do, in some cases help reduce emissions. But quite often they are responsible for Creating more than they reduce, by making the motor run at a much lower VE level.

That said... Disprove it ! Find ANYONE with 1/2 a brain that has Added a Cat to a vehicle to Help Performance Lmao... Ever seen a race car ? Buggy ? Anything with a Cat ? NO.... and with good reason. ~Ace~

IslanderOffRoad said:

What benefits? Have a dyno sheet?

Other than butt dyno, nobody has offered concrete proof of benefits.

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exactly!!!I wish someone would do a dyno run with cat and without.....put this to bed once and for all....

~Ace~~ said:

Anyone with a Mild understanding of Volumetric effeciency would not ask such a question, Anything that restrists flow, even mildly does NOT Help a motor, now, to clarify this, the computer in said car may Want to see the effects of the cat, but it Does decrease effeciency, Period. I do not need a Dyno to tell me Basic, Obvious things.

Cats do, in some cases help reduce emissions. But quite often they are responsible for Creating more than they reduce, by making the motor run at a much lower VE level.

That said... Disprove it ! Find ANYONE with 1/2 a brain that has Added a Cat to a vehicle to Help Performance Lmao... Ever seen a race car ? Buggy ? Anything with a Cat ? NO.... and with good reason. ~Ace~

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No shit.

But this is a Jeep we're talking about.

My point is this. Are those 3 hp you're picking up by pulling your cat out really going to be something measureable, that makes a difference when you drive it?

Please explain to me how a cat makes the engine pollute more. That should be a good laugh.

Here is what the ultimate understanding of my position should be. Yanking your cat may give you 1-2hp that you'll never really feel. But it makes us all look bad, give the greenies more ammo for us being irresponsible, it is illeagal, and it can lead to more trail closures.

Is 2hp really worth having nowhere to wheel?

Camo-5 said:

The 97 XJ that I bought a few weeks ago is missing the converter. The PO just welded in a straight tube. There are no check engine light issues and it runs very strong.

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On a hilarious note, I thought up through this point in his original post, that he was talking about the TORQUE converter. :wierd:

Just from my personal experience.....

I dented the cat in my 2000 enought that it broke the matrix (or whatever you would call it) in the cat free in a bunch of pieces. It would push to the back under engine load blocking the exhaust at severely restricting power (made a nice hissing noise, too).

As a short term fix, I gutted the cat housing put it back on until I decided what to replace it with. The car ran great, no power loss, no burnt up valves, no whatever else all of the old wives tails are..... I had this same argument back then on the Colorado4x4 boards.


I did run it through Colorado emissions (they put your car on a dyno and run it up through 65-ish miles per hour) and passed with relatively low numbers (at least in the lower 1/2 of the allowable range), not the upper limits. On my 2000, there was not an o2 after the cat so the computer would never know anything different. This is the same on my 2001. I do believe there are pre-cats at the exhaust manifold however which may be the reason the numbers were low and the car passed??? The o2 sensors are after these.
We do have a visual emissions test, and the only reason I passed this is because the cat housing was there when they looked under the car.


This all being said, it is illegal to remove or sell a car without the Catalytic converter. I believe that the previous owner is responsible to pay to have the catalytic converter replaced (may vary by state).

ROKRWLR said:

Just from my personal experience.....

I dented the cat in my 2000 enought that it broke the matrix (or whatever you would call it) in the cat free in a bunch of pieces. It would push to the back under engine load blocking the exhaust at severely restricting power (made a nice hissing noise, too).

As a short term fix, I gutted the cat housing put it back on until I decided what to replace it with. The car ran great, no power loss, no burnt up valves, no whatever else all of the old wives tails are..... I had this same argument back then on the Colorado4x4 boards.


I did run it through Colorado emissions (they put your car on a dyno and run it up through 65-ish miles per hour) and passed with relatively low numbers (at least in the lower 1/2 of the allowable range), not the upper limits.

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And the argument that is being made is that you likely would have passed with even better numbers had you put a cat in and retested it.

For the poster that can't find a catalytic converter...where are you looking? Anywhere at all? NAPA has a small, high-flow cat that can be had with or without O2 sensor bung, and it's relatively cheap too. Low bucks for a Federally-required piece of equipment that will help reduce the pollutants out of the tailpipe without a noticeable performance hit? Sounds reasonable to me.

Jim www.yuccaman.com