HO Catalytic Converter End of Life?

[kryptronic]

I've got a 91 HO 4WD MJ with the 4.0L and an AX-15.  The truck has 231K miles on it.  I've owned it for a little over a year, and every time I've ever started it, it starts making some pretty bad noises here and there for a bit.  I think it's the catalytic converter being clogged up, but am not totally sure, as I've never had that issue.

 

Basically when I start the truck, and for about 15-20 minutes, until the truck is sufficiently warmed up (and in my mind the exhaust is at temp), the truck makes an intermittent noise that sounds like it's coming from the catalytic converter area.  This happens when parked, as well as in motion.  The noise could be coming from the transmission or engine's bottom end, I can't track it, even with an automotive stethoscope.  The noise comes and goes and the best way to explain it is it sounds like a shudder running through the whole system with some clanking and other commotion.

 

Banging on the catalytic converter seems to effect the noise somewhat when it's happening.  After a while it just goes away and the MJ will run/idle happily for hours.  It looks to be the stock cat.  So what are your thoughts?  Would a clogged cat cause excessive noise?  Would the sound dissipate as things got hot?  Thanks.

[HOrnbrod]

My original cat with the original engine was clogged, causing poor performance and overheating especially when climbing hills. After looking at everything else trying to cure this, I brought it to a friend's muffler shop in town and we sawed off the tailpipe. There was a thick black gooey mess clogging honeycomb passageways when we looked inside the cat. There was no excess noise in my case. We junked it and replaced it with an "Alabama cat" as shown below, and all was well afterwards. The cause? No idea. It wasn't using any oil, and it remains a mystery.

[kryptronic]

3 minutes ago, HOrnbrod said:

There was no excess noise in my case.

I'm getting noise but not noticing any power issues.  

[HOrnbrod]

2 minutes ago, kryptronic said:

I'm getting noise but not noticing any power issues.  

 

Understand. I'd still take a peek inside.

[johnj92131]

I remember failing my smog test 8 years (?) ago and having to replace the convertor.  Once that was done I passed smog.  Don't recall any noise, but I am half deaf.  But at 200K miles, your cat likely needs to be replaced.

 

Suggest you pick up a cheap stethoscope to try localize the noise.

Spoiler

 

 

[kryptronic]

I've got a new one here for my YJ build that I can reappropiate.  Might do it today and see what's what.

[kryptronic]

I removed the catalytic converter from the MJ.  It's internals are toast.  Looked good from the outside, but inside all the elements were cracked, apparently in many pieces inside, and it was belching dust and pieces upon removal.  Shaking it just a bit after removal reproduced what I was hearing.  I ran the MJ without it in the exhaust, just dumping right behind the downpipe, and the noise was gone.  So I'm fairly sure this was the culprit, a catalytic converter with destroyed internals.

 

So I'm going to replace it, but have run into a bit of an issue.  The stock cat has a square flange on the input side that isn't on the new cat I have.  The new cat I have, that I was going to use for my YJ, but maybe could use here, is a standard Magnaflow 91005, with a standard 2.25" input/output, without a flange.  So I'm going to have to research that and figure out if I need to get a different/new cat specifically with an XJ/MJ input flange, or if I have to use a cat like I have here, and need to cut the flange off the old cat and weld it or clamp it to the new one.  Any input would be great there.

 

Also, there is excessive play in the bushing through which the exhaust mount passes (the other half of the square flange on the downpipe, part of the transmission mount).  I think that at times the downpipe could contact the transmission crossmember with the amount of slop there.  Does anybody have a part name or number for that bushing, or a new set for the transmission mount?  91 HO AX-15 transmission mount and exhaust mount bushings, I suppose.  Again, any pointers are appreciated.

[Minuit]

3 hours ago, kryptronic said:

I removed the catalytic converter from the MJ.  It's internals are toast.  Looked good from the outside, but inside all the elements were cracked, apparently in many pieces inside, and it was belching dust and pieces upon removal.  Shaking it just a bit after removal reproduced what I was hearing.  I ran the MJ without it in the exhaust, just dumping right behind the downpipe, and the noise was gone.  So I'm fairly sure this was the culprit, a catalytic converter with destroyed internals.

 

So I'm going to replace it, but have run into a bit of an issue.  The stock cat has a square flange on the input side that isn't on the new cat I have.  The new cat I have, that I was going to use for my YJ, but maybe could use here, is a standard Magnaflow 91005, with a standard 2.25" input/output, without a flange.  So I'm going to have to research that and figure out if I need to get a different/new cat specifically with an XJ/MJ input flange, or if I have to use a cat like I have here, and need to cut the flange off the old cat and weld it or clamp it to the new one.  Any input would be great there.

 

Also, there is excessive play in the bushing through which the exhaust mount passes (the other half of the square flange on the downpipe, part of the transmission mount).  I think that at times the downpipe could contact the transmission crossmember with the amount of slop there.  Does anybody have a part name or number for that bushing, or a new set for the transmission mount?  91 HO AX-15 transmission mount and exhaust mount bushings, I suppose.  Again, any pointers are appreciated.

 

The stock replacement cats I'm seeing for a '91 MJ with 4.0L show a square flange on one end and no flange on the other.

[HOrnbrod]

I'd weld (or get it welded) the flange from the old cat to the new.

 

Are you referring to the insulator rubber, like below? If so, the p/n is 53000101 and there are plenty on Ebay.

 

[kryptronic]

47 minutes ago, HOrnbrod said:

Are you referring to the insulator rubber, like below? If so, the p/n is 53000101 and there are plenty on Ebay

 

That's exactly what I need. Thank you.  Do you have the number handy for the rubber isolator for the AX-15 trans mount too?  Might as well do both while I'm there.

 

I just ordered a Magnaflow 23229 which has the flange on it.  My research shows you either need a direct fit unit like what I ordered, or you need to extract and weld on the flange to a universal cat like the 91005.  It looks like Jeep dropped the flange line-wide for the 1993 model year.

[HOrnbrod]

25 minutes ago, kryptronic said:

That's exactly what I need. Thank you.  Do you have the number handy for the rubber isolator for the AX-15 trans mount too?  Might as well do both while I'm there.

 

The cushion for the AX-15 is the same as for the AW4, p/n 52002334.

[Eagle]

If the cat you took off is original, it has a 2-1/2" input, not 2-1/4". The factory system runs a 2-1/2" catalytic converter, and the pipe necks down to 2-1/4" between the converter and the muffler. That will make it difficult to weld the flange from your old cat onto the new one.

 

Every replacement cat I've installed came from Summit Racing and came with the proper square flange as an integral part of the converter.

[Eagle]

44 minutes ago, kryptronic said:

 

 It looks like Jeep dropped the flange line-wide for the 1993 model year.

 

I own two 2000 XJs, one early (built in October 1999), the other late (built April or May of 2000). The early one has the flange, the late one does not.

[kryptronic]

23 minutes ago, HOrnbrod said:

The cushion for the AX-15 is the same as for the AW4, p/n 52002334

 

Thank you, sir.

 

9 minutes ago, Eagle said:

If the cat you took off is original, it has a 2-1/2" input, not 2-1/4". The factory system runs a 2-1/2" catalytic converter, and the pipe necks down to 2-1/4" between the converter and the muffler. That will make it difficult to weld the flange from your old cat onto the new one.

 

I was looking at that and thinking I would have had to use an adapter pipe between the flange and the cat.  I just ordered a new one with the flange on it to save the headache.  

 

I've had several 1995 YJs and a 2000 XJ all without the flange.  First time I've come across it.  It looked to me like the part numbers with the flange only ran through 1992 for all compatible Jeep models, so I assumed Jeep made the change then.

[HOrnbrod]

3 minutes ago, kryptronic said:

Thank you, sir.

 

Please don't call me sir. I was enlisted.  

[kryptronic]

2 minutes ago, HOrnbrod said:

 

Please don't call me sir. I was enlisted.  

 

I almost wrote that you are a gentleman and a scholar instead.  But got lazy.  I appreciate the part numbers.

 

There's a bunch of conflicting info on the web as to what works and what doesn't, so you posting the right numbers here is great.  I picked up the part number for my SWB emergency brake cable in another thread and it was dead on.  Sometimes I don't even know the proper name for what I'm looking at.

[Eagle]

Don't forget the gasket for that flange. I always use new, stainless steel bolts. Doesn't seem to help much, they still get pretty well trashed within a couple or three New England winters, but it lets me feel like I'm at least trying. IIRC, the two that go through the bracket need to be 1-1/2" long and the other two can be 1-1/4". (Unless it's 2" and 1-1/2")

[Eagle]

I'll have to try to remember to look under the two 2000 XJs. After looking at the 2000 XJ parts manual, the change I was thinking I remembered may have been a change to a flange on the inlet end of the muffler, instead of a traditional male/female pipe mating.

[Jeep Driver]

You can make your own flange and weld whatever you want in it's place........any Cat for that matter. 

 

[Dzimm]

When the cat failed in my 98 xj a few years ago, I was having clanking sounds simlar to what you are describing.  Eventually I started to lose the ability to accelerate.  I finally cut it open to find the honeycomb had broken up into a ball and was clogging the output. 

 

I bought one of the cheap universal eBay cats just large enough to slide over the existing exhaust pipe and used exhaust clamps to clamp it together.  Still not having any issues with it and invested a total of about $75 into it. 

[kryptronic]

I got excited when I heard a delivery arrived via UPS today.  It should have been a Magnaflow 23229 catalytic converter.  Received a Flowmaster muffler.  What the hell, Amazon?  Still waiting on the trans cushion and downpipe isolator so not a big deal.  But still.

[kryptronic]

I just wanted to thank everybody for your insights on this one.  I replaced the catalytic converter (Magnaflo w 23229) over the weekend, along with the transmission mount (Mopar 52002334) and exhaust insulator (Crown 53000101).  As noted the catalytic converter's internals were destroyed.  Likely cause was a worn transmission mount allowing the downpipe to contact and vibrate against the transmission crossmember.  Noises reported were likely a combination of the guts of the catalytic converter rumbling around in addition to the downpipe rattling against the transmission crossmember.  More pics and specifics in my build thread, but here's a pic installed.  Thanks again.