Super hot exhaust

[rips millar]

hey all, i'm sure this issue has been exhausted(see what I did there) but I am a noobie to xj's and a lot of answers to hot exhaust I see are that there is an obstruction in the cat. My muffler guy says that is not the case, that a blockage would not make the pipe heat up to the point of melting carpet(yes). He says look to the engine, so now I am wondering what the most likely cause is.....
vacuum leak? havent' seen any yet
no check engine light has come on...
o2 sensor? wouldn't a light come on? intermittent?
injectors?
any feedback will be appreciated.....
I began by thinking I just needed some more heat shielding down there but I did a bunch of that and it just slows the process down, the problem is the extreme heat inside the pipe not lack of shielding.......thanks

[4.3LXJ]

Exhaust can run hot. Mine does and I made a heat shield for it. But to answer your question, a lean air/fuel mixture can make it run hot as well as very advanced timing. The O2 sensor can cause a lean condition without generating a code. They only will when the heater in them fails. If it has been a long time since it was replaced, and that is the case for most, then you would probably want to change it out and start with a clean slate so to speak before going on and eliminate that possibility.

[rips millar]

ok, dumb question then, isn't there more than one? pre and post? not sure but thanks for the help, that will be an inexpensive place to start...

[4.3LXJ]

Yes, there are two. The upstream sensor is the most critical. The downstream one only measures the effectiveness of the cat. Yes, kind of expensive. But if it is worn out, replacing it pays for itself in fuel savings

[rips millar]

I also must tell you that I have aftermarket intake and a bored(?) stock throttle body which will both bring more air into the motor and there is no mechanism for the fuel system to accommodate that more air...but still, I think the exhaust is way too hot....

[Mudderoy]

Do you have a heat shield between the exhaust and the floor of the Jeep? What temp is the hottest part of your exhaust? If you don't have one of those IR guns, maybe you can give us an idea where the carpet burned, and of course the answer to the shield question.

[rips millar]

melted at feet of rear passenger, no, didn't have a shield...
but lots of jeeps out there don't have shields and they are fine. gets very warm under passenger front seat and the glue smells every time I climb a slow gentle hill for even a mile....and that is with an existing shield, in fact a layer of .26 sheet metal and then an insulated cookie sheet(double wall) added to that, directly above the cat.
now I will admit that I am hyper sensitive to this now but through 2 heat shields the floor shouldn't be getting hot to the touch when its 45 degrees outside and I am not pushing any limits whatsoever, really....
also, when this occurs, you cant hold your hand in front of the exhaust, seriously too hot to hold it there for more than 2-3 secs.....

[Mudderoy]

Thanks. The only thing I can think of is restriction, I mean other than what Steve said about running lean.

Are you having loss of power at high RPMs?

[rips millar]

no loss of power at any rpms as far as I can tell.
a jeep with 33's aint no race car ya know.....I have a mini and a duramax and this car definitely lives in the slow lane comparatively.....
btw, just drove around for an hour trying to get it to get hot and nothing....seems to be running fine now(now) but thank you :patriot:

[Mudderoy]

no loss of power at any rpms as far as I can tell.
a jeep with 33's aint no race car ya know.....I have a mini and a duramax and this car definitely lives in the slow lane comparatively.....
btw, just drove around for an hour trying to get it to get hot and nothing....seems to be running fine now(now) but thank you :patriot:

Yep, when I had a problem with the catalytic converter (muffler shop told me it was fine too) I had no acceleration above 4k rpm. I broke all the welds and broke apart the cat from the muffler, and cat from down pipe. Cat was broken inside. I replaced cat and muffler, and this time used U clamps so I could fix it myself next time.

I hate just blinding trusting a shop that either doesn't know what the hell they are talking about or just plain lying.

Oh Amazon sells a back pressure gauge as well, just screws into the down pipe O2 sensor hole.

You were probably running lean. Hmmm I can't see what year XJ you have while posting, but if you have a 97+ and OBDII you can watch the ECU information live using a $15 bluetooth OBDII nub and the Torque app for a smart phone. Free version and $1.99. You can even watch the O2 in graphs. Might help you in the future.

[bruggz351]

melted at feet of rear passenger, no, didn't have a shield...
but lots of jeeps out there don't have shields and they are fine. gets very warm under passenger front seat and the glue smells every time I climb a slow gentle hill for even a mile....and that is with an existing shield, in fact a layer of .26 sheet metal and then an insulated cookie sheet(double wall) added to that, directly above the cat.
now I will admit that I am hyper sensitive to this now but through 2 heat shields the floor shouldn't be getting hot to the touch when its 45 degrees outside and I am not pushing any limits whatsoever, really....
also, when this occurs, you cant hold your hand in front of the exhaust, seriously too hot to hold it there for more than 2-3 secs.....

I too had this happen. Same scenario. We got to the top of a sharp pinch and stopped for a rest with the group. we all got out to stretch our legs, and my son says ' the jeeps smokin'. I spun round to see smoke pouring out of the RHS rear window. :smiley-scared002:
We were only running with rubber mats at the time, and it was just goo, bubbling goo, all over the rear floor!! When asked how he hadn't noticed, my son answered, 'oh yeah, my thongs were melting to the floor, I just moved my feet onto the trans hump.' :wtf:
Anyhow, all that side of the floor is now a nasty shade of rust. Burnt bad.:mad:
I still haven't remedied it though. :o

[bruggz351]

Grave dig. I have an update. On this scenario. I have replaced my exhaust, from the cat back, with a 2 1/4" x 18" hotdog and new tailpipe pretty much straight through to the back. I'm running a upper shock mount relocator, so the over diff pipe had to be re-routed.
The floor doesn't get half as hot as it used to.

If I remember, I'll upload a pic or two.

Cheers..

Sent from my FRED

[bruggz351]

Grave dig. I have an update. On this scenario. I have replaced my exhaust, from the cat back, with a 2 1/4" x 18" hotdog and new tailpipe pretty much straight through to the back. I'm running a upper shock mount relocator, so the over diff pipe had to be re-routed.
The floor doesn't get half as hot as it used to.

If I remember, I'll upload a pic or two.

Cheers..

Sent from my FRED
http://images.tapatalk-cdn.com/15/07/20/a019e3356a283706cc72505b24c165d3.jpg
http://images.tapatalk-cdn.com/15/07/20/b8cc3de933cc0771830e360300ef90d8.jpg
http://images.tapatalk-cdn.com/15/07/20/3f8f894f5bd5af3ba2de553188c623fc.jpg

Sent from my FRED

[Carves]

When asked how he hadn't noticed, my son answered, 'oh yeah, my thongs were melting to the floor, I just moved my feet onto the trans hump.' :wtf:


... and the gubberment thinks that children should not get smacked .. :rolleyes:

:D:D


Your exhaust, "fix", is still working out OK ?

[bruggz351]

... and the gubberment thinks that children should not get smacked .. :rolleyes:

:D:D


Your exhaust, "fix", is still working out OK ?
Heh heh heh.....

Yeah, Carves. Developed a few pinholes in the welds, but otherwise, cooled it down considerably. [emoji106]

Sent from my FRED