jeep exhaust too hot.

[ipkyss]

Jeep specs are 98xj 4.0 ax-15, 140k miles, runs perfect, smooth.

The problem is the exhaust is way to hot. It was a stock exhaust with a 30 series flowmaster, 2.5" after the muffler. It was hot enough to melt the undercoating and start it on fire.

I figured the cat was bad. Started with a new 2.25" downpipe,new cat, to the 30 series flowmaster. Replaced both o2 sensors. Same deal. Beating around the yard for 5 minutes and the cat and front of the muffler was glowing red.

Not sure where to start now. I would understand if it was not running right, but it runs perfect and just passed emissions today.

 

[buffalomatt350]

Even though it passed emissions, cats glow (and then melt and quit being effective) when they get loaded up with fuel. Make sure there is no reason that you'd have the engine dumping fuel out the exhaust, like that you have good plugs, wires, etc., also no exhaust leaks ahead of the front o2 sensor. If you have a cracked manifold, there's a possibility that air is getting into the exhaust and throwing off the first sensor's reading, making the PCM think you're running lean and then adding fuel. It could still have these issues even if it runs well and doesn't set a check engine light... Not sure what else off the top of my head. I'm sure the Flowmaster isn't helping the cause, but if you had it before without a problem, then nevermind that.

 

[ipkyss]

I have always had flowmasters on all my jeeps. The cat is brand new last night. I was thinking that was the problem and I was wrong. As far as I can tell, there are no cracks or leaks anywhere. o2 sensors are new this afternoon. recent new plugs, rotor, cap, wires. I tried all the basics.

 

[buffalomatt350]

Yeah, I have a flowmaster too, I was just throwin that out there..

I am out of ideas, other than I'd want to look further into the cat loaded up with fuel theory. Possibly somewhow get your hands on a scan tool with real time data readings (not the Autozone code reader) so you can look at the fuel trim and watch how the engine is responding to different conditions... Good luck.

 

[goodburbon]

Running too lean will cause the exhaust to get hot is what I was told. Sure enough I pulled my injectors and cycled the ignition a few times and a load of garbage came out of the fuel rail. Check your injectors and for trash in the fuel rail.

 

[doodahman]

My Flowmaster got so hot it melted my carpet. I moved it away from the body and installed a heat shield. No more problem. Flowmasters get hot and people tend to mount them too close to the floorboard. Cats are usually shielded pretty good.

 

[ipkyss]

I have had the flowmaster burning the floor thing many times. Mainly from bending the exhaust on rocks. But like I said, When I say hot, I mean glowing red like you had a torch on it. I guess I will have to look into the injector/ fuel rail. About to give up and swap in a Ls1 I have here...