Is there any reliable way to check if a catalytic converter is bad without removing it?
My XJ has started sounding like it has an exhaust leak when it first starts up in the morning. There are no obvious visible cracks in the manifold so I'm wondering if the cat is clogged and is causing excessive back pressure. It's got 103k on it so it may be bad, but I don't know how to check it.
-CT
Clap Trap did pass the time by typing:
with a vac gauge.
udaman! Thanks.
Clap Trap did pass the time by typing:
np.
I should say that exhaust cracks are damn hard to find. My header split on the ZJ and it did like your talking, noise till it heats up and seals again. Eventually if it's the header, folks will think your driving a diesel.
My header cracked between the two pipes, just in front of the collector. (the last Y) The only way to find that crack was to start the engine cold and feel for exhaust. (you don't have much time to do this before it gets bloody hot.)
One ol-timer gave me another way. Stick a vacuum cleaner on the tailpipe then wave a cigarette (smoke source) around the pipes. your looking for where stuff gets sucked in.
I use a pressure guage that screws into the O2 sensor hole and the guage mounts on the wiper arm so i can see it. Pressure measurement while not driving is worthless.. It always throws a code, but thats ok.
Initially, I thought it might be a crack in the header like you're talking. But I tried putting a hand in and feeling for leaks. I've done that on my old CJ a few times and found leaks every time. But I didn't feel anything on the XJ. I can usually hear where the leak is too, but no luck with that on the XJ either.
I was actually hoping it would be a cat problem that was causing the joint between the header and exhaust pipe to open slightly. But really, since it goes away after a few minutes, it's probably not a cat problem and is more likely a small crack somewhere that I just can't feel. A cat would be easier to fix. If it's a manifold leak, I'll just wait till it starts spewing fumes before I touch it.
SWMBO probably wouldn't let me hook the vac up to the tailpipe - might get it dirty ya know. Otherwise, I'd give that a try.
Ya know what else is odd, but it came like that from the factory, is that the exhaust pipe has a serious crimp in it right where it makes the turn leaving the engine bay. It's crimped to about half diameter. My cousin has an XJ that's the same way. Very strange.
Clap Trap did pass the time by typing:
They all do. I've head everything from "it's how the machine bends them" to "it's some sort of noise abatement/horse power robbing thing" Even my downpipe had that crimp. That's why I had a local muffler shop bend me up a new one when I put a higher flow cat on.
Personally I belive it's a cheap ass bend. Since forming a constant diameter bend requires skill and pressing a dimple bend is easy for a machine to do.
I use a chunk of hose and hold it to my ear then around the exhaust to listen for leaks. It works pretty well. Shops use an open stethoscope. Our local parts stores sell them cheap.
It wouldn't hurt anything to put a torque wrench on the manifold bolts. They are known to come loose now and then....
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: N>MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.