Exotic problem: rattle *inside* the cat converter, '05 XLT

[pkn]

Hi All,

Well, here it goes. Loud rattling sound from under the car, started overnight. I got under and looked - it comes from the left catalytic converter.

First I was hoping it's a piece of gravel or something, which got under the converter heat shield, but all my shaking, hitting, and careful listening with stethoscope convinced me that it rattles actually *inside* the converter.

And rattling does not change with vibrations change, only with change of RPM. Rattling occurs only at idle, all RPMs higher than 1000 quietens it completely. So it looks like the flow of exhaust gases moves the loose part around, causing rattle, but with higher RPM the exhaust flow pushes the loose piece in some corner and holds it there. Drop RPM below 1000 - and it rattles again.

Judging by the sound, it's a rather large piece of iron, maybe something similar 1/2" nut by size/weight.

The only hypothesis I could come up with is that the internal part of the front-left O2 sensor (it's located few inches above the converter) broke off and have fallen inside the converter. No, I did not yet read the codes to see if the sensor reports bad. But I know for sure (did emission inspection) that a week ago there were no codes.

So... so, my great plan is to unbolt the V-shaped part of the exhaust pipes (between the engine and the muffler) and shake out this little rattling jerk. Or fish it out with magnetic pickup, if I will be not able to take the whole V-pipe from under the car without too much of disassembling. And, of course, replace the broken O2 sensor if I'm right about it being broken.

Questions... heh, they've got to be rather stupid, but I gotta ask anyway. So, questions to the respected community:

Did anyone ever had similar problem? Or heard about it? )

Could there be another reason, different from broken O2 sensor?

Are all the three O2 sensors the same on 2005 Explorer XLT 6 Cylinders K 4.0L Flex Fuel SOHC?

Are there any underwater stones in unbolting the V-shaped exhaust pipe and taking it out of the car? I don't have a car lift, just jackstands.

Will the catalytic converter survive this mayhem, or I should replace it?

I have an inspection camera so I will probably be able to look inside the converter, but how do I judge if it's OK or badly damaged?

Many thanks in advance!

 

[swetrid]

The catalyst itself breaks apart and causes the noise. You will need new cat, eventually light will come on giving you cat efficiency codes.

 

[pkn]

Thank you, swetrid!

I've just got back from O'Reyllies, scanned the codes - there are no DTCs in the computer, and the problem started 5 days and about 100 miles ago. I guess, this confirms that the O2 sensor is actually live and well, otherwise it gotta be in the codes by now. Therefore, your suggestion:

The catalyst itself breaks apart and causes the noise. You will need new cat, eventually light will come on giving you cat efficiency codes.

is probably true. Drat, I never thought the converter intestines might broke in such a noisy way!

Well, I think I will be replacing the whole V-pipe with both converters in it.

Might be slightly more expensive than cutting-out-and-welding-in just the left one, but will save me the trip to welders and definitely the hassle of reinstalling the pipe back after it was welded under wrong angle

 

[jayton]

I had a noise that I thought was rattling in the cats. Eventually the cats clogged up and I replaced the entire y-pipe with 3 new cats. The rattle did not disappear. Once I got under the vehicle with it on jack stands and running, I then could tell that it was something inside the engine making the noise. It sounded like it was coming from the lower rear of the engine or inside the bellhousing. I see that you have the V6 and you said the noise changes with rpm, are you sure it is not the rear timing chain? Can you make a video or sound clip of it and post it to photobucket?

The mid-pipe is easy to remove. The transmission cross brace would need to be removed, which means safely holding up the transmission in place while you work. Heat shields and rubber hanger mounts are simple enough. PB blaster on the nuts that connect to the headers the night before makes it go a lot easier.

I've had hacked and welded exhaust before, and like you, I decided I dis not want to go that route. I wanted something that was direct fit and bolted in and out as needed. I was broke so I went with the cheapest I could find on rockauto.com and amazon. It was Eastern Catalytic. Let me warn you now, go ahead and spend the money and get the magnaflow. The one I got looked like a beginning welding lesson for a high school shop class where all the students got to take a turn. There are several leaks I have had to try to seal.

 

[pkn]

... I see that you have the V6 and you said the noise changes with rpm, are you sure it is not the rear timing chain?

Rear timing chain?! I did not know there is such thing...

About my rattling noise: yes, I'm pretty sure it comes from inside the left cat - I have been listening with a mechanic's stethoscope thru everything I could reach. It also changes with RPM in a way which definitely says that it's not a timing chain: with RPMs coming up the rattle does not come up and than gradually stops, as loose chain would sound, it stops abruptly. But most of all - I'm sure it's not coming from the engine or torgue converter or tranny, it's definitely located inside the cat converter.

Can you make a video or sound clip of it and post it to photobucket?

You will be laughing, but I'm so old school I don't even have a gadget to do this... digital camera I have doesn't make video, and my cell phone is Nokia 1100 if you can believe it..

The mid-pipe is easy to remove. The transmission cross brace would need to be removed, which means safely holding up the transmission in place while you work. ...

Thank you - that's exactly what I hoped to hear!

I went with the cheapest I could find on rockauto.com and amazon. It was Eastern Catalytic. Let me warn you now, go ahead and spend the money and get the magnaflow. The one I got looked like a beginning welding lesson for a high school shop class where all the students got to take a turn. There are several leaks I have had to try to seal.

Thank you very much again. Very useful suggestion which I'll definitely follow!

 

[pkn]

OK, just to report back to the community.

In full compliance with the swetrid's prediction, few month later the "check engine light" came up. The code was P0430, which means "Catalyst efficiency below threshold (Bank 2)". The noise was gone (gradually stopped) by that time.

Car was not used much, so I did not hurry, but now (a year later) it is time for inspection again, so I started acting.

I bought full Y-pipe replacement kit with both cats, Magnaflow 49406, which supposed to be a direct bolt-in replacement. After about an hour spent under the car I realized that there is no way for me to reach one of the nuts on passenger side of exhaust manifold without too much trouble. So I gave up and drove to a muffler shop.

An hour and $70 later the replacement was installed. The Magnaflow 49406 turned out to be NOT a direct fit for 2005 Explorer XLT: bolt holes spacing on flanges were slightly different, so they had to expand the holes, and there was something wrong with angle of exhaust pipe approaching manifold - it was leaking there, so they had to cut, readjust, weld it back, etc.. So much for "direct fit" from Magnaflow.

Anyway, the replacement is done and I hope the "check engine" light will be gone.

One interesting thing the mufflers guy told me is that the car (2005 Ford Explorer XLT 65 kmiles) should still have manufacturer warranty, he mentioned it be 8 years or 80K. Funny thing the seller who sold me this car actually worked at a dealership, but he never said anything about warranty. If it's true... well, then I've paid for the pipes and cats and work because of my stupidity. Not the first time, not the last...