DIYwannabe

Howdy all.

This forum is much faster than benzworld. I posted there about "grumbling and puttering" in my ML320. I was under the truck tonight and found the seam in the second weld of the catalytic converter has failed. At high rpms, the exhaust blows out from about a 2.5 inch breach in the weld seam. This seems to be the only problem (No rattling from the inside). Can this be welded shut, and will that get rid of the grumbling/puttering?

Greg

DIYwannabe

I happened to stop at a muffler shop on the drive home. The guy there told me that the crack could not be welded without damaging the honeycomb inside. If this happens (he said) the rest of the exhaust could be dammaged.

Is it true that you can CAREFULLY re-weld the seam and not damage the insides? If so, what's the trick? I plan on going to the best welder in town tomorrow and ask him to help.

Thanks in advance,

Greg

mihir_d

Catalytic Converters are covered for 80,000 miles/8 years as per federal emissions law..

Mine were replaced by MB at 72K miles...under this fedral emissions warranty.

You should be able to get a replacement from MB if you are under that mileage..obviously your truck can't be more than 8 years old..

DIYwannabe

One more thing...
what does the rattling in the catalytic converter sound like? I may already be hearing what I thouht was valve clicking/engine knocking, but in fact is cc rattle....
Greg

DIYwannabe

101717 miles, oh well

mihir_d

Too bad..you are above 80K....

It started by a mild feeling that the engine noise had somehow increased.

Then, after a few days...it went from bad to worse...until...it reached a point where it was almost sounding like a steam engine firing under the hood rather than a gasoline one..

Finally, I could even smell the strange exhaust....

Now that you have discovered the problem with first CAT, You might also want to check your second CAT....it could be leaking too.

What year is your ML by the way? 2000 MLs had a faulty CAT installed from factory...they just cracked open from the weld...

Its $2400 to replace both....ouch!!!
It is under $500 to replace on any of the Japanese cars...

DIYwannabe

1999 the other one's not leaking... yet

mihir_d

I guess you are out of luck then...try a weld shop and see if they can help...I know, they do fix CATs on some Japanese and American cars...

My Mass Air Flow (MAF) sensor had a problem at 72K miles, the same time around the time the CATs blew....MB replaced the CATs, but not the MAF under the 80K warranty. They wanted $500 to replace it...I did a DIY clean up job on the MAF and its back up without giving any more problems..

If it comes to replacing the CAT, I suggest you look for it at non-MB shops mostly online...I am sure MB doesn't manufacture these CATS they contract it out to some vendor...the same product from the same vendor when purchased through a non-MB channel is significantly cheaper...

I too was considering purchasing my MAF (if it would have come to replacing it) from a non-MB shop..and was quoted as low as $250...against $500 by the dealership..

pointman

DIY, email sent.

DIYwannabe

I found a welder who put a quick weld on the bad seam and it worked! Purring like a kitten, and no rattle. 15 miles later, Check Engine light pops on. I take it to a code reader at autozone and the error/malfunction was reported on the oxygen sensor immediately before the repaired cat. I'm hoping that it's simply a discrepancy picked-up due to the change in flow through the cat as a result of the fix. I had it reset and will wait and see if it comes on again. Questions to anyone who has good answers:

If this sensor keeps throwing the check engine light, what do I do? Will I need to replace the Cats after all? Is anything being harmed, or might there be some dammage inside the cat that's restricting the flow? Any ideas?

Greg

mihir_d

My MAF problem had something similar...it was not until the CATs were replaced that the MAF problem became evident.

The MAF sensor had long gone bad, but the leaking CAT was making the ECU compensate for the faulty MAF sensor reading...MAF sensor by the way, also reads Oxygen content in the air similar to the Oxygen Sensors...except that the MAF comes prior to ignition..the O2 comes after the ignition.

It is quite possible that your O2 sensors went bad long back...but the leaking CAT made the ECU compensate for faulty O2 sensor readings...

Now that the CAT is fixed, the ECU is correctly reading the wrong O2 sensor readings and throwing the CEL ON.

Or, it could even be your MAF sensor...very much like what happened to me...my CEL came ON immediately after the CATs were replaced by MB...that made them check the whole circuit...and they nailed MAF as the culprit..

I did some research on this, and running with bad/leaky CATs for a while has some serious side effects. Yours could be just one of those..

DIYwannabe

Thanks for the last reply. I have been concerned about the MAF just because it seems to be something that often goes bad. I didn't put too many miles while the cat was leaking - 400-600 at most.

I have put 500 miles on the truck since fixing the leak and resetting the cel and it has been running great. The cel has not come back on and gas milage seems to be normal for this trip (23 mpg for the 500 mile trip - half hwy, half city). Noise is back to normal as well.

My next idea is to have the radiator, tranny and brake fluids flushed. Any thougths on these?

Thanks

Greg
ML320

mihir_d

Don't know about getting the radiator, tranny & brake fluid flushes on the ML...but I guess at 100K+ miles, it might be a good idea to do that.

The only experience I have with those flushes is on a 1995 Nissan Maxima that I recently bought used. It had 150K miles on it, and after buying, when I took it for inspection...my mechanic adviced me on getting the fluids flushed because of the mileage...

I did so, and yes, I can tell you, the braking, cooling and shifting had a noticable improvement.

mihir_d

Here's a site that sells the 98-99 Catalytic Converter (I don't which side, driver side or passenger side) for a reasonable price..

http://www.autopartsauthority.com/ca...320~parts.html