Dave

I have a 1989 740 that developed a rattle in February 2000. The catalytic converter was replaced (welded) in 1997 by Midas (for a prior owner) at a cost of less than $200. My shop does not work on welded exhausts. They said my only choice was to go back and get a new catalytic converter welded in or they could replace the entire exhaust (exhaust pipe/catalytic converter/muffler/etal) for $1,000. They sell a compatible catalytic converter for about %300.00, but do no welding.

I have read the brickboard with interest on this subject for some time and asked my shop about just going with the rattle. My shop said most likely a part of the catalytic converter had come loose, was rattling and would eventually break free and might plug up the exhaust, possibly in the muffler. My car might stop running if that happened. It might also mean replacing a still serviceable muffler. I have watched my car for 9 months now. Mileage may be down a tad but barely noticeable. Power and performance seems about the same and I noticed no overheating, even during 100 degree summer days. The rattle has become less noticeable or at least I notice it less. I believe it is not nearly as noticeable. I know what I need to do is replace the catalytic converter at a shop that will weld in a replacement, but I entertain thoughts of getting a catalytic converter and trying to replace it myself without welding to try to salvage the rest of the exhaust for later replacements of parts of the exhaust system without welding. Three years for a catalytic converter is not very long. In the past I have gone with Vovlo mufflers and pipes because they lasted much longer for me than the cheaper alternatives. I had a 1980 240 for 17 years and never replaced the catalytic converter. It may have needed replacing but it just never became an issue.

Others on the brickboard have noted that sometimes a nut or a cover to a sensor can come loose and lodge in the catalytic converter. I do not know how to determine what is causing the rattle and if such matters make a difference as far as seriousness of the problem. My problem sounds to me like a part of the honeycomb of the catalytic converter came loose but I am not sure.

I do not have the answer on how to best proceed, I am still reading the brickboard for ideas and experiences. I hope my comments are of some assistance.

Jim Weber