[KeithO]

My wife's car (1995 BMW 525i) has been slowly losing power and having reduced fuel economy over the last 18 months. I rarely drive the car. 2 years ago, it got about 32mpg on highway trips. Yesterday, I drove it for about 150 miles and only got 25-26mph.

It is down on power and very occasionally smells like a morning-after Guiness-fart. I am 90% sure that the cat is shot. I priced OEM replacement cats and every source I checked was in the $485-$500 range (yikes!). There is also the obvious choice of getting a universal cat and making it fit...

How can I be absolutely sure that this cat is bad? I'd like to be completely sure before I commit the time and potential effort on this.

Thanks

[y5e06]

Yes, a bad converter can also cause a vehicle to run hotter. I had one go bad, I didn't notice much in normal driving performance or temp wise. However, after a 15 minute session of giving the car a good flogging the temperature skyrocketed. tapped a whole before the cat in the y-pipe and the backpressure was very high. Those numbers should be spec'd in the service manual. If the car was post '95 then your O2 sensors after the cat could have been used to check abnormal readings. Possible BMW's had post cat O2's for '95?. Any kind of software to scan it?
I've gotten into the habit now of scanning all my cars when they run well and then saving the file for later to compare for when something doesn't run right.