Posted by Chandler Ogden on January 27, 1999 at 22:28:56:
Hey-
I would appreciate a little diagnois/troubleshooting help...I was driving my '85 535i on a 200mile trip today, and had a wierd mechanical problem..
I drove the first 45 miles fast, with no problems. I then stopped, picked up a friend, and began the next leg of the trip. After a short while, at 65-70 mph, 2-3K rpm, the car stuttered and lost power. I reacted by downshifting and pumping the pedal a bit, and it cleared up and drove fine. Seemed like a slug of bad gas or something... This happened sporatically for the rest of the day, and each time, it would seem to clear up with more gas/higher rpm. It seemed to happen when the motor was more unloaded and at lower rpm, such as when I had backed off of the throttle and was just mainaining speed.
I filled 'er up last night, and thought I could have gotten some bad gas, so I added some fuel additive. This does not seem to have made a difference.
My initial guess was fuel filter or something wrong with the fuel pump. On further thought and consultation with a motor-head friend, I am thinking it may be a partially plugged catalytic convertor.
The car idles fine, and runs and accellerates OK otherwise.
Before I sink a bunch of cash into a catalytic convertor or into random part replacement, I am looking for opinions...
Any guesses on what the problem could be, or what a good troubleshooting approach would be?
Thanks!
Chandler