In Reply to: 535 Running Rough and Rich posted by Jeff on September 26, 2001 at 11:22:02:
A buzzing fuel pump is normal. You have already eliminated the normal stuff. I am surprised there was no diagnostic indication of a rich air/fuel mixture, especially with a new O2 sensor. My best guess would be an air intake leak, or poor combustion in the chamber. When was the last time you cleaned the carbon out of the head with Techron or something? Poor combustion will also cause a sooty exhaust. Where the plugs fouled or sooty when you replaced them?
My '89 535 is difficult to start at first. Then when it starts it runs rough and I can smell gas. Then the idle will even out. But then after idling fine for about 2 minutes it starts to run rough again and I there is a "rich" smell coming from the exhaust and you can see that the tailpipes are blackend. Here is what I have done so far to try and fix the problem:
1. Installed the inline "check valve" at the fuel pump.
2. New oxygen sensor
3. New exhaust
4. New Plug wires, Cap and rotor.
5. New Coolant temp switch
6. New Spark Plugs
7. Six new Injectors and O-Rings.
8. Cleaned Idle Control valve.
9 Check computer and no fault codes are stored.
Could it possibly be the fuel pump, idle control valve or fuel pressure regulator? The pump does make a loud buzzing noise, but I cannot see how that could make things run rich. Any help anyone can give me would be much appreciated! Thanks!