Engine Performance problem
1998 BMW M3 6 cyl Two Wheel Drive Manual 152000 miles
Lately I have been having some strange issues with my car.
If my car sits over night, it never seems to have a problem starting up in the mornings. But usually when leaving school or work my car will take a few seconds to finally spark into life. I have changed the plugs and can't figure out what's going on. When the car does come to life after the cranks it will shoot some black smoke out of the exhaust.
The car runs just fine, I don't feel any power loss, but this worries me. Also, at high RPMs the car will shoot black smoke. I'm not sure if it's continuous or not because I'm afraid to keep my foot on the gas to find out. But it seems it is. I usually leave a good amount of black smoke after a downshift from 3rd to second into high RPMs.
The car is modified but it hasn't had this problem before and the car has been modified for over 4 years now.
Running on the rich side: Possible causes include a bad O2 sensor, excessive fuel pressure (bad fuel pressure regulator or plugged return line), leaky fuel injectors, dirty air filter or restricted air inlet, or a defective coolant sensor that prevents the engine management system from going into closed loop mode.