Originally Posted by
oj88
Simply put, black smoke simply means there's more fuel and/or not enough air was available upon combustion.
In addition to abiding to the prescribed PMS, there are a couple of other things that's not in the manual that I think should be given some attention, especially for high-mileage vehicles.
1. EGR valve condition and operation
2. Fuel injector wear, malfunction or leak
If an EGR is stuck open due to soot buildup or malfunctio, too much exhaust gas is displacing O2 and making the air/fuel mixture lean. On injector wear, if a leak is present or if the nozzle holes are worn out (have gotten bigger), the amount of fuel might be too much for the available O2 in the mixture. Then you have black smoke.