93 Z24 3.1 sooty black p[lugs, runs rough

[Mrwintr]

I have about given up on this car... It has acted like it had a skip most of the time, sometimes it would smooth out for a few seconds, but mostly runs rough. I have changed the plugs and wires, then the fuel injection rail with injectors, throttle body IAC, and TPS. Still running rough. Throwing no codes. Took plugs out yesterday and everyone of them was sooty black. Smells rich when running. I checked for vacuum leaks...none that I could find. Has 167,000 miles on it. Any ideas that I haven't already tried??

[OverAllComa]

Well, black and sooty means carbon deposits, but can be caused by a few things: Rich air/fuel, poor firing power, or even if you drive at really low RPM's for a long LONG time.

In any event, you should check the wires and coils. From there, consider investigating the Fuel Pressure Regulator. I actually just had to replace my FPR on my Twin Cam motor. It would drive fine occasionally, but stopping made it go nuts and there was the occasional miss at speed. Turns out cylinder 4 was VERY rich.

[Mrwintr]

Sorry, I forgot to say I had already changed the Fuel pressure regulator also, as well as the coils and plugs and wires. So any ideas from something I haven't already tried...?? Could the computer be screwed up or should I maybe check to see if someone may have installed one of those Superchips before I purchased it? If that was the case i would need to know where to locate the chip on this car.
I was wondering what could make the engine go to a default rich setting that doesn't throw a code....EGR maybe??

[wcamaddox]

Have you cahnged the o2 sensor? Also check to make sure the wire leading to the knock sensor isnt melted to the exhaust. If it does the ecm will think the motor is knocking and richen up the fuel/air mix. Happened on my 89 z-24 with the 2.8. The wire runs along the backside of the motor to the knock sensor and is really easy to get into the exhaust.