Chevrolet Repair: 1991 Chev Lumina 3.1 eng excessive fuel, ohm meter, fuel comsumption

Question
When the engine temp reaches prox 140 to 160 degrees the fuel comsumption increases and when hot (prox 180) the black smoke boils out the exhaust and the engine wont run over 3000 rpm's. Runs good below this estimated temperature.

Thanks,
Ken  

Answer
Hi Ken,
If I had that car here, I would have a scan tool connected and be looking at all the sensor readings.
There are several sensors that send info to the ecm so it can decide how much fuel to dump into the engine, and there is obviously a mismatch there, and a scan tool, along with a good idea of what the readings should be, is required.
It should right off give you an oxygen sensor code saying the exhaust is rich, but that would not indicate a bad oxygen sensor, but rather one that is reading correctly, so don't jump to the conclusion that the o2 sensor is bad.
Most of the sensors can be checked with a good ohm meter, but a troubleshooting chart would be required.
So I think you might want to find a mechanic with that scan tool, who knows how to use it.
Van