I have a 95 firebird with an lt1. It has a cam and headers and ran fine when I put the cam in about a year ago. Lately Ive noticed when I accelerate real hard dark smoke comes out the exhaust. Its not black but its not white either. I checked the coolant and oil to see if it was burning either and they were both fine.

I have an air fuel gauge and it is just bouncing back and forth from lean to rich. I also have TTS Datamaster and it said my o2 sensors were putting out 60mv at the lowest point and 900mv at the highest point and it would do that really fast.

I thought it might be a bad o2 sensor but I just replaced one about a month ago and the other one about a year ago and both o2 sensor are reading the same.

Could old spark plugs and wires cause this?

If not what else could cause this?

 

A 02 sensor can cause a car to run crazy rich. I had the same issue a few weeks back on my TA. I would replace both of them at the same time. I learned the hard way after replacing one two months latter the other one gave out.

 

And isn't a sign of O2's going bad that they'll bounce around really quick like that? They're supposed to have a constant reading, right?

 

The upstream O2 sensors are supposed to jump from rich to lean and back at a fast rate, A steady reading indicates that the sensor is bad. The downstream sensors, if present, will show less variations because the cats clean out the exhaust. Also, the PCM does not look at the O2 sensors at WOT, so if your car is belching black smoke at full throttle, it is probably the result of misfire or a FI problem.

 

It would also be a smart idea to clean or replace your plugs once you replace the sensors if it has been running that rich its put a hurting on them.

 

Ill probably try to replace the plugs and wires since that hasn't been done in a while and see what that does.

Could bad seals around the fuel injectors cause that too? I know on a few of them they are starting to deteriorate.