Poor gas milage and blows black smoke

Should an O2 sensor make a check engine light come on? There is no check engine light on anywhere. Doesn't the sea foam clean the injectors or no?

I have a 1995 Chevy an it was doing the same thing I replaced the PCV an the o2 sensor an it fix it

For example, if the valve clogs, or gets stuck in the closed position, you'll notice one or more of these symptoms: Increase in internal engine pressure. Failure of one or more oil seals or gaskets. Engine oil leaks. Moisture and sludge buildup inside the engine. Engine surges and possibly black smoke

Ok, I will try that. Thank you gentlemen!

That example is for the PCV hopefully it works for you I know the PCV only cost me $3

Yes sir that sounds exactly like it! It is leaking oil , black smoke and surging. So just change those 2 and that should fix it. Thank you very much!

And yes if your o2 sensor is out or bad it will make the engine light come on some times not right away it could come on after driving a few miles down the road i know mine wouldn't come on right away it had to be warmed up or driven

I've put probably close to 1000 miles on it and it has never came on. I am going to start with the pcv valve and see if that does it. From your description, I believe it will take care of it. Once again, Thank you very much!

This will also help with the poor gas mileage, correct?

Yes I believe it will I had the same problem with my gas mileage what I ended up doing was I replace the PCV valve and I replace the map sensor and I replace the engine temperature sensor and I replace the ignition coil in that helped out on my fuel mileage a lot I know it's a lot to replace but it's an old truck and it's better if you just go ahead and replace it then let it go out but if you dont want to replace all them at once I would start with the MAP sensor

Bad MAP sensor symptoms: Rich air-fuel ratio. Lean air-fuel ratio. Surging. Poor fuel economy. No-start condition. Lack of engine power. Stalling. Detonation and misfire.