My 1996 Celica GT runs rich. Please help!!, Otherwise the car runs great. Options

[JohanFer]

Hi everyone, I write to see if I can get some insight into what could be wrong with my car. I bought a BlueDriver scanner to see how then engine behaves and get information from the computer, get 0 to 60 data, and learn more from the data the car spits out, I am a scientist and am crazy about data handling. Anyway, I noticed that the short term fuel trim (STFT) goes negative, making the Long Term Fuel Trim (LTFT) push it to the negative limit of -14%. I have learnt what it means and realize that the car is running rich and therefore the computer is trying to compensate. The thing is that I don't know what could be wrong.

I was told that the problem could be an exhaust leak, since the car had some work on the engine head for it had overheated, this was also supported by a light click-clak sound when the engine was cold at idle and by a small cloud of white smoke when the car was started. So when I took it to the mechanic, he replaced the seals with new ones and brushed the exhaust manifold to clear the leak. The sound is gone, but I still get a now smaller cloud of white smoke when I start the car in the morning and after it has been off for a few hours. The car continues to run rich and I don't know what it could be. I get about 24 MPG and drive conservative.

Any ideas on what it could be? Are the any test I can do to check for possible problems. I know the O2 sensors work fine, since the voltages work as expected. Please help!!!

Oh, and I have a somewhat unrelated question: Is the 3SGTE engine OBDI or OBDII?

Thanks.

[Box]

Weak spark could cause an issue, leaking injectors could cause an issue, too high fuel pressure can cause an issue. The engine losing compression will cause a decrease in efficiency. There are many things that will just need gone through to find it. I would start with a compression check and then checking spark and the fuel pressure after the pressure regulator. Get someone to start the car with you behind it in the morning or after it's been sitting to see what the smoke is, it could be the injectors are leaking and the puff of smoke is fuel. If you've ever had it be hard to start and opening the throttle helped that would indicate such. Generally water is white, oil is blue, and fuel is black. Though it's been more in my experience that fuel is grey as for it to be black it'd be running like complete ****.

The Japanese market engines are JOBD, so technically neither.