Air to fuel ratio problem?

Hello, what are you referring to when you say 16.1 17.1? Is your scan tool giving you an air fuel ratio number? and you're getting an oxygen sensor code? What code are you getting?

The numbers are coming from my air fuel ratio gauge and yes it was the downstream 02 sensor, I replaced it with no luck still running very lean I can’t remember what the exact code was I’m going to have them run again tomorrow.

Okay. So, now you have an Acura engine in it, it looks like all the 2000 Integra's have a 1.8-liter dual overhead cam, is it a VTEC engine? I just want to make sure I'm looking at the correct wiring diagrams. And was any work done to the engine before it was installed?
It's possible you're still getting the rear oxygen sensor code because the oxygen sensor heater circuit is not working. The 1st diagram shows the rear oxygen sensor wiring, the heater circuit will be the 2 wires at the sensor that are the same color. There should be 12volts going across those 2 wires. In the 2nd picture is where the wiring harness for that sensor runs up into the body and there is supposed to be a rubber grommet there to prevent the wires from rubbing through the insolation and shorting out, it was common on these for people to leave the grommet either out or push it up. If the wires are making contact on the body at that point, normal vibrations cause the wires to end up being cut or shorting out on the body (frame) of the vehicle. Ill post the fuse also that powers the heater circuit, But the sensor will not work without the heater circuit functioning. The engine computer might also monitor that circuit to verify it is working by monitoring either current flow or voltage. So, check that the wiring at that grommet is not shorted out.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

https://www.2carpros.com/articles/how-to-use-a-voltmeter

It doesn’t say VTEC, so I’d say not I personally didn’t build it previous owner did, but Ik it has Nippon rods and piston. Brian Crower, Cam valves springs skunk2 rockers, Solid Motor mounts so shakes a little when sitting at a light. Had a boosted D in it and still has ATF, boost, oil pressure, volts and water gauges that are hooked up and working, Stainless headers with full exhaust. The only thing that doesn’t work is PS. That’s what he sent me and tbh idk what “Had a boosted D in it still has ATF, boost,” means because how can you remove the boost but still have it?

Okay, look up at my last post, refresh this page. I put the wiring diagram and what to check on the rear oxygen sensor. Here is some additional information. Once you get the rear Oxygen sensor issue taken care of, and if you still have an issue with a lean condition, you will most likely get a lean code. I'm not sure how accurate the air fuel ratio gauges are. Scan tool live data would give you a much better idea of what the engine computer is doing with its fuel strategy.

Does the vehicle have a turbo? Sounds like the vehicle the engine came out of had a lot of modifications and the gauges for all of it are still hooked up and functioning. ATF type D is a high-grade automatic transmission fluid. So maybe that's what he was referring to.
It's difficult to tell with vehicles that have been modified so much and then taken apart. Who knows what's left and what's not.