1995 Mustang Problem Child

[TMAN1970]

have 95 mustang that thinks it is running lean. smoke tested and fixed all vacuum leaks, fuel pressure test is good and fuel volume is good. o2 reading staying way down at 20 and not switching unless you give it gas. originally suspected maf sensor and replaced with napa part. still can unplug maf and it runs good but o2 stay high and of course check engine light on. did replace 1 o2 sensor cause of it sticking on 0 and now at 20 with other. blocked egr port and same result. 1 thing i am uncertain of is i am showing a volt ref. of 6.3 a little high but enough to cause a problem? drilled hole in exhaust below o2 to see if cats bad but no change in readings

 

[Pantera2013]

There's a box that is underneath car idk if it's for later models or not but it can cause the engine light to come on. It's like a box or a cylinder and it cleans out air i believe and its black color.