misses and black smoke

scan for codes A and B on diagnostic link below left side of steering column. then check fuel pressure with a gauge auto parts rent it. See link on where to connect. should be 41-47 psi it may be a regulator for fuel. get back to us with codes I do not think it is a sensor.
https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

it came up code 13 , which is a 02 sensor ...correct ? but it doesn't say which one , there is more than one isn't there ?

oops it also came up with code 31 and 13

and can you tell me exactly where these sensors are located please

the older models may only have one and it will be in front of converter. code 31 is a park /neutral switch which could be a bad switch or a short. it's located under shift lever on transmission

was NOT the fuel regulator , we replaced it , the psi was 35 and still is.....where is the air/fuel sensor located , that's probably it cause its over $ 200 , just my luck , we haven't replaced the 2 sensors that showed the code 31 and 13 yet....don't know where to go from here

in my first reply I stated what the fuel pressure should be if not at minimum you have a bad fuel pump. code 13 is O2 sensor item b in pic and other is neutral switch item N4 in pic those are what your two codes are saying is wrong with car as well as you have a bad fuel pump. pump pressure should be checked with key on only.
https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

doesn't the black smoke mean the fuel is too rich ? how can it be too rich if the fuel pump is bad ?

first your very first question was a misfire and black smoke. because of the misfire which is low fuel pressure is one of the causes can cause black smoke and the O2 sensor reads the mixture which if bad the computer can't read it so it richens the mix up automatically so the car will run. however with low fuel pressure it gets all messed up because it doesn't have the right amount of pressure going into the injectors so it goes overboard. your fuel mileage has to be bad right now. also if there are any vacuum hoses broken/cracked/ or off will cause the same problem.

well after replacing the fuel regulator and filter and throttle pos sensor , no black smoke but car is missing bad and a loss of power , thinking about having it put on a scope , what does a scope tell you , and what wont a scope tell you and will it tell you EXACTLY where the problem is

you really need to scan for codes scoping doesn't do a lot unless there is a real problem it will show which cylinder is firing an d some other tests that are way to lengthy to explain. why don'tyou do a compression test an d get back with the readings. but if a 20% variance there is something wrong with that cylinder.