Ford F-250 XLT Longbed, 5.8L, RWD, GVR 8800. 240,000k miles carfax (although only 161,000 miles shows on instrument panel, I know the truck had work done but I do not know to what extent, as it was not done from the owners who had the truck before me).

Alrighty, my truck started to have a rather large problem of it spewing black exhaust out of the tailpipe, other than looking awesome it is causing a problem. I pulled my spark plugs and they were all horribly carbon fouled. Probably less than 12k on them. I have replaced the plugs but I know that is a temporary fix until they foul again. So I went and asked a mechanic friend of mine who swears that its a o2 sensor issue. Just to let you guys know I had switched over my exhaust system to the following, part no. 389-2020056, including 555-30480. Which I had failed to do my research on and features no downstream O2 sensors, which my truck had beforehand. Now my mechanic friend keeps saying that I have a upstream O2 sensor which is missing which is causing all the problems, however the exhaust system I have does feature a upstream o2 sensor port. For the life of me I cant find where my O2 sensor is for my truck upstream.

Now bare in mind that my "mechanic friend" is actually my teacher who is currently a certified mechanic who is teaching our college courses, and he has been doing so for over a decade. And he has even pulled up where it should be on alldata, but I cant find it. From the videos I have seen is that it should be hooked on to the starter, and there is nothing there other than the electrical wiring for the starter. Now I am in the midst of changing out the fuel pressure regulator which I believe to be the fault (already replaced the fuel pump).

So if anyone has any idea and or thoughts I would be very thankful.

 

This goes back a little but,
As I recall, there was only 1 oxygen sensor on those models. . It had OBD l system.

There were all kinds of TAB and TAD solenoids , AIR pump and diverter valves to help control emissions.
A stuck lean oxygen sensor (before the huge converter) or defective fuel pressure regulator could be causing the problem.
If you removed the vacuum hose from the fuel pressure regulator and fuel leaked out ,that was a sure sign the internal diaphram was ruptured and the regulator was faulty.