Looking at your freeze frame data above from your scantool, it seems to me that the Bank 2 O2 sensor may be lazy.

Look at the idle short term fuel trim & the bank 2 O2 sensor reading.
Then look at the data at the 66 mph speed, it seems to have sorta caught up.

So I might suspect a lazy O2 sensor on bank 2.

 

As was noted above, the fuel pressure regulator on your '99 is in the fuel tank along with the fuel pump assembly. So you probably disconnected the fuel pulse damper, which Ford describes as follows:

"Located on the fuel rail is a pulse damper. The pulse damper reduces fuel system noise caused by the pulsing of the fuel injectors. The vacuum port located on the damper is connected to manifold vacuum to avoid fuel spillage in the event the pulse damper diaphragm were to rupture (the pulse damper should not be confused with a fuel pressure regulator)."

Also, the fuel pressure on your '99 is supposed to remain constant at 64psi (+/- 8psi) regardless of engine load or other factors. That's how it's designed.

However, you could be right about the fuel pressure drop when you disconnected the pulse damper. "Constant" fuel pressure means just that. As such, maybe the pressure is not supposed to drop (as you've theorized) if the damper is removed. So what you have described could still very well be a valuable troubleshooting technique with regard to Ford Ranger mechanical returnless fuel system. In any event, it led you directly to the source of your problem, and nobody can argue with those results.

Nice job and good post.

 

Thank you for the clarification. My apologizes for the mis-information. And yes. It did lead me to the source. The unfortunate problem I had was that it wasnt throwing a code and I drove for many months before trouble shooting that problem. Even had it into the Ford Garage 4 different times and no-one could tell me what was wrong. One thing I learned from this was, if you have a problem do not take it to the dealership, if there is no code their mechanics wont do a thing for you. Do it yourself or find a good old school mechanic.

 

Thanks for your response.
I will select only bank 1 and bank 2 sensors and test drive again. That will give me more history to compare. If the trend is consistent, it may be an answer.
I have avoided just replaceing parts, I think that's too common today and also too costly. I acquired this truck due to a death in the family. A dealership was unable to repare it after three attempts. It has been a challenge and I intend to find the problem.
At this point, the confirmed bad parts are 1. a dead IAC 2. a questionable ECT 3. a bad (at times) MAF

Thanks again!!