truck running like crap

[ranger]

My truck when it is cool runs fine for about the first 15 miles then from a little bit of throttle to about half it runs real rough and black smoke comes out of the pipe then after half throttle it runs normal. Fuel filter was just changed plugs were changed and they are black again air filter is clean. Can't figure it out?

 

[adsm08]

I'd start with the oxygen sensor.

 

[ranger]

Is there a way I can test the o2 sensor to see if it is bad without buying a new one?

 

[Bondo]

My 87 Ranger that had similar issues had a bad FPR.

Just something else to consider.