Alright ladies and gents I have a 1993 3.9l that is running really rich. Looking for causes such as MAP sensor, intake manifold temp sensor, O² sensor, coolant temp sensor. No engine light, but does occasionally run rough, but shutting down and restarting clears it up. Looking for most likely culprit and work down from there.

 

How old are the O2 sensors? They have the most control of mixture. If they are original, replace 'em. (though you likely only have one.) NTK or denso sensors only please. These trucks don't play nice with others.

 

Agree with HY. Those O2 sensors can he tough to get off. My ‘93 has only one sensor. Soak it in PB Blaster days ahead of removing it. And a box wrench is mandatory and likely with a short cheater bar. You’ll have to cut wires to get the box wrench on the sensor. Not a lot of room to work but definitely doable.

Is your air filter clean?

 

I should add I have a 5.2L that has one O2 sensor. Have to think your 6 cyl has only one as well.