How do I change a catalytic converter on a 1991 Ford Ranger extra cab 4.0 engine

There is no such thing as a 2.3 Liter 8 Cyl. Ford Engine. You must be counting Spark Plug wires because the 4 Cyl engine has 2 Spark Plugs per Cylinder. I would check the Fuel Pressure first then if that is not the problem check the Catalytic Converter to see if it is plugged.

Try to cut off and use fitting to put together.

check for a clogged catalytic converter in the exhaust system...that will cause the symtoms u r having...have a repair shop do a back pressure test on the exhaust system in front of the catalytic converter if is is more than 3psi u have a clogged converter

I was looking for diagram for the serpentine belt for a1991 ford ranger
extra cab,four wheel drive, 4.0 liter engine but found out I had the wrong size belt. thank you anyway

You have 4 sensors, 2 on each exhaust side of the engine. 1 before and 1 after the catalytic converter. Hope this helps. 

Sounds like a catalytic converter shield is lose.

Look before and after the catalytic converters. They will have wiring connected to them.

its right under the driver door on the frame...

changed fuel filter lately? changed air cleaner lately?