@charlos Many of the videos deal with vehicles other than Ford Ranger. The information regarding the testing of the parts is applicable to all vehicles and worth the time to watch.
Ditto what
@Blmpkn noted above. Test the catalytic converter pressure by removing the O2 sensor. Auto Parts Stores often loan or rent these gauges and tools. You will need to remove the O2 sensor, and the first video shows exactly how to do replace it on your engine. Great Videos here:
and here:
If the pressure is high going into the catalytic converter, remove it and clean it. You may be able to save yourself $200. Great video here:
If the pressure is normal (low) going into the catalytic converter, take a close look at the tail pipe and muffler. Check to see if the exhaust pipe or muffler is clogged with rust or crushed causing a high backpressure. Inspect and replace as required. Use an OEM specified muffler. Here's why:
If the catalytic converter IS clogged, next find out what is causing it to become clogged. If you have to replace the catalytic converter and do not first repair the cause of it clogging up, the new converter will also clog up.
Check to see if your PCV valve is worn out allowing excessive oil blow by. If you shake it and it the ball check valve inside is free, it is probably good. Check it closely for cracks and clogging. When in doubt, replace it for $10.
Great Video here:
and Another Great Video here:
Check to see if the EGR Valve is stuck. If so, clean it. Great video here:
Shop said compression is fine; did they perform both a Dry and Wet Compression test to check for worn rings? You may have thirty year-old pistons pumping excessive oil blow by into the exhaust manifold and clogging the catalytic converter.
Great video here:
Clean the Catalytic Converter Great video here:
Clogged Fuel Filter causing poor fuel pressure? Change the filter, inspect the fuel line for leaks and/or pinched areas. Replace any rubber Fuel Hose as they deteriorate and clog up. Be sure to use Fuel Line Hose, not vacuum hose.
Great Video here:
Now check the fuel pressure. READ THESE FIRST:
Part 2 -How to Test the Fuel Pump (1990-1997 2.3L Ford). (troubleshootmyvehicle.com) and Great thread noted from last year - very informative:
(2) 2.3L ('83-'97) - 1995 Ranger 2.3 manual trans fuel pressure question. | The Ranger Station Fuel pressure specific to your engine: The 2.3L SOHC (1989 - 1997)
Fuel Pressure 30 - 40 psi noted here:
Ford Ranger 4-Cylinder Engines - The Ranger Station
Great videos here:
and here:
Find the 1991 Aerostar Explorer Ranger Truck Shop Manual on ebay here:
1991 Ford Aerostar Explorer Ranger 2 Book Set Factory Shop Truck Shop Manual SK4 | eBay Very Reasonable - Make an offer.
These are tests you can do to find out why your catalytic converter is so hot and your engine is performing so poorly above idle speed. Many people have no idea about these other parts of the exhaust system.
NOTE: Lots of people sell customers catalytic converters they did not clean them or need and their vehicle still runs poorly. Hope this helps.