White smoke from exaust, heavy at first then light. bad smell, misses and no power,throws a p2196 code. replaced plugs, wires, coil, down stream o2, and mass air

You need to find a mechanic that is smart enough to use a scan tool that is able to view the live data stream and find the source of the issue. The P0420 code can be frustrating as it is usually something insignificant that sets it. Could be a vacuum leak, and exhaust leak, a bad wire to one of the O2 sensors. It takes time with a scan tool to nail down the cause.

This code refers to the upstream o2 sensor. The one between the engine and the catalytic converter. Use this link to test the o2 sensors, https://troubleshootmyvehicle.com/ford/4.0L/testing-the-oxygen-sensors-1.

Did you mass up wires? Could be bad wires? Bad plugs.

Illuminated Check Engine Lamp with Diagnostic Trouble ...

oemdtc.com/.../illuminated-check-engine-lamp-with-diagnostic-trouble-c...
May 11, 2015 - Illuminated Check Engine Lamp with Diagnostic Trouble Codes ...P2196, P2197, P0171, P0172, P0174, P0175 or P162F - 2015 Ford Transit.

P2097 Post Catalyst Fuel Trim System Too Rich
P2196 O2 Sensor Signal Stuck Rich
P2626 O2 Sensor Pumping Current Trim Circuit/Open
yeah, you really have a bad O2 sensor
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A bad injector also shake the pcv and see if you hear it
you should have been had a check engine light with those will turn on check engine light how old is the fuel filter

P2237 P2196 P2271 P0030 P0171

These are all O2 sensor trouble codes, except P0171 which is a fuel trim code,

You have a bad 02 sensor - up stream - Bank 1 Sensor 1.

Replace it, then road test. The engine computer has a 'default' fuel trim it uses when an O2 sensor fails so it can protect the catalytic converter. If this hasn't been going on too long, good chance simply replacing the O2 sensor will remedy your problem.

How about a fuel sample and new fuel filter? When the Service Engine light comes on this time, have you checked the final codes?

The throttle position sensor, TPS, could be bad with all the work done on the Butterfly flaps. No telling how many times its been removed and replaced. The black soot is a sign of unburned gas either through timing advance or too much fuel pressure for the situation. Thats the job of the TPS.

dirty air filter
bad plugs
low tire presure
bad plug wires
bad O2 sensor(major contributer)

Aftermarket parts can improve your feul economy ie: intake, exaust, plugs, wires, coil pack.

did the car over heat for long?
there could possibly be damage to your head like warping due to overheating and blowing a head gasket or something along those lines .
first check the oil dipstick is it milky?
then check the coolant is it oily?
and when it is running is it blowing any white smoke?
if you replaced the plugs and it is misfiring did you plug the wire all the way back on the plugs if not then the problem is a plug wire being loose and loosing connection with the plug.
sounds like a simple fix if you don't have water in your oil or white smoke coming out the exhaust.
troubleshooting it can be a bigger job but if you nail the right symptoms down you can corner the problem.
like if it is a coil pack or bad wire switch them with another one and see if the problem follows the wire or coil pack.for instance take the number one plug wire off and the number two wire off and put the number one wire on number two and see if the number one misfires. if so then the wire is the problem if not then try numbers three and four until you find out which cylinder is the culprit.
good luck and happy hunting.