1994 Ranger 4.0l, manual, 4x4, almost at 400k

I have been doing my own clutches for years, but I am getting older now and figured what the heck I will have a shop do it.
Local shop and I know them, price was a bit high and got higher(rear main seal and new Master), lol, but still what I considered reasonable for the work it takes.

So I picked up the truck and new clutch is great, chirps the tires
Driving home engine warms up and starts missing, and Check engine light(CEL) comes on
I have owned this truck for many years and many many miles and never had CEL come on.

Read the code, Rich on Bank 1, not switching, cleared code
I figured they had to drop the "Y" pipe to pull trans so forgot to hook up an O2 sensor on reassembly.
Checked, both O2s are hooked up

So checked the Fuel Pressure Regulator's vacuum hose, clean and dry.
Cleaned MAF
Check TPS connector and other connectors in engine bay, all clean and dry

Truck had cooled off by now and seem to run fine so I took it for a longer drive, warmed up and started missing and generally losing power, CEL came on again.
Pressed gas pedal down for Wide Open Throttle(WOT) and wow engine ran great, got all the power back, all cylinders firing.
Let off and back to low power and missing.

Got back home and check codes again, had 2 codes this time
Rich on Bank 1
Lean on Bank 2
LOL

I wonder..........................
When they reassembled the exhaust they had reversed the O2 sensors, got out the wiring diagram and there is only 1 wire different on each.
grey/blue passenger side(bank 1)
red/black drivers side(bank 2)

They were reversed, swapped the connectors around

Runs great now
When engine is cold O2 sensors are not used, Open Loop
When you are at WOT O2 sensors are ignored
This is why engine ran OK cold and at WOT

I did talk to the mechanic that did the work, before I found the problem, just to see if they had done anything in the engine bay while doing the clutch work.
He said no and engine was running fine for the test drive, which it would have been because engine was cold.

I did call him back to let him know about what had happened, he didn't think that could happen, connectors should be different, they aren't, which makes sense because when you buy an O2 sensor there is no left or right you just have different pigtail wire lengths, so connectors would have to be the same, at least in '94

 

I would have never figured that out! LOL

 

It's good it wasn't someone that didn't know, you can imagine the headache for that person.

 

Well they wanted me to bring the truck back in so they could find out what the problem was.
I thought about it.

But they would have to take my word for it that the truck was running fine BEFORE I brought it in for the new clutch.
Not sure I would take MY word for it, lol, a 1994 with 400k on it

So I didn't take it back, I knew it was running fine before so it couldn't be too many things that could go wrong.
I know famous last words, lol.

Got lucky I guess, simple fix