I have a 91 ranger xlt single cab short bed (4×4 2.9 5 speed) that ive been trying to fix up for my son off and on for the past 2yrs now but i am totally stumped, it is running extremely rich to the point that it is fouling plugs and smoking like a dragon, i have replaced every sensor that has anything to so with the rich/lean fuel and then some but nothing has helped and im out of ideas, here is a list of things i have replaced so far....
main computer (located in the passenger side kick panel)
O2 sensor
New fuel injectors
New Distributor/w ignition mod and cap
spark plugs and wires
Idle air control valve
Map sensor
fuel pump and filter
throttle position sensor
intake air temp sensor
engine coolant temp sensor (the sensor for the computer not the gage)
and probably a couple more things i am forgetting! Does anyone know what could be going on with this truck? The only thing I haven't changed is the fuel pressure regulator but the fuel pressure is steady at 40 psi and holds fuel pressure for several hours after the truck is turned off, there is no gas in the vacuum line that runs to the fp regulator and i cant find any vacuum leaks! Any advice or ideas will be appreciated, thanks in advance!

 

Pull out the computer and change the 2 or 3 barrel type capacitors

Blues ones seen here: Ford EEC-IV

1991 2.9l will be slightly different layout and they can be black as well as blue color
The values on each one needs to be matched as well as the + and - orientation, so take pictures before removal
16uF 30V Capacitor can be replaced with 16uF 50V or 100V, but not lower V, and the 16uF must be exact match

Computer is the source, it interprets all the sensor data
So if its not doing its job then replacing sensors doesn't change anything
Also unplugging the 60-wire connector might show some corrosion inside, and since sensors only use 5volts even slight corrosion causes big issues

 

Thanks for the reply but i think i found my problem and its an obvious one, i bought new (rebuilt) fuel injectors and they were supposed to be for a 2.9 or 3.0, well they were a different color (yellow instead of grey) and after all my work and money spent i realize that they sent me the wrong injectors! They are for a 4.0 or a 5.0! That's why I think im having the blackened plugs and extreme rich issue, i feel like i should have caught the issue alot sooner like as soon as i received the new injectors, i ordered the correct injectors and will post whether they fix my issue or not. Thanks for the reply, if the injectors dont cure the problem i will try your solution.