For some reason when I put an air filter on my truck and run the koer diagnostics it comes up with rich codes for bank 1 and 2. I thought it was the old dirty cold air intake. But tonight I hooked up the factory airbox with what looked to be a new filter. Didn't look dirty at all. White fram filter. I got the rich codes again. When I remove air filter it runs great.
I've seen some things doing a search about the eec could be stuck in open loop. Maybe from the temperature sensor? Also saw if the eec thinks it's in WOT it will go to open loop. I was having a separate issue with my AC relay being tripped because the ecm is sending the WOT signal. I checked my TPS and values seemed normal between 1 and 5 volts as I open throttle. Could there be another thing triggering a WOT response? Should I try and restart the ecm? Disconnect battery?

 

So we are talking pre-1995 Ranger V6 with 2 O2 sensors

137 (R) Oxygen sensor not switching/system rich Left or Front HO2S
173 (R,M) Oxygen sensor not switching - system is or was rich - Single, Right or Rear HO2S

Rich codes means computer was seeing TOO MUCH weight of air from MAF or MAP sensor so its calculate open time for fuel injectors was too long
Or
Fuel pressure is over 45psi so too much fuel was flowing in when an injector was opened

Lean and Rich codes are all about injector open times
Say computer calculates 14.7 pounds of air came in from MAF sensor, so it opens injectors long enough to add 1 pound of gasoline, thats the 14.7:1 air fuel ratio the computer uses
Or 14.7 grams of air to 1 gram of gasoline
So lets say computer calculates each injectors open time as 100ms(milliseconds)
It opens the injectors for 100ms then looks at the O2 sensors
If there is not enough Oxygen in the exhaust thats a Rich burn
So computer lowers open time to 98ms, and checks O2s again
Then 96ms, then 94ms, then 92ms and so on until O2s show correct amount of oxygen, a good burn
If the calculated open time is off be 20% computer sets a Lean or Rich code, so in this example, 80ms sets Rich code, 120ms set Lean code

O2s can't work until they are above 650degF, so can't get Rich(or lean) code for first 3 or 4 minutes of run time, and thats when computer changes to Closed Loop, when O2s are warmed up enough to work
Thats what "closed loop" means, the fuel mix loop is now a complete circuit, a closed loop because computer now has feed back on its calculated fuel mix

Open loop means computer is running air/fuel mix from pre-programmed tables in memory, tables are based on RPM, throttle position, and air temp, it does this every time engine is started cold, or warm, its in open loop until O2 sensors start to work
And engine should run fine in open loop forever, you just don't get the best MPG as you would with Closed loop

O2s are heated, they need to be heated to work, i.e. 650degF, so they have a fuse both O2 share, in the cab or engine fuse box depends on the year but that should set another code if its blown

Now if you have a 1994 and older then computer may be at fault, pull it out and open it up, there are 3 capacitors that need to be replaced after 25 years, they are blue, also check all the diode, the black cylinders, may find a loose one

Yes the air filter thing is an oddity but don't see a cause/effect on that for the codes you get

Computer ignores O2 sensors at WOT on any year, because its not about fuel economy at WOT, its about the most power, its not technically "open loop"
Computer also ignores O2s at idle, idle is a richer mix to prevent engine from overheating at idle

 

Wonder if I should just replace the ECM? After I buy the capacitors and soldering iron kit it's like $45 a new ECM is $90.

 

I would look at it first

 

good point. I've just never saudered anything before. Idk if it's like welding? Looks alot more complicated. I saw a video looking at the 3 capacitors to see if they where swollen with black residue underneath. What would I check for on resistor?

 

I would ask around, maybe a friend has soldering stuff and would be willing to help out, its not that hard to do and parts are under $5
The Capacitors need to be replace regardless, if computer is out, 20 years is well past usable limit

Its the diodes that can get loose/bad solder joint, the part is not bad just needs to be re-soldered, they look like this: https://m.media-amazon.com/images/I/...ZL._SL500_.jpg

Picture of computer board here: Ford EEC-IV

You can see the 3 blue capacitors, they can be at different locations on yours, they are replace with Black ones, of same value, they last longer

And you can see the Black diodes all around the circuit board, just push on each to makes sure its not loose

Also just general look see for corrosion or dark areas from overheating, and check the 60 pin computer connector for corrosion

Replacement computer needs to match:
engine size
transmission type, manual or auto
EGR, yes or no

2wd or 4x4 doesn't matter