Check engine code 😖(intermittent)

[NCguy]

Truck is a 94 ranger XL, 4.0 AT 4x4.
I have a code (512) that comes on after reaching 45mph or above for a couple minutes. If I shut off engine and re-start code is gone everytime. Even though code clears everytime I restart engine I can still find codes 111&512 while key on engine off.
Engine running test says code 136. O2 sensor not switching and lean bank 2 sensor 1.

Things I've done to resolve.
Replaced bank 2 sensor 1 o2 sensor
Cleaned MAF
Cleaned throttle body
Replaced IAC
Replaced plugs & wires
Added lucas for injectors
Disconnected IAC while running and rpm did drop which I read means no vacuum leaks.?
Disconnected neg battery cable, pushed horn, turned on headlights to discharge any remaining power, waited twenty minutes and reconnected battery.
Still throws KOEO & KOER codes

Only thing I can ad is my truck came with a right and left o2 sensor and no downstream sensor from factory. The cat has been removed. Could back pressure be the issue?

 

[Otis413]

Replaced the fuel filter?? just a guess but maybe low fuel pressure (low volume) under load, might also be the filter on the gas tank pick-up.

 

[NCguy]

Replaced the fuel filter?? just a guess but maybe low fuel pressure (low volume) under load, might also be the filter on the gas tank pick-up.

Thanks I'll try that.

 

[NCguy]

Haven't tried the fuel filter yet but I did fix the code. I had a muffler shop remove and replace the o2 sensor. While looking at other things behind engine I noticed sensor plug didn't look right. I touched connector and it fell apart. After reconnecting it has had no code on in 25 miles.

 

[adsm08]

I assume you are thinking the code clears because the light is not on right away on restart.

OBDII will keep the light on until it is cleared. Yours does not do that. You have an OBDI system, where the light will be off after a key cycle until the fault is seen again.

 

[NCguy]

I assume you are thinking the code clears because the light is not on right away on restart.

OBDII will keep the light on until it is cleared. Yours does not do that. You have an OBDI system, where the light will be off after a key cycle until the fault is seen again.

Reason why I think it is cleared. Previously I could turn off engine, re start and code would disappear until I drove a couple miles above 40mph. Now I can drive any speed and no light comes back on. I've driven 70+ miles and 5-6 cycles with no light. Also, engine idles well and has better performance.

 

[adsm08]

Reason why I think it is cleared. Previously I could turn off engine, re start and code would disappear until I drove a couple miles above 40mph. Now I can drive any speed and no light comes back on. I've driven 70+ miles and 5-6 cycles with no light. Also, engine idles well and has better performance.

Oh, you probably fixed it, but most basic EEC-IV readers don't pull memory codes.