KOER 41 & 91 won't go away after changing O2 sensors

[DragTriper]

Hi Guys.

I'm getting a little bit frustrated trying to solve this.

I got an 89 5.0 liter and I have codes 41 & 91 (No HEGO switching detected always lean (right side).& HEGO sensor circuit indicates system lean (left side)). I changed both O2 sensors and the car is running much better with more power but I got both codes on KOER test again after clearing the codes.

The car seems to run fine tho (Idles a little erratic for a few seconds on first start up but idles pretty smooth after) .

1. Why are my sensors detecting system lean? (what is triggering this code?)
2. Besides O2 sensors that I changed what else could be malfunctioning and making my system lean and causing the computer to add more fuel to the mixture making it run rich?
3. What does No Switching in oxygen sensors mean?

Note: I used to have the thermactor air injection system inoperative code (44 & 94) but after changing the O2 sensors I didn't get them.

I'm very confused. I appreciate any help.

 

[Haus]

Ive been dealing with this for a couple years. I think Ive given up on it lol

I did things like check for vac. leaks. Checking the voltage on the maf. Clean the Maf. Pull the vacuum off the regulator and plug the line so the FP is a little higher. change the O2's, change fuel filter, check the wires on the computer for the right voltage for the 02's, checked the ground for the HEGO's(should be an Orange wire connected to the fire wall coming out of the Fuel injection harness)

Now with the 44 and 94 if you dont have your smog pump you would get these or you can check for vac leaks there to start if you do have your pump. the codes may come back

Now im looking into the fuel pump or relay for my problem. I didnt have the codes for a little while then I noticed when I did get the 41/91 when I turned the key I didnt hear the fuel pump prime when I started it. So when I dont hear the pump prime, my car runs like crap. but when I do hear it prime, it runs great

 

[HISSIN50]

1/2. Haus' suggestions are good. As he said, look for something systemic like the MAF, a vac leak, fuel restriction, and so on.

3. The O2's toggle back and forth between lean and rich constantly (it's like if you removed the gutters on a bowling lane and put up walls instead. No matter where you bowled the ball, it would bounce off the walls and then hit most of the pins). If you're overly lean (at the rich adaptive limit), the O2 can peg low (low voltage = lean). The reading can stay pegged there if the stoichiometry doesn't get near the target. I would test the signal voltage with a DMM. You should see it bounce back and forth between 0.1 and 0.9 V at least once a second. Be sure the car is run for a couple minutes before testing them.

Good luck.