ive been having problems with my 22re running bad after warming up. it runs fine when its cold or when its warm and floored. as a test, i disconnected my o2 sensor. it runs perfectly now, except for the check engine light, and the fact its a little sluggish because im guessing its running rich to protect the engine. the check engine light was never on until i unplugged the oxygen sensor, so i im pretty sure i wouldnt have any codes until now. my question is, when a sensor is unplugged or not working properly and the computer senses it, does the computer just ignore that one sensor or does it ignore more than that when it goes into "safe mode"? cause if it only ignores the one sensor, ive found my problem.

 

When you stop will the truck miss so bad it'll stall?
If so, I think I may have found my problem too

 

as far as i know, the ecu doesn't know if a sensor is bad or not. it's just that the way things are designed, the lack of an O2 sensor means "run rich" the o2 sensor should be sending voltages oscillating around the 1v area (i forget the actual voltages, and i'm too lasy to look them up right now). low voltages mean "run richer" and high voltages mean "run leaner" so if the o2 sensor dies, it sends 0v, which the ecu interprets as "run richer" so if you're o2 sensor is bad and sending too high of a voltage (i guess it's possible) then you may be running too lean and that's why it's running like crap. so the computer really isn't "ignoring" a sensor. it's just interpreting the 0v from the unplugged sensor as a signal to go richer.

 

Actually... It depends on the ECU. Most ECUs _will_ know that the O2 sensor is missing.

An O2 sensor is spec'd to run within a voltage range, 0.2v (engine running lean) to 0.8v (engine running rich). This is by design so that the ECU can detect that the O2 sensor is missing (since the ECU wouldn't see anything from the sensor, which is different than reading 0.0v). ref: http://www.picotech.com/auto/lambda_sensor.html

The normal thing that an ECU will do when it's missing is throw a code. On a OBD II system, it'll be any/all of: ...and then it'll push the engine rich - since that's safer than running it lean.

Outside of the O2 sensor, the ECU will generally run an engine in some sort of "safe mode". e.g., if you're missing a knock sensor, the timing goes into full retard.