Will the oxygen censor on a 1990toyota Camry keep it from fireing it's a2.0

Even a bad oxygen sensor couldn't keep the car from starting. It has probably lost spark or fuel to the engine. Listen for the fuel pump "whir" for 2 seconds with the key in on position, not start. Or have the fuel pressure checked, and scan for possible trouble codes. That is the place to start: scan, fuel pressure, check for spark.

behinde the exuest the first sensor after the engine *(sensor 1)

Sounds like you might need a valve job.

are there any codes ? does it back fire ?

PO171 OBD2 Code basically this means that an oxygen sensor in bank 1 has detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1. The P0171 is one of the more common trouble codes.

his code is triggered by the first downstream (front) O2 sensor. The sensor provides a reading of the air:fuel ratio leaving the engine's cylinders, and the vehicles powertrain/engine control module (PCM/ECM) uses that reading and adjusts to keep the engine running at that optimum ratio of 14.7:1. If something is not right and the PCM cannot maintain the 14.7:1 ratio, but rather there is too much air, it triggers this code.

this is the oxygen censors location, hope help....

Yes they can surely cause an misfire.

I cannot understand your statement "wich sensor is in bank 2"

If i am not wrong you are asking which sensor is present in bank 2 .

The 4th O2 sensor is located in bank 2

It may be a bad ignition mod,, Autozone test
are OK for batteries and Alternators but not
modules because it's not a real test, mostly
continuity test, not component heat test...
Get a new module and try it...

You would use an oxygen censor socket to repair that. You can buy one for pretty cheap or you can rent one from the parts house. You'll want to disconnect the electrical connection to the O2 censor, slip the socket over it (using the appropriate ratchet) and take it off. You can also use a 7/8 inch wrench on most cars if you can get it in there.

The thermostat will not harm the sensor, but the entire engine control system is designed to operate at 210 degrees, therefore all sensors will not recieve proper information,,,end result may be improper mixture in the exhaust pipe, triggering o2 sensor fault reading!