Recently, a mechanic that installed headers on a friends 3.0 told him that the O2 sensor was not necessary on his truck (1990) and didn't weld on a flange for the sensor. This seems incorrect to me but the mechanic has years of experience. What will happen if it is run without a oxygen sensor? Thanks for any information.

 

Definitely not the authority on the matter, but as I understand it, without a direct O2 reading, the computer will default into open loop mode, running the engine on preset values as opposed to taking real time readings from a non-existent sensor. I'm pretty sure those preset defaults are nowhere near as efficient as real time information though, so maybe slight performance and mpg suffering.

 

Definitely need the O2 sensor on an EFI for it to run properly

 

That mechanic is an idiot, you definatly need an 02 sensor for the fuel injection to operate properly. I would tell your friend not to go back to him again for any other engine work.

 

his credibility is shot.. no efi car/ truck opperates without an o2 sensor.