hello im new to this forum and not sure if this was covered. but my father bought a 2000 f150 5.4 about a month ago and the previous owner had it staright piped because the cats were plugged. well as most people know this isnt a good idea for these trucks and whoever staright piped it removed the o2 sensors as well. no holes to put them in ethier well i just bought two magnaflow cats and i want to weld them on. but i also want to replace the o2 sensor and i have no idea where they would plug into? i well have the exhuast shop weld in the holes for the sensors just need to know where they go not sure why someone would remove them in the first place the truck runs horrible

 

In their stock locations, the front sensors are located in the head pipes about 5 inches from the header flanges.
The rear sensors are located in the 'middle' of the rear cats.
You should have codes for the missing cats as several codes groups would be present under normal conditions.
.
Without sensors the motor is running 'rich', on fixed fuel tables in the computer program.
The codes for missing and non output signals would normally present.
They are for non switching on both sides and open heater circuits.
Also the codes for failed cat performance normally monitored by the rear cats should be set as 420 and 421 or may be Zeroed if looked at with a Scanner because the signals are not useful after a determined amount of time..
Once cats are installed and sensors connected, all codes should clear unless there is still something out of order.
The sensor harnesses come out of the main harness coming down the passenger side rear of the motor and feed the transmission shift control, and fuel tank monitors along with the front and rear Ox sensors.
Each sensor has 4 leads. Two for the heater and two for signaling the computer to adjust fuel injection full time.
Note that one fuse powers all these circuit. If it were to blow due to a short to ground it affects a lot of systems and generates a lot of codes plus the trans shifting would be greatly affected.
.
Just bypassing like this shows a lack of knowledge about what cannot be done legally to the operating system without consequences of some sort.
A question is, are you sure the front sensors in the head pipes are missing? They normally would not be removes on a Cat bypass mod unless the whole pipe was replaced. If they are still in place, you may have another issue such as an air leak.
The only way to tell about the final result is to look at live data with a good Scanner after all the mechanical issues are addressed.
Good luck..

 

oh thank you i havent checked the front yet but i know the rear are missing