Need to install O2 sensors, in aftermarket exhaust with no clue where or how

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I have a 91 I purchased with a blown head gasket. I am putting that back together and looking over how to desmog it only to discover I have no O2 sensors. From the reading I have the done the 3FE will run without them, but not as well.

The PO had the exhaust cut off not far behind the manifolds, Y'd into a single that goes over the crossmember and into a muffler that turns down in front of the axle. I have found 1 of the plugs for the sensor but not the other.

I have done some searching but can not find the info I am looking for.

What would be the best way to install O2 sensors with my exhaust being mostly aftermarket pipe? From the looks of the denso sensors I need a whole for the probe and then a way to bolt the flange down. It looks like a flat surface would be best, not round pipe. I though about drilling and tapping the exhaust manifolds but then would have to lengthen the harness for the sensors, and not sure if they can handle the extra heat that close to the combustion process. Doable for sure but dont know if this is the best way.

Any help is appreciated.
 
You need the mounting flange. You should be able to get them from amazon. Then you need to drill a hole so the sensor can portrude into the exhaust pipe and weld the flange on in that spot.

o2_Crop__94315.1496185226.jpg
 
Awesome, thank you. I will see what i can find on amazon
 
One goes up stream of the CAT and the other needs to go down stream. I put mine about 30-36 inches from the exit point of the CAT. There might be some pics of the locations in my build thread. Mines a 1997 but guessing sensor plug locations are similar.

I ordered the flanges from SLEE offroad. They are stainless which I could not find on Amazon.
 
One goes up stream of the CAT and the other needs to go down stream. I put mine about 30-36 inches from the exit point of the CAT. There might be some pics of the locations in my build thread. Mines a 1997 but guessing sensor plug locations are similar.

I ordered the flanges from SLEE offroad. They are stainless which I could not find on Amazon.

That is true for the 95-97 ODB2 models but both the 91-92 with the 3FE motor and the 93-94 with the 1FZ-FE motor which are both ODB1 versions use two side by side cats that have an O2 sensor in front of each cat.
 

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