Oops... when removing the oxygen sensor it appears the exhaust manifold "ate" the threads of the O2 sensor. The treads in the manifold look like they might.. or might not... be ok. At the very least it seems prudent to tap the threads with the correct size and see if the new sensor will seat correctly.
How can I find out the correct size to tap the threads?
Are there other options?
an insert?
Or JB weld and then replace the manifold when the sensor goes out again in 10 years.
It was throwing a P0135 code and the mileage was horrible so I am hoping I didn't actually create problems for myself.

 

O2s use 18mm x 1.5 threads

Most hardware stores and autoparts stores would have the tap size on hand

No other options really
There are clamp on O2 bungs for exhaust pipes, but you would still need to plug the old O2 sensor hole so would need at least some good threads for the plug to grip and hold

 

Thank you so much Ron! Much appreciated.

 

Welllll… I found an O2 sensor tap fairly easily but the threads in the exhaust manifold are galled quite severely.

When removing the O2 sensor from the manifold, metal from the old sensor was deposited on the manifold threads so drastically and of an amount so great as to prevent the tap from being able to enter and engage the threads to remove the deposited metal.

I am considering heating the manifold with a small propane torch in order to soften the deposits enough to facilitate removal.

I am open to any and all suggestions.

 

Still stuck with damaged manifold threads. Heating with propane Turbotorch for 30-45 secs and then picking at the threads and working the 18mm thread chaser is removing some fine shavings but no real momentum on getting it back to useable. I wonder if it can be drilled out and a helicoil installed? And if so what are the chances of drilling it straight enough to install a helical successfully with the manifold in the vehicle. Any thoughts are appreciated:)

 

You will need to pull the exhaust manifold

The little bit of remaining thread using a tap shouldn't hurt the Cat Converter
Drilling would be too much metal inside exhaust, so not recommended

You should use a 1998-2001 2.5l replacement manifold, Ranger or Mazda are the same

Check car-part.com

They run $30-$80 from wrecker, or should, I show at least 5 2.5l exhaust manifolds within 30 miles of my location

 

With visions of dealing with the difficult removal of at least 10 baked in exhaust manifold nuts and possibly bolts etc. it seemed a better option to try a full size Tap as a last ditch attempt to reform the damaged O2 Sensor threads.

It worked nicely using the proper tap. The short tap on the left is a Lisle branded part which was not able to get a purchase on the galled threads. It cost $8. The tap on the right with the longer more gradual taper was able to work its way down in to the hole to clear the galling and restore the original threads.

$18 from Amazon. It was slow going with 1/4 and 1/2 turns forward and then backing it completely out to clear the shavings and add more cutting oil. The final result was a useable threaded hole.
https://smile.amazon.com/dp/B000GTJC...roduct_details

Well I hope this may be helpful to someone. Possibly keeping them from attempting a complete exhaust manifold replacement. Of course the CEL is still there even after installing the new O2 sensor, DPFE(Exhaust Gas Recirculation Pressure Feedback Sensor), and an EGR time delay switch.

Next up is to trace the tiny hoses attached to the EGR switch to check for breaks and loose connections.