Rear O2 Sensor Broke Off in Header

Big McLargeHuge · 16 March 2020

Hi all,

In the middle of replacing both my front and rear O2 sensors, car is a 1990 NA1 so just two sensors on the headers.

The front sensor came out just fine with a box end wrench and some heat (no penetrating oil since I read leftover oil can mess up the new sensor).

The rear sensor not so much, I used a socket-type O2 removal tool, cut off the wiring to get more space, heated up the bung, and went to town on the sensor. Results below.

The threads on the sensor completely sheared off, leaving most of the remaining ~4 threads and the ceramics & sensor head inside the rear header.

I've been going at it with penetrating oil, propane torch, reverse bits/screw extractors, but it hasn't budged yet. I would really prefer not to have to remove the header itself since it will likely create the same problem since the heat shield bolts were already stripped and rusted out, and likely the header bolts are very rusted as well.

Any ideas for removing this in situ? If I had to run the car as-is to get to a shop or somewhere, would the exhaust leak through this bung? Obviously would have a CEL for the rear heater circuit regardless.

If nothing works, I wouldn't mind taking it to a mechanic and having them work their magic, but I haven't found a good one in my area yet and don't know how much they'd charge. This is the DIY forum after all.

Thanks in advance.

Old Guy · 16 March 2020

This is a wild assed suggestion because I have never been in your situation. I have never examined the OEM narrow bands; but, on wide bands the center core of the sensor where the ceramic insulation is located is largish. If you can get a punch and hammer into the area (a fairly large if) you should be able to smash out the core of the sensor (the debris will end up in the manifold). With a large hole in the sensor you have two options:

- this requires quite a large hole. With a radial hacksaw blade (looks like a tiny key hole saw) fit the saw into the hole and try to make a radial cut in the sensor body. The radial cut will relieve pressure on the body which may allow subsequent extraction.
- skip the saw and fit the largest screw extractor possible into the core of the sensor and hope for the best.

For either option I would apply PB Blaster (not WD 40) and let it soak. You can clean up the residual with brake cleaner - assuming you are successful. The debris from the sensor will end up in the manifold so you should disconnect the cat and fish a small vacuum hose up the manifold to extract the debris. You don't need this stuff embedding itself in the cat core creating new problems.

Personally I give my suggestion a low probability of success, particularly because of the location of the sensors. I suspect that manifold removal is in the cards; but, defer to anybody who has actually dealt successfully with this problem.

O2 sensors require a reference to atmospheric air. As long as the sensor element itself and the supporting structure around the sensor is not damaged there is no direct channel from the exhaust side to the reference air side of the sensor so hypothetically no exhaust leakage. However, you have twisted the top off so there is a risk of collateral damage to the sensor element and a leak. So you might have no exhaust leak or a small exhaust leak which will likely not present a risk. Of course, if you followed my suggestion and smacked a larger hole into the sensor that is slightly different. But, it will still be a smallish hole. It will be noisy; but, the exhaust leakage will likely not present a health risk in the context of a reasonably direct drive to a mechanic. In this case, do check for anything combustible in the area - you don't need hot exhaust gasses leaking form the hole melting something or starting a fire.

Good luck with it!

nigel · 16 March 2020

threads

Aero-Kroil and gold anti-seize in the new O2 sensor.

Cheers

nigel

Big McLargeHuge · 16 March 2020

Old Guy said:
This is a wild assed suggestion because I have never been in your situation. I have never examined the OEM narrow bands; but, on wide bands the center core of the sensor where the ceramic insulation is located is largish. If you can get a punch and hammer into the area (a fairly large if) you should be able to smash out the core of the sensor (the debris will end up in the manifold). With a large hole in the sensor you have two options:

- this requires quite a large hole. With a radial hacksaw blade (looks like a tiny key hole saw) fit the saw into the hole and try to make a radial cut in the sensor body. The radial cut will relieve pressure on the body which may allow subsequent extraction.
- skip the saw and fit the largest screw extractor possible into the core of the sensor and hope for the best.

For either option I would apply PB Blaster (not WD 40) and let it soak. You can clean up the residual with brake cleaner - assuming you are successful. The debris from the sensor will end up in the manifold so you should disconnect the cat and fish a small vacuum hose up the manifold to extract the debris. You don't need this stuff embedding itself in the cat core creating new problems.

Personally I give my suggestion a low probability of success, particularly because of the location of the sensors. I suspect that manifold removal is in the cards; but, defer to anybody who has actually dealt successfully with this problem.

O2 sensors require a reference to atmospheric air. As long as the sensor element itself and the supporting structure around the sensor is not damaged there is no direct channel from the exhaust side to the reference air side of the sensor so hypothetically no exhaust leakage. However, you have twisted the top off so there is a risk of collateral damage to the sensor element and a leak. So you might have no exhaust leak or a small exhaust leak which will likely not present a risk. Of course, if you followed my suggestion and smacked a larger hole into the sensor that is slightly different. But, it will still be a smallish hole. It will be noisy; but, the exhaust leakage will likely not present a health risk in the context of a reasonably direct drive to a mechanic. In this case, do check for anything combustible in the area - you don't need hot exhaust gasses leaking form the hole melting something or starting a fire.

Good luck with it!

Thanks much for the input. I agree it would be possible to smash the sensor core into the exhaust, though not much room for swinging a hammer. Trying to avoid doing this since, as you said, they will find their way onto the front of the cat honeycomb. To be honest, mostly concerned about causing rattling in the exhaust and not so much about the cats since I will be replacing them soon enough.

Also not looking forward to removing the cat since the studs/nuts and heat shield on it looks so bad that I'm sure I would create new problems. I was hoping to save them for when I put in full headers/test pipes/exhaust to avoid the whole issue, the studs are nearly unrecognizable.

I do like the idea of cutting into the sensor body, though I'll have to find the right size saw and hack at it for quite a while. I have screw extractors I've been jamming in and really wrenching on, but I hit a point where the extractor is so tight that the only wrench that will fit is an adjustable one and the ends start to give way with that much torque. I need some sort of square drive ratchet/socket combo for that.

I left the extractor in the sensor hole for now since it is seriously wedged in there and won't come out without me removing it, in the hopes that it might reduce exhaust leakage in the short term (lol). I'm sure if a mechanic was willing to fix this for me they would be very confused at the extractor sticking out of the header.

I looked and there doesn't seem to be anything meltable or flammable in the path of the sensor, though it will probably soot up my rear engine bay. I won't be driving it for longer than it takes to get it to a shop anyways, but I'll give it another afternoon before I phone it in.

nigel said:
Aero-Kroil and gold anti-seize in the new O2 sensor.

Cheers

nigel

The new sensors come with anti-seize for the threads (which I applied to the front sensor, already replaced), and I've been shooting this bung with liquid wrench and a propane torch for 3 or 4 cycles. Next idea is a MAP gas or hotter torch to really get it cherry red.

nigel · 16 March 2020

Again

Again, Aero-Kroil and let it soak for 15 min or so. We use to release stubborn turbine disc bolts and it works. Free All works as well.

Cheers
nigel

nigel · 16 March 2020

Also

NO smacking the old threaded end of the old sensor out! You’ll just cause more damage to the manifold.

Cheers
nigel

Ponyboy · 16 March 2020

AeroKroil works exceedingly well. I don't even bother with WD-40 or PB Blaster anymore. But even so, you may have to drill the remaining half of the sensor out.

Big McLargeHuge · 17 March 2020

nigel said:
Again, Aero-Kroil and let it soak for 15 min or so. We use to release stubborn turbine disc bolts and it works. Free All works as well.

Cheers
nigel

Ponyboy said:
AeroKroil works exceedingly well. I don't even bother with WD-40 or PB Blaster anymore. But even so, you may have to drill the remaining half of the sensor out.

Mmm, good to know, I'll pick up a can. Didn't know there was a super duty oil to use.

Well, can't promise I didn't smack the inner sensor threads a teeny bit, but it really is not making a dent except on the stuck threads. Hopefully with AeroKroil I'll have more luck with my extractor bit, I can get a lot of left-handed leverage on the sensor but no movement at all, almost twisted my extractor. Hopefully the AK loosens it up.

For now, I drove the car with my extractor gutentight in the sensor threads and didn't notice any extra noise or leaks, so I should be able to get it to a shop worst case. Kinda like a redneck NPT plug.

Kaz-kzukNA1 · 17 March 2020

With the limited space, the shop may end up removing the rear exh manifold from the engine.

You may want comparing the price for extracting the broken sensor VS replacing the manifold with the healthy used one.
There are so many owners with the aftermarket headers so chances are, someone should have that heavy anchor OEM rear exh manifold somewhere in their storage.

Could be cheaper and quicker than trying to extract the broken sensor and possibly repair the damaged boss.

Or, just go with the aftermarket header all together.

50/50 mixture of acetone and ATF works great but be careful handling the fluid.
It can dissolve so many things….
Be careful with acetone especially if handling burnt Viton (used as adhesive for loom, heatshrink tube, etc) or any chemicals.
The dissolved chemical can penetrate through your skin surface and cause health issue in the future.

Kaz

Old Guy · 17 March 2020

Well Kaz provides an excellent thought. Provides the ultimate rationalization for upgrading to the later na2 headers or some aftermarket tubular headers :smile:.

A side note on acetone. From a health perspective, acetone is one of the less nasty chemicals. Probably less nasty than any of those carb / sensor cleaners. As I recall from its MSDS it is not listed as a carcinogen. The two primary health issues are breathing in the vapours (applies to just about all organic chemical solvents) and dermatitis. If you breath in really high concentrations of the vapours extreme respiratory distress can result. That should not be a problem unless you are washing large areas. Acetone is an excellent degreaser and it will remove all oils from your skin leading to an interesting case of severely chapped skin. Gloves are in order.

Big McLargeHuge · 17 March 2020

I agree this would be a good excuse to go aftermarket headers, which is definitely on my short list, but I haven't converted the car to M/T yet and it seems like a lot of the options say M/T only, I assume because of clearance issues?

I think moving forwards I'll try the Aero-Kroil and extractor first, hopefully that will be the silver bullet I need to break the thing free. Supposed to be arriving from Amazon on Sunday, I think the current global situation has severely inflated delivery times

.

Not particularly concerned about acetone itself, but I'll have to figure out an application method since acetone eats plastic easily. Maybe a brush? I do have some Toyota WS lying around

Otherwise, I'll have to take the rear header off, and as you suggest, it would likely be easier to use someone's leftover header instead of attempting to extract mine.

Big McLargeHuge · 2 July 2020

Here's an update for anyone that cares, I tried for about 2-3 hours a while back with Kroil and various extractor bits, but nothing helped at all and the most I could do was basically shave off the O2 threads from the inside since they were too soft to allow the outside rust to break loose, so removing the header is the only option. There's not enough room to try anything else.

I tried to get a used cheap OEM boat anchor header to swap over, but had no luck getting one for a few weeks. The Pride V2 headers I wanted came back in stock (one of the few that fit A/T's) so I just got those and will be doing a full exhaust job soon. In the meantime I've been running with the bung plugged and no rear O2, so I have a permanent CEL for the missing sensor but it allows me to drive around, just with poor gas mileage :biggrin:. Thanks all for the suggestions.

Rear O2 Sensor Broke Off in Header

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