Hiya Uncle OldDuke!

Happy Friday to you goodly Sir in young tonnes!

Hope all's aces and eights for you and yours and your Volvos today!

I'd read your thread about jack. I have a made in China sears jack. Leaks like a sieve until about halfway. No rebuild kits for these. So, I try to collect what leaks back out. Some of that Ford Type F, or the heavier, thicker Type G works. Maybe a good 70W? I dunno. Maybe pull the thing apart and try to measure up replacement O rings that are square or round in edge on profile?

Oooph, I dunno if I'm so good at responding to a question sometimes. The vagaries of bad and good moods of life: unrequited (or stolen). (A title to a narrative I wrote many years ago as a straight drama. The anti-protagonist protagonist, as with all stories I used to write, drives a RWD Volvo. All the good good guys drive Volvo automobiles when I write them. The scenes of the protagonists serving their Volvo, sometimes mechanical, sometimes wet, like oil change, I use as metaphor [rhetoric as actionables as the scene and actor agency] placed beneath the dialogue the characters trade during the scene.)

Though I feel better today as I'm about to go back to St. Louis for some good pizza and dating a woman.

Sorry to be so late replying. It takes me sometimes a few hours to reply to one post when you see a verbose reply. So, I don't get to read all the posts. I get tired. I try to create the whole shabile to put in the mind of the original or subsequent article or thread poster. Such is my folly. I should reply like you, Professor Art B. PhD. & DSc., Dan, Onkel, and folks. I see Professor Porter replies here too. Just a few response lines to get the dialogue going.

I'd imagine anyone else here better to answer on the 02 sensor trick, or restoration of an 02 sensor that is week on the 02 volts output.

As aforementioned here, the 02 sensor can either be at fault, or you have a clogged cat. The balance between the AMM/MAF as air mass intake measured to the 02 that remains in the exhaust gases once they reach the 02 sensor through all leak-free exhaust plumbing to that point.

So, you know how to check the voltage the 02 sensor generates as it warms.

Yet a clogged or partially clogged catalytic converter can disturb the AMM/MAF with the 02 sensor balance. Exhaust gases shall flow freely.

You may have a strong 02 sensor, and on warm up, your multimeter set to low DC volts may show the proper range at idle, where less exhaust gas mass exist the engine exhaust ports, so partial restriction at the (partially) clogged catalytic converter may show well.

Are you certain you have no exhaust leaks at any union up to and including the header pipe out put and the catalytic converter input. A weak solution of detergent water, like lemon dish detergent can yield clues with bubbles. Even small pinhole bubble in the header steel pipe material.

Though an exhaust leak may mean a lean or rich running condition in the socket #2 OBD-1 fault codes. Check the socket #6 also. Repeat until no new codes display.

You can remove the header pipe and the catalytic converter. Have extra gaskets, hangars, and exhaust clamps on hand. Soak with the PB Blaster or perhaps use heat as you are in the Hatlantic Northeast rusty belt, yes.

The hardware that secures the header pipe output and the catalytic converter input is frail. If the flange (you should have the triangular spin flange, yes?) plate carbon steel is good at both ends, the catalytic converter shell in good shape, you may be able to restore it.

If you have the anchored studs on the catalytic converter input flange, and these are rusted, and these break, with a press or drill, you can press these out. These studs press into the flange on splines like wheel lug stud hardware on our 240 hubs.

I'd not done this myself. I saw someone do this on some eighties Ford Mustang with the four cylinder as he was not passing CA-state emission (smog) inspection). This event was in like 1991 in Chico, CA.

After freeing the catalytic converter:
- Tip it forward and tap the shell with a piece of wood. Black carbon dust may collect. It is hazardous. Do not breathe it at all. Repeat and tip it backward.
- Place a strong light in a darkened room at one end. Do you see any light through the catalytic converter?
- In sunlight, or with strong spotlight like light, peer into the input end. How's the honey comb ceramic substrate?

The substrate heats from center outwards concentrically towards the inner housing shell. So, usually, collected, condensate hydrocarbons collect outward in or from the bottom up. I'd seen this in engines with poor oil control at the piston rings or on Hondas with failing valve guides and oil control piston rings. Usually coincides with stop and start driving. I'd also seen this on the big American V-8 engines through the 1990s of all makes where the owner / operator performs grocery getting and never lets the exhaust, including the clogged catalytic converter, get hot enough and dry out. You'll see municipal fleet cars in large cities at a stop light. And then they'll go at the green light, spewing fluid right out the tail pipe! That's just the beginning of exhaust and catalytic converter failure, including clogging, if the fuel to air ratio is rich.

The other way is as we know when the fuel to air ratio is far too lean, causing a hot combustion that can actually damage the ceramic substrate if not displace the platinum-palladium-rhodium reactants or reagents living and infused in the ceramic substrate. The melted ceramic substrate can also cause a clog, though this events usually results in a rattling catalytic converter or a cat ball that clogs the exhaust flow when accelerating or you are driving with exhaust gases pushing against the cat ball that is clogging the outlet end business of the clogged catalytic converter. (I always misspell catalytic converter.)

- If the substrate appears fine and securely bonded inside the catalytic converter, yet you do have a partial clog, you may be able to use myriad solvents to weaken the hydrocarbon condensate. What solvents you may use, I dunno. You can damage what good portion of functioning, unclogged substrate remains. Yet you want a durable solvent that actually weakens a clog cause by hydrocarbon condensate. Brake parts cleaner is reside and silicon free (no silicon anything near the catalytic converter or certainly in it).

Some hydrocarbon condensate in the catalytic converter can be some very durable forms of carbon and hydrocarbon that won't break down in spite of a solvent. Some of this stuff, I was told one by the one and only and great Howard Erlanger, and his Sports Car Centre in Fenton, MO (Ferrari AND Volvo and other Service!) can be as touch and chemically similar to the stuff that turns into diamond. Like the carbon build up on intake and exhaust valves.

I'm thinkin' of solvents for you. Though the price per bottle may be pricey.

As for the 02 sensor, that's easier if you have hydrocarbon condensate build up that does not burn off due to a clogged catalytic converter. Brake parts cleaner and a steel bristle brush, or maybe brass, that is a clean brush to start with. You may want to soak the 02 sensor tip, er, immerse it, in something like the Chevron Techron or Techroline(?). Let sit for some time. Cover to prevent solvent evaporation. Try to avoid the part above the 02 sensor securing thread and certainly the 02 sensor cable. You can let soak, and the solvent may darken like steeping your fave earl grey tea over time. Some carbon build up may be outside the vented steal envelope at the 02 sensor end, clogging the vents. Some may be built up inside and the 02 sensor heater element may be overwhelmed to burn off the carbon guck. Though if the heater does not work, you may get fault code 2-1-2 at the OBD-socket 2. Art B., I think, makes mention of the driver, or output stage on the EZK ignition model, that may not be encountering the 02 sensor heater load. Wiring? Corrosion at the connector? Or it could be a fault with the IC amplifier output on the EZK module control board. I may be confusing this with the AMM/MAF wire burn off function on engine shut off failing on the LH-Jet ECU. It may have been Art B. I dunno.

I'm not good with the solvent naming today. Something that does leave residue, or residue that is not offensive to the 02 sensor tip.

Seafoam? For the catalytic converter interior? To melt the guck in the catalytic converter ceramic substrate, with damaging the catalytic converter itself? Spray some in and place the outlet end down to drip out? Or, let set flat and the Seafoam stuff spends some time making friends with the hydrocarbon condensate in the catalytic converter. Roll it from flat side to flat side.

IIRC, the SeaFoam stuff is used or sprayed into the air intake to remove the hydrocarbon condensate from the air intake and through the combustion chamber and out as the engine runs. I'd not used the procedure myself of seen it done before. Yet even in the liquid state, it should not pose a problem to the catalytic converter innards, I guess. I'm not sure. The process may take several applications over days. Each application may take several days. Stuff the inlet and outlet ends so the SeaFoam does not evaporate quickly. The process is massively dangerous and flammable. SeaFoam is highly toxic.

Don't use turpentine or other like spirit, though that could work also. The pine sap residue in the spirit may not work well. Maybe a mineral spirit, yet the heavier oily hydrocarbons.

You'd tip out the SeaFoam at the front and rear. You could then use a bottle of brake parts cleaner (I dunno whether the chlorinated or non-chlorinated, chemistry not my thing here, yet non-chlorinated seems somehow better.)

May may need only one can of SeaFoam and maybe one or two cans of brake parts cleaner. There may be other solvents to 'rinse' out the hydrocarbon condensate in the catalytic converter that is dissolved by the SeaFoam. Don't use gasoline or any such fuel like diesel or kerosene.

It may take several generous SeaFoam applications at several days each to melt the hydrocarbon condensate in the catalytic converter. What comes out may be nasty, yet grimey.

Let dry over time. You do not want a fire in the catalytic converter. Though doing this job, versus replacement, comes with risk.

You may not need to get out all of the hydrocarbon condensate in the catalytic converter. Enough to open up a path for exhaust gases to do their job as they pass through and heat the ceramic substrate.

If you know all engine control systems work, reassemble all.

May want to disconnect the battery or pull the fuse to clear any codes and then allow the ECUs to remap.

Start the engine and test the 02 sensor on warm up. Does it react as it should with your mulitmeter? If yes, there's one success.

You'll get nasty smoke coming from the tail pipe as stuff begins to burn out of the catalytic converter. Maybe start with the idle and then bring up the engine RPMs to like 1500 or so RPM. No need to go faster. As the engine is not pulling the Volvo 240 weight, it means a lean burn through and out of the engine. The heating catalytic converter may then burn off the hydrocarbon condensate that remains. Your neighbors may protest. I'd not drive it with a bunch of smoke coming out of the tail pipe. Take a look under the car at the catalytic converter. You do not want it to get so hot as to display red.

I dunno the normal exterior catalytic converter temp. An IR thermometer can help as you bounce the red dot on the catalytic converter exterior. Whatever the normal value, it may get a little warmer. If the temp value at any point rises very fast, you may have a cat fire.

Keep a fire extinguisher nearby or several.

As the smoke clears up, and the engine seems fine at idle and at 1200-2000 RPM, maybe then take for a test drive when the smoke clears.

Every so often check the catalytic converter temp.

The best action to a clean catalytic converter is proper emission controls with proper fuel to air ratio on drives long enough where the engine oil boils out all the combustion by-products through the PCV (so you have dry engine oil, if not new engine oil) and then the exhaust system heats up from stem to stern as normal.

Just hope such an effort works to save your catalytic converter.

I employed some imagination here where memory fails.

Hope that helps.

Questions.

Thank you,

MacDuffed to St. Louie.
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Volvo 164: The Mightiest, most Powerful, most Beautiful Volvo Automobile Forever