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I was about to replace a '93 945's (Regina) Catalytic Converter and O2 sensor. I ordered the parts (Bosal 099-942 & Ntk 25002). I receive the parts. I remove the old components. Upon closer inspection of the new catalytic converter, I notice that the catalytic converter O2 sensor bung is too long for the Regina O2 sensor type. The old O2 sensor and the new one are the same size, length, and type. The new catalytic converter's bung is almost twice as long as the old catalytic converter's bung is. I need some help, some advice, and a few questions answered.
(1a:) Should I just take the catalytic converter to an auto machinist shop and have them trim the bung? (1b:) Is this possible?
2: Is the length of the bung not really an issue?
3: What is the best course of action for this unexpected issue?
Any insight, answers, or help provided is appreciated. Thank you.
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Four years ago my 1995 945 NA failed NOX by a huge amount. My local indy checked it out and told me I needed a new catalytic converter and air mass meter and quoted me a pile of money to do it. Turned out all it really was, was a dirty electrical plug connector to the air mass meter. Cleaned it up, and it has been passing smog ever since.
John
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Dear hanacaptain,
Hope you're well. Great insight!!! If the air mass meter malfunctions, that could explain "rich" condition and so carbon deposits in the cat.
Thanks for sharing!!
Yours faithfully,
Spook
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The only cach is this is a Regina - no AMM. I'm just wondering if something like a bad coolant temp sensor is out of whack and creating an over-rich condition which is sooting up the cat. Could it be that the O2 and cat are actually OK and the over-rich fault code is genuine? Regina O2 sensors are known to practically be a lifetime part. And the cat honeycomb is still solid???
--
Current rides: 2005 Volvo S80 2.5T, 2003 Volvo V70 2.4NA, 1973 Volvo 1800ES (fixed the ignition - now back to the brakes again)
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Dear Chris Mullet,
Hope you're well. Good catch as to no air mass meter on a Rex-Regina engine!!!!
You may well be correct as to the coolant temp sensor having failed. I wonder if there's a way to "de-carbon" a cat converter. I can't recall that subject having been discussed.
Hope this helps.
Yours faithfully,
Spook
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"...I wonder if there's a way to "de-carbon" a cat converter...."
There are videos on Youtube where the guy flushes out a dirty cat with soap and water - probably a strong detergent. Maybe it works - I'd say try at your own risk. But if you're about to throw the cat away, what's to lose? I just hate to see an OE Volvo cat go into the trash needlessly. They're so superior to the aftermarket units. (and so expensive)
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Dear Chris Mullet,
Hope you're well. The core of the converter is a ceramic "honeycomb", to which is bonded (or in which is embedded) precious-metal-based compounds. Heat enables those compounds to convert exhaust gases into more bening compoounds.
A failed cat converter should not be "thrown away". The precious metal content is considerable. Thus, a failed unit should be recycled. Salvage yards will pay for a failed converter, and then sell it to a re-cycler.
If soap and water remove the carbon - which I doubt - I'd put the converter in an oven (low heat, e.g., 250 degrees) for a day or so, to "cook-out" the water.
Hope this helps.
Yours faithfully,
Spook
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I need to be more careful with my terminology. I know they're worth enough for people to steal them off of cars for their recycle value. And the hoarder/cheapskate in me says don't get rid of the Volvo cat quite yet.
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Dear Solo_,
Hope you're well. It's been some time since I looked at the cat converter on my '93 940 Rex Regina. As best I recall, the opening for the oxygen (O2) sensor is through a "plate" welded to the surface of the cat converter's shell. The plate has an internally-threaded hole.
Does the new Oxygen sensor thread smoothly into the new cat converter's opening? I
Further, when you use the term "long" to describe the "bung" (or opening) in the cat converter, do you refer to a metal tube (internally threaded) that is welded to the cat converter's shell? Or is the "bung" a thick steel plate (with an internally threaded hole), welded to the cat converter's shell?
How long is the tube - or how thick is the plate - into which the O2 sensor is to be mounted?
What are thee dimensions on the old cat converter?
I'd guess that a 1/4" long tube - or 1/4" thick plate - would provide enough threads to hold securely an O2 sensor.
Hope this helps.
Yours faithfully,
Spook
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Hello again Spook,
Do you happen to know what that bung near the end of the downpipe is used for? Could it be an alternate location for placement of an O2 sensor?
Thank you again.
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Yes, some model years mount the O2 sensor in the pipe - with corresponding shorter wiring. There should be a plug in the bung. -- Dave
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Hi,
The sensor end of the 02 sensor should fully protrude into the space where it is exposed to the moving exhaust gasses to measure the 02 volume (mass?) by heat of the total exhaust volume. The sensor tip should not be in any way recessed into the internal threaded channel of the bung welded to the exterior.
"The new catalytic converter's bung is a round tube that's internally threaded that is approximately 5/8" long. The Rex Regina's O2 sensor is only 13/16" long (measurement taken from the base below the crush washer) and its threads are only a 1/4" long (measurement taken from above the crush washer). This only leaves about 3/16" or less of the sensor's tip to actually clear the bung."
The 02 sensor bung welded to the catalytic converter is too deep (thick), or too long, for the 02 sensor tip to fully protrude into the exhaust chamber upstream of the exhaust catalyst. You see vents at the tip. The sensor thread should be flush, or protrude slightly, as you see it installed. (Imagine if you will a rear-wheel drive Volvo ....)
The Bosch 02 sensor on a normally aspired Bosch engine control equipped 240/740/940 has the same thread reach, iirc. I've futzed with Bendix Regina / Rex, yet not often nor recently.
It may be best to contact the retail vendor from whence you made purchase, explain the issue, and make for exchange or return.
If you are confident an auto exhaust repair service can exchange the oxygen sensor bung on your replacement catalytic converter, you will void the warranty. I'll guess the available replacement catalytic converter for our vintage and equipped model Nordica autos would not fail so long as the engine is in good condition and tune with good operating economy and proper emissions. With proper tune, these cars can burn very cleanly.
I indicate as such as, even though my 1979 242 GT stock had a catalytic converter in 1992 or so after four years of ownership, the catalytic converter failed. A Milwaukee, Oregon auto exhaust repair service had a brand they installed in 1989-1991. The exhaust gasses were proper, as measured at the exhaust bung in the header pipe. (A hex bolt was in the headr pipe bung. Maybe whut you see?) The 02 sensor then worked yet weak. Replaced 02 sensor at the same time. Ran way better and more sprightly. Mileage went up. It was not Bosal or Starla. Stupid me. The replacement catalytic converter failed in 1992-3. So I guess I got a brand name replacement.
There may be other solutions. Hope that helps.
When you solve the issue, use high temperature nickel anti-seize on the thread before install and torque. (I used lead anti-seize once on mine! He-he.)
Drove it to the yunkyard with clean emissions 15 or so year ago. Rust. Gave the battery away.
I'll guess you read the FAQ for other info?
Sorry to prattle on so.
Happy Friday,
MacDuff.
--
Give your brickboard.com a big thumbs up! Way up! - Roger Ebert. 
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Hello, Spook.
The old catalytic converter's bung is a round tube that's internally threaded that is approximately 1/4" long. The new catalytic converter's bung is a round tube that's internally threaded that is approximately 5/8" long. The Rex Regina's O2 sensor is only 13/16" long (measurement taken from the base below the crush washer) and its threads are only a 1/4" long (measurement taken from above the crush washer). This only leaves about 3/16" or less of the sensor's tip to actually clear the bung.
The O2 sensor threads smoothly into the new catalytic converter's bung. There are no issues with the fitting of the O2 sensor into the new catalytic converter.
The old catalytic converter and the new catalytic converter are roughly the same size. The new one may be about a 3/4" smaller in length (measurement taken from catalytic converter body where the Insulation Packaging at the front would begin, to the end of the Insulation Packaging at the rear) and 1/2" smaller on diameter (measurement made of catalytic converter body) than the old one.
I just don't think that 3/16" of the sensor's tip exposed to exhaust gasses would be sufficient for proper O2 sensor operation.
(Addendum): Upon further inspection of the old catalytic converter, the substrate materiel is black, but not broken up or melted, and there are no clogs in it. It does not rattle when shaken. Not sure if this is my issue with the car. The only reason that I am changing it and the O2 sensor is because of the High NOx issue with this car. I have already checked for vacuum leaks and exhaust leaks (before the catalytic converter). There are no leaks either way. I was told that if there was a vacuum leak large enough to cause the NOx levels to be almost three times above the limit that I would be able to hear the leak. But I checked for leaks anyway. While checking for leaks I changed the oil, cleaned the flame trap, throttle body, and idle control motor (it was filthy). Doing this smoothed out the car's idle (it was surging between 500rpm to 700rpm).
Thanks for the response. I hope that your day is going well.
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Dear Solo_,
Hope you're well. If I correctly read your nicely detailed reply, the O2 sensor is supposed to be screwed into a 5/8"-long tube, that protrudes from the cat converter's shell. If this reading is correct, then the tube should be shortened, so that it is 1/4" long. The O2 sensor's tip will then be positioned inside the new cat converter just as it was in the replaced cat converter.
I'd use a thin abrasive cutting wheel - 1/16" thick - to shorten the tube by 3/8". That will leave about 1/4" of threaded tube, which should be enough to secure the sensor.
Aftermarket parts-makers sometimes change part specifications for no obvious reason. An example: there are made-in-China harmonic balancers (crank pulleys) that have slots inside the pulley's hub, too narrow to accept the Volvo crank pulley counter-hold tool. Why the maker of these after-market pulleys made the slots too narrow - they are about 6mm wide, rather than the 7mm needed to allow the Volvo tool to fit - is a mystery. Perhaps the maker was unaware that there's a special tool that eases removal of the crankshaft pulley's center bolt.
The cat maker may have thought that a 1/4" tube was not enough to secure the O2 sensor. The "improvement" - the 5/8"-long tube - needs to be undone, so that the sensor's tip will be propertly positioned in the exhaust stream.
The black coating on the honeycomb inside the cat converter is a sign of an over-rich mixture. The black is carbon, the residue of unburned fuel in the exhaust, that burned when it contacted the super-hot cat converter. The carbon coating likely kept the cat converter from working properly. I'd check the sparkplugs. If the tips are carboned-up, I'd try to find out why too much fuel - or too little air - is being supplied.
Hope this helps.
Yours faithfully,
Spook
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