Odd repair shop situation

In reply to alfadriver :

There may not be any catalyst related codes if the catalyst tests weren't running because of misfires or fuel trims out of whack.  There wouldn't even be any useful Mode 6 data because the last time the test would have run would have been a long time ago.

Not every manufacturer does, but some manufacturers do give you a list of monitors that won't run if a given code is set.

Sometimes it's even things that seem unrelated.  Many manufacturers (I know Ford is one of them) won't run misfire monitoring if the fuel level is below 10% or so.  They don't want to set an emissions failure because the fuel pump sucked air.  So.... what happens if you have a genuine misfire that it isn't looking for because you have a bad fuel sending unit that you don't care if the gas gauge isn't working?  Might set false fuel trim or catalyst codes. Or it might ignore those too.  But it's still damaging the converter.  And if it doesn't think the fuel level is between 15% and 85%, it won't run any evap tests either.

So you finally fix the bad sending unit or the wire that a rodent found tasty or whatever, six or eighteen months later, and suddenly you have a whole lot of new codes and you still can't pass emissions, because in the meantime the charcoal canister cracked or the fuel filler neck got porous or your oxygen sensors drifted mightily or the exhaust manifold bolts broke (but it's just an exhaust leak, who cares, it still runs fine...)

I see this ​​​​all the time.  The moral of the story is to fix E36 M3 when it breaks instead of ignoring the light because you don't need to worry about passing emissions for another two years.

(I have been told recently that when I opine, I opine hard.  Well, this is also why I feel a need to point out in every MIL inspection that some monitors may not have been running due to the present fault, and once that is fixed, other unseen problems may surface.  And some people see that as "you can't do your job you're supposed to find everything."  My crystal ball's in the crystal ball repair shop so I can't tell you that)

In reply to Pete. (l33t FS) :

So there would have been an ignored misfire code prior to the cam issue repair. Let alone, if there was enough misfire to "clog the cat", the car would have gone into a "limp home" prior to the original service. 
 

It seems to me that any reason that would have damaged the catalyst prior to the original repair, that should have been detected and flagged before the original service. 

In reply to alfadriver :

How do you detect it if the computer isn't even running the catalyst monitor?

Also, converter failure is interesting.  99 times out of 100 it flows perfectly fine but has lost efficiency.  200,000 miles of burning a quart of oil every 2000mi will do that.  But when they clog and pose a restriction, they oftentimes have sufficient efficiency in the part of the substrate that can flow that it will pass the catalyst monitors just fine.

One example in particular that sticks in my head was a Nissan NV2500 (the big huge van with a VQ40 six) that had a very clogged left side converter.  It was three years old and something like 40k miles, so it should have been under warranty.  Fuel trims were like +30 on the right and -30 on the left because the MAF reads all the air going into the engine but most of it was only going through the right bank.  We put a pressure gauge in place of the upstream O2 sensor and it would peg its 15psi stop just sitting there idling.  

The dealership refused to replace the converter under warranty because it was passing the catalyst monitors and pressure testing was not an approved method of testing a converter.

In reply to Pete. (l33t FS) :

If the misfire monitor is preventing the cat monitor, that would very much mean the engine is misfiring. So that code would have been ignored. But other than a dead misfire, the cat monitor would run. Either way, the shop had to ignore codes for previous damage to have been the root cause of the "clogged cat". 
 

As for your example, did the shop do the same test to determine it was a "clogged cat"?  
 

We are not being told if the car ran badly prior to the original repair. 

I agree, it would be nice to know the exact codes it had been setting, because I am curious about what the failure effects management is (thanks, Ford, for that wonderful terminology) as far as what it ignores when those specific codes are set.

It doesn't necessarily have to be misfiring to damage the converter.   Some Hyundai engines of the era had a lovely tendency to burn oil, which makes the rings stick, which makes them burn a ridiculous amount of oil.  There's a bulletin to basically perform an in cylinder engine soak to unstick the rings, and use 5W30 in the crankcase, and only replace the engine if that doesn't bring consumption to less than 1qt/1000mi.  But if the engine was ever burning a quart every 200 miles like they are wont to do, that will definitely hamper catalyst efficiency, even AFTER those things are addressed.  Maybe it isn't setting a code at 40k miles but the converters been hurt and its life has been shortened. 

I am also somewhat leery of anything a service advisor says as far as technical things go.  I have known enough advisors who called every refrigerant "Freon" that I take anything they say as merely a vector for finding out what the real issue is.   They may be saying "clogged cat" as shorthand for some other fault that has the same end result.

In reply to Pete. (l33t FS) :

A cat damaged with a lot of oil should trigger a cat efficiency code, or various O2 codes. 

In reply to Pete. (l33t FS) :

I had a S/A try to sell me a second tire because having a new tire and a worn tire of the same make and size would make my rear axle wear out.

Apparently "the gears won't be in mesh because the tires turn at different speeds"

I politely replied that is the purpose of a differential. 

In reply to ShawnG :

My most recent oil change, they asked me if I wanted a fuel and oil additive. I should have told him to use better oil if they are suggesting an additive.