and HC is HC, really. whether it be from oil being combusted or gasoline. in fact, the HC in the oil comes from the gasoline by means of blow by.

i do see what he's saying though. it may be harder for the cat to extract the HC from burnt oil and break it down

i'm going through about 1.5 liters between oil changes.
For the oil light to come on, it would have to be down at least 2.5 or 3 liters.

Some of the 08-09 4 cyl Accords have been burning up oil to the point where the oil lights were coming on. We were to check the plugs for fouling. Some looked wet, black with deposits and some looked grayish with deposits. The fix for that was to replace pistons and rings. Its a very interesting job but glad i wont be doing any more of them. Very time consuming. I can't remember if those cars were even smoking when they came in. These cars were typically down a few liters or so.

As far as honda's are concerned, i never found an actual spec for what precat readings should be, but we have done testing on newer cars and found precat readings are typically around .5% CO and 50-60 hc at idle. Not enough to cause smoking. I can think of 2 reasons why it runs slightly rich. 1- they just run better slightly rich and 2- the converter needs a feed gas to "light off".
Come to think of it...the old early 80's carbs before converters were installed, when they were rebuilt or cleaned, i'd set to it 1-1.5% co after, even thogh the spec was to set to 1% or less, with no sign of smoking.

I don't think oil burning hc's are detected during aircare testing. Could be wrong tho. But i don't recall it showing up on our shop's exhaust sniffer.

good point, never really thought of that

it really depends on the condition of the oil that's being burned. a lot of times an oil burner will be the result of blowby. in which case the oil will usually be pretty rich with hc. one reason it's advised to give it afresh oil change just prior to testing

those precat readings are very nice. they don't seem rich at all really. actually typical of what you'd see from the tailpipe. very efficient!
personally when reading emissions though, i'd prefer to look at co2 and o2 before hc and co