Emmsions testing.. does synthetic oil read as HC?

[CrAlt]

I have a 1991 Dodge D150. I don't drive the truck much at all. Maybe once or twice a month for dump runs or to pull a trailer.

I have to have it smog tested to renew my reg. I failed on HC. I was allowed last time a reading of 200PPM on the HC. Now im only allowed 160 and the truck got 172.

It has 10w30 Supertech and burns a good amount of it. Its not visible under load but at light load or when it 1st starts it it very visible. They spin the truck on a dyno with no load on it and i think this is making it suck more oil.

Im guessing the smog machine is reading this oil as Hydorcarbons. Will it also read Full Synthetic as HC? I was thinking about changing to 20w50 Full Synthetic and maybe putting a 2nd cat in line behind the one thats in there.

The truck otherwise running as good as it can. Good ignition and clean air filter.

My NOX and CO are fine.

 

[HTSS_TR]

Did you have a good long drive on highway to bring the engine up to operating temperature ? I always had a 15-20 miles on the way to smog test station, when the engine is cold it run rich therefore a lot of unburnt gas go to tail pipe. HC is unburnt gas.

 

[NateDN10]

Partially burnt oil, synthetic or not, is a hydrocarbon. I'm not knowledgeable on emissions testing machines, but I'd assume that burning oil would contribute to the HC number.

 

[mechtech2]

Thicker oils burn less.
There will be a drag penalty, and a cold start penalty. In CA, the latter won't be too big a deal.
So thicker oil would go in the right direction.
I still don't know if you have a misfire here and there.
We are assuming it is only the oil burning in question.
Your 20 year old catalytic converter may be puked, as well.

Rich burning is a high CO reading, not HC. Misfires is HC, and maybe oil burning.

 

[The_Jeff]

fresh oil, day of smog, and HOT. You have a belt driven fan so just idling forever won't do it, you need to rocket up some hills. If you can swap in a hotter thermostat that would be very helpful. The oil will soak up HC for a little while. Thicker sounds good too.

 

[UNC017]

All oil is hydrocarbon, but I can't imagine that burning a little oil would actually raise the HC emissions level, since its so completely dominated by the HCs from *fuel*. Either your catcon wasn't fully warmed up for the test, or its not working quite right. As others have said a long hard highway run on the way to the emissions test is a good way to get much better HC numbers if you're borderline. Also trucks of that vintage are prone to have problems with the air injection system- make sure that its working so the catcon has enough O2 to work with to clean up the unburned HCs in the exhaust. Of course the other way trucks of that vintage can fail is an over-active air injection system that shows up as too much O2 in the exhaust.. ;-/

 

[2oldtommy]

As a rule, I always run a container of Techron Complete Fuel system Cleaner in the tank prior to testing. Cost, about $8.xx. This should do the job. FWIW--Oldtommy

 

[Steve S]

HC is a rich mixture /unburned gas. Reread 440 magnums post.

 

[brights_garage]

If this truck isn't driven often, how old is the fuel in the tank?

 

[2oldtommy]

As a rule, I always run a container of Techron Complete Fuel system Cleaner in the tank prior to testing. Cost, about $8.xx. This should do the job. FWIW--Oldtommy

 

[cchase]

If you are failing on HC and it is caused by oil, not fuel, you'd be able to see the smoke coming out the tailpipe.