Use biodiesel before emissions testing?

Every couple of years, Marylanders, at least those with cars registered in AA county, have to have their cars' emissions tested at one of the government facilities.

Would my TDI perform better (i.e. fewer toxic emissions) if I fill up with biodiesel beforehand?

Do they test NOx?

If so, bio will hurt you, unless you retard the timing beforehand.

If they only test opacity, go for it!

JamesBa said:

Every couple of years, Marylanders, at least those with cars registered in AA county, have to have their cars' emissions tested at one of the government facilities.

Would my TDI perform better (i.e. fewer toxic emissions) if I fill up with biodiesel beforehand?

Click to expand...

Most tests run on a diesel vehicle are for opacity, only. ie how bad does your car smoke.
Looking at the marylandmva website the test consists of an OBD examination only, if your car is >1995 vintage.

Montgomery County, and AFAIK, all of Maryland exempts diesels from Emissions test.

Even still... the test for 1996+ cars is an OBD2 Scan only. They check the "readyness" codes, and not just faults, so simply clearing codes won't make you pass.

I don't remember if my TDI has the same "Readyness" codes as my 96 gasser, so that might explain why Diesels are exempt, even though they are OBD compliant.