Originally posted by Theurig
Well my buddy, has a 1987 BMW which failed the extensive New Jersey emissions, before going through costly repairs, he put in this fuel system cleaner from Pepboys by the name : Guaranteed to Pass Inspection!! and sure enough he passed the second time round. I am not sure what it does to the system but he passed, His CO was down and were the Hydro Carbon readings.
These additives are a rip off. We took 20 cars that failed emissions by different degrees, slightly( .2 to .6 gpm) moderately ( .7 to 1 gpm) and a 'gross polluter' ( 1.2. to 3 gpm) added what is probably the same additive, retested them and the maximum improvement was only .2 gpm HC, .4 gpm CO- ( gpm=grams per mile of pollutant)
A well tuned vehicle of any make can have as much as 20% variation in emissions from test to test, when tested, the emissions levels are analyzed by the infrared and non-directional IR spectrometer at around 12000 readings per minute, from this data the sample mass or percent is calculated from a cummulative reading every 2 seconds, with a running average compared to a standard thatr may be a maximum cut point, a phase cut point based on distance traveled, or a statistical cut point based on emissions data from h8undreds of tests done on the same make ond model of vehicle.
The analyzer itself has a variation of 2.5 to 5%. depending on type. And in the case of refremista, if your shop had not calibrated his analyzer as per SOP's then it is hard to say how accurate his readings were.
The first thing to do as a fix is determine if the engine is in fuel control, if so and the HC CO reading s are still too high to pass but cannot be improved, then this might indicate a worn out catalytic converter. A good test is called an intrusive test where the O2 levels are sampled before and after the cat, if the are close, say 13.5 to 14 before and 15 of so after then the cat is not working, another way is to take CO2 readings at tailpipe without the O2 connected, if around 15% when tested in concentration or 100x more than HC if read in mass, then the cats OK.
adding ME(H2O) is not a fix, high CO indicates deviation from from stochiometeric fuel control thus a problem exists in emissions control components that may lead to drivability problems in the future.
Most of the fixes suggested here are a good place to begin with repairs that will enable your vehicle to pass the emissions test.