The reason for not using most of these additives is due to the blend of gasoline ingredients combining with the bottle of what ever, and being poorly matched....very much like oil additives. Additives will/can upset the combustion and produce affects on the readings for emissions tests.
There is one product that guarantees a lower tail pipe reading............
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http://www.rxp.com/Auto-Ad.htm
I have not used it but some here might have.
Older vehicles will not pass due to crank case blow by or the CHECK ENGINE lite is on.
Vehicles that typically get low miles per gallon are hard to get a pass.
There is a new test that does not use tail pipe gases being studied.
They claim t/p tests don't tell the whole story of how efficient an engine is.
http://blogs.rockymountainnews.com/denver/rockytalklive/archives/2006/05/no_more_tailpipe_testing.html
This is another reason E85 fuel is being pushed .
http://www.ucsusa.org/clean_vehicles/vehicles_health/the-plain-english-guide-to-tailpipe-standards.html
( See my other thread..
http://www.peachparts.com/shopforum/showthread.php?t=161092 )
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