He has a 2006 Trail Blazer SS. Since with the emission test here they just hook his truck to a OBDII plug, if the car does not throw any codes, how would the machine know the emissions are bad?

He has a friend who is tuner and belongs to the local SS club. Several of them have high flow cats and said there is no issue. What you said about a tunes engine makes sense though. No way my car would pass. Two more years and I do not have to worry about it any more. She will be a 25 yr old classic and I am exempt.

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2014 C250 21,XXX my new DD ** 2013 GLK 350 18,000 Wife's new DD**

- With out god, life is everything.
- God is an ever receding pocket of scientific ignorance that's getting smaller and smaller as time moves on..." Neil DeGrasse Tyson
- You can pray for me, I'll think for you.
- When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours.

here in phx if you are 96 and newer obd2 they do not smog your vehicle. they hook it up to the computer, look to see if the check engine light has been on and if all clear you pass.

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All OBDII cars (1997 to present) have 2 O2 sensors - one upstream of the Cat conv. and one downstream. The ECU periodically checks the two readings to be sure that the cat is actually 'cleaning' the exhaust going through it. If you just delete the cat on an OBDII car (with a stock ECU...) then it'll throw a cade saying "Catalytic converter isnt working properly" - this would be a code that, if discovered, would cause you to fail most emissions checks.

And then about the tailpipe sniffs- ask the diesel guys how sleazy those are - when I had my OM617.951 and Ohio was sniffing it for Opacity - the limit was 20%, and my 'burned 1qt oil per 3k' read out at 3% - I could have been making clouds of black smoke and probably passed the emissions sniff. While gas cars have different tests (CO content, NOx's...etc..) they actual limits might not be very restrictive - this would cause some old/out of tune cars to pass a tailpipe sniff with flying colors. I must assume that the limits for tail-pip sniff failures are different from state to state.
I've heard of places/businesses that will re-flash an ECU to 'forget to check' the cat's, but I'm very sure that such a thing would be 'for off road use only'. I know that no one here would every illegally modify their engine's emissions controls.

=)

bottom line - you need to see how your state does emissions checks (Ohio used to to do both- OBD check AND tailpipe sniff) and plan accordingly. If the car being tested is 1996 or older, there is no way the state can check it's OBD computer for codes so its a sniff or nothing.

-John

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several people on here have posted the way around the 02 sensors. it is possible to pass the emissions test without cats.

__________________
have no worries.....President Obama swears "If you like your gun, you can keep it