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GS - 2nd Gen (1998-2005) Discussion about the second generation GS300, GS400 and GS430 (1998 - 2005)

P0446 code...

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Old Oct 11, 2012 | 12:21 PM
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You can block the exhaust from tailpipe and listen for hisses.


Originally Posted by sakataj
almost 150k....trust me no leaks up front, after installing new gaskets i used some exhaust silicon and wrapped it al the way around, havent checked after the cat as the O2 sensor wouldnt pick that up

i know how to smoke test a intake system.....how would you smoke test a exhuast system? maybe filling it with smoke from the tailpipe and pressurizing the tubing to see if its leaking?

the fouler would fix it either way, it pulls the O2 out of the "flow" so it wouldnt know the difference.
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Old Oct 11, 2012 | 03:21 PM
  #17  
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Originally Posted by sakataj
almost 150k....trust me no leaks up front, after installing new gaskets i used some exhaust silicon and wrapped it al the way around, havent checked after the cat as the O2 sensor wouldnt pick that up

i know how to smoke test a intake system.....how would you smoke test a exhuast system? maybe filling it with smoke from the tailpipe and pressurizing the tubing to see if its leaking?

the fouler would fix it either way, it pulls the O2 out of the "flow" so it wouldnt know the difference.
yes, smoke test from the rear. plug one pipe, smoke in the other.

when your car is testing catalyst efficiency, it intentionally changes from a lean to rich mixture and back again. this tests the oxygen holding capacity of the cats. the rear o2 sensors should have a delayed change after the mixture change whereas the fronts should change right away. if the rear 02's respond too similarly to the fronts or never really respond to the rich mixture, the ECM determines the catalyst is no longer efficient.

Exhaust leaks introduce oxygen into the exhaust system. even leaks up to 2 feet BEHIND the rear O2's can create false readings. it may be counter-intuitive, but it's true. Don't ask me exactly how the ECM does this, but this can cause a p0420 or p0430. if there is a p0606 code (says ECM malfunctions) also there, you really really need to check for exhaust leaks because the computer is seeing things that aren't possible and diagnosing itself as problematic

Originally Posted by cruisinvip
i get awful gas mileage with the po430, lack of power/response too
sounds like you have a definitely have a different issue. or 2 different issues. if you had a bad cat (unless it was clogged which is rare), there would be very little difference in driveability
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