Hey all,

Car: 99.0 a4 quattro 2.8L Base

So both of my cats have gone (very) bad over the past year. Extremely loud rattling and noticeable loss of power. I have been pondering whether to get a test pipe or a high flow cat and figured I'd ask you guys for opinions.

I'm reluctant to fit a HFC because I am also pulling codes P0441 and P0411 for the SAI system and EVAP control. From what I understand, the SAI helps blow extra o2 into the exhaust during cold starts to put less stress on the cats? If so, I don't want to install 2 new HFC's just to have them go bad from the failing SAI system down the road....

As far as the SAI sys is concerned, I've replaced all the hosing and confirmed the pump works. I am a bit lost as to where to continue diagnosing, I am just hoping it's not the combi valves...

If I were to install a test pipe, I've heard that it will run rich and continue to hurt fuel economy (currently avg. ~17mpg city...) however installing spacers in the downstream o2 sensors could help? Where would I find the right ones and how would they be installed, though?


Any opinions/thoughts would be much appreciated. Thanks!!

 

bump. :?

 

SAP airflow is read and reported by the secondary O2 sensors as they're the only sensors downstream of the cats. Your cats have definitely failed if they're rattling, and need to be replaced. I would replace the secondary O2s if you are positive the SAP system works, then clear the codes and see if they come back. If not, you're set and can put in cats. Test pipes may free a little power but if you have any emissions checks, you'll need spacers for the rear O2s or will need to code them out with a reflash of the computer.

 

Thanks for the reply! My state doesn't require emissions, so really I would be only be hesitant to just put test pipes in if it had any adverse effects on the engine. Would love to not drop the $$$ on new cats if at all possible.

 

You should get a turbo...That'll fix your problems

 

If only the 2.8 had a turbo kit......... heh

 

I'm tpying with a setup using several 1.8T parts. I have it drawn up and am collecting some pieces to possibly kick it up. More of a rainy day idea than anything but it seems pretty doable for an extra 40-50hp just to pep it up some.