i installed a full 2.5 borla exhaust system with 2.5 hi-flow cat and downpipe. After 4 days of the install, my check engine light went on. I thought it might have something to do with emissions.... So then the light went off and didnt think about it anymore. Then 2 days ago the damn thing came on again!!! There are no problems driving the car mechanically so im guessing the emissions sensor still?..... Any suggestions from you guys, and anyway to cancel it out so it stops turning on?

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Scan for codes. Could easily be an exhaust leak or the high flow cat might not be cleaning up the emissions enough. Did you install the gasket between the turbo and cat?

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2004 S4 6MT black *just bought
99.5 A4 1.8TQM red and 17" A6 4.2 wheels *sale pending
97 A4 1.8TQMS silver & lots of mods *totaled
96 A4 2.8M black *totaled

yah i installed all gaskets and the exhaust system is all welded together except downpipe and hiflow cat obviously. Checked for leaks after the install and everything was fine

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Yeah...thats the problem with high flow cats - they don't always satisfy emissions requirements. I would say, try using a spark plug non-fouler in the secondary (post-cat) o2 sensor. I used two for my testpipe, but one might do it for you.

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2004 S4 6MT black *just bought
99.5 A4 1.8TQM red and 17" A6 4.2 wheels *sale pending
97 A4 1.8TQMS silver & lots of mods *totaled
96 A4 2.8M black *totaled

what did you do with the sensor? If it wasnt pluged in-use wouldnt you have the same problem with the check engine light coming on?

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anyone else with this problem? I know a couple of you have the full borla exhaust from a while back...........................

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Sorry...the pic doesn't show the sensor. You just plug it in on the other side of the non-fouler. This is meant to take the sensor out of the main stream of exhaust flow, thus not picking up harmful measurements. You will also need to drill out the non-fouler a little bit for the sensor to fit.

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2004 S4 6MT black *just bought
99.5 A4 1.8TQM red and 17" A6 4.2 wheels *sale pending
97 A4 1.8TQMS silver & lots of mods *totaled
96 A4 2.8M black *totaled

streamline industries in salt lake they really need to get a website. but yea, theyhave these sensor spacers or somethin they put on mine and it hasnt turned back on since.

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2005 b6 a4
GIAC stage 1 chip
bilstien pss9 coilovers
evo ms intake
techtonic full exhaust with down pipe and race cat
stratmosphere diverter valve
forge silicon hose kit
brembo 332mm slotted 2 piece rotors with 4 piston calipers