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Aftermarket converter...tricking the ECM for emissions.


Top_Notch
04-22-2013, 08:46 AM
Just thought I'd share as I read this trick on another board and it's worked for me. I can do a better write up with pictures if anyone wants.

I own a 2002 Monte with the 3.8 NA. At about 90,000 miles the cat broke up and caused drivability issues. I had the cat replaced by my local mechanic and subsequently learned that there was an extended warranty since this was a known problem for many of these cars. (GM refunded me the money for the aftermaket cat)

Problem was that after a year I have a CEL related to the Cat. Turns out the replacement cat is less restrictive than the Generals brand. You may know already, but on the years where the ECU doesn't change fuel trims based on the rear o2 readings, it's possible to keep the aftermarket cat by tricking the ECU. Basically, you take a spark plug fouler to get the rear 02 sensor away from the exhaust stream. I've seen a lot of tutorials online showing they double up the spark plug foulers, but with the u-bend exhaust, I wasn't sure there was enough room beneath the floorboard and the 02 sensor.

So I took one Dorman Spark plug fouler (Part 42009) and drilled out the bottom with a 5/8 drill to fit the sensor. Then just replace the sensor. So far it's working great and I just checked after I cleared the codes and all the diagnostic tests were run and I am now emissions compliant. Great trick and cost all of $5. (I had to reset twice because I got an EVAP code so I reset the codes once again and cranked down my gas cap and now all is good)

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