Question about 1999 GMC Yukon
The previous owner had removed the catalytic convertor system and installed a straight through exhaust system with "cherry Bombs" on it. I did not think this was a problem (other than noise) until I checked the codes and kept finding an O2 sensor problem on a brand new sensor. The straight exhaust was allowing the exhaust gas to flow by so quickly the O2 sensors heating element could not heat properly and maintain the temp so the motor would richen the mixture, flooding the plugs. You shut down the PCM for a few minutes and restart with a fresh set of paramaters again until the O2 sensors were called for. I installed a piece of 1.25" pipe by 12" long between the pre and post catayltic sensors to simulate the flow impedance of a convertor, reset the codes and the truck runs great. The backpressure allows the sensors to attain proper temp and stay there so the PCM can regulate the mixture as needed. I am currently waiting for the new converotors and stock muffler/pipe system to come in to my auto parts supplier so I can bring the unit back to design standards. I thought there were no new codes, but I was wrong. I did not wait long enough for the codes to go from "pending" to "set" position. I also found my scanner does not reveal "pending" codes. Time for a new(better) scanner.
Posted on Jul 18, 2008
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