I have a 1999 Suburban 4 WD with the 5.7 Lt. gasoline engine. It needs a smog test. My scan tool showed a EGR malfunction. I removed the EGR and cleaned it and re-installed it. I cleared the trouble code and drove the vehicle for 30 miles with no trouble codes. When you clear the trouble codes on the vehicle computer this also causes several systems, such as the exhaust system and the fuel evaporative recovery system, to cycle through normal stop and start driving and engine warm-up cycles before the computer will allow them to reset and be tested by the smog machine. My problem is two of the systems will not reset. The Evap system resets after a little over a hundred miles of normal driving BUT the Cat/Exhaust and the Sec. Air will not reset after hundreds of miles of driving. I put over 750 miles on the vehicle the first time. I then disconnected the battery and reconnected and put another 300 miles on the vehicle with the same result. I tried this another time and have over 250 miles on the vehicle with the same result. I have talked to 2 dealership smog techs and they can offer no solution. A Service Manager, that I know, asked around and he told me that a tech told him that he had heard of this problem about 10 years ago and it was caused by a defective "fuel pressure" sensor on the gas tank. Is there such a sensor and can it be tested or re-placed? I would really appreciate any advice or help on this problem.
Chuck Davis