Three GM city buses have been equipped with the GM Truck and Coach Environmental Improvement Proposal retrofit kit and operated approximately 25,000 miles. Noise tests were made before and after kit installation. With regard to odor, smoke, and other tailpipe emissions, the Low Sac Needle injectors were found to give consistently and substantially lower smoke, odor, HC, CO and oxygenates during this initial 25,000-mile-test period. The catalytic muffler, one item included in the EIP kit, was found to be largely ineffective in reducing emissions. The vertical stack has the effect of making odor and noise less noticeable to the man-in-the street, but may make smoke more visible. These findings are in agreement with component studies conducted during the past 2 years with the catalytic muffler and improved injectors.