OH man. I just calculated my mileage using this way: reset the odometer to zero @ fill up, fill tank to full and use Chevy's measurement of a full tank which according to my owners manual is 16.6 gallons. then drive till nearly empty and recheck odometer. 245 miles. That works out to 14.76 mpg. Ugghh
. That sucks. BTW, no CEL, new air, fuel filter. PCV was changed as well, oil change done recently plugs and wires are in good shape. Car hauls a** like you wouldn't belive, so I'm guessing the converter isn't plugged. Car was a NYPD /FDNY car all its life so was well taken care of. It's a 99 9c3 w/ 3.8 and recently rebuilt tranny (well actually a new GoodWrench tranny was put in by FDNY 3 months before selling). No slippage and I added an external cooler and the fluid is new. Tires are properly inflated and brakes are new and free wheeling, lol, thought about brake drag. Had it happen to me on a Nissan Z once. Any ideas? And also I have found my Loomie runs different on 87 vs 93 Sunoco, which I always put in. 93 it runs quicker, and idles smoother. And during this test I was extremely lightfooted on it using mixed highway and city 55, max.