I've been chasing my tail trying to find the cause of the lower than expected/normal fuel economy in the wife's car. It's a 1995 Grand Am with the 3.1 V6, which was rebuilt recently (4k miles and some change) and the details of the build and back story can be viewed HERE. The only other thing not mentioned in that thread is that I replaced the fuel pump with a Delphi unit because the Carter replacement was making intermittent noises. The drop in fuel economy started before replacing the engine, but I chalked it up to old or bad sensors/high mileage and didn't investigate, knowing the engine would be replaced soon. Once the new engine was in place, the mileage never came up. She swears up and down her car used to average 27-30 mpg in combined driving (approx 80% hwy) and now it's getting 22-25. It's achieved 25 only a few times and 26 once. Otherwise it's 22-23mpg over the course of 4k plus miles in fairly consistent conditions. I've been waiting to purchase my latest toy (Snap On Solus Ultra) to go over the various values hoping to spot the darn gremlin... Now that I have it, I still can't find anything too out of the ordinary, but I do have a few questions... -Fuel trim. I'm not very familiar with the older systems. I know that it's based on a range of 0-256, with 128 being neutral. Going down the road, cruise on 55, fuel trim is around 125-130ish, so pretty normal? -LT trims - hovers in the high 1teens to low 120's, so around 117 to 123ish. Looks like the computer is trying to take some fuel out. - Trim Cell????? No clue.. Any input? -Throttle position is only around 12% cruising at 55mph, so it doesn't appear to be laboring. Other sensor values appear normal. Intake air and coolant temp are accurate within reason and the o2 sensor shows lots of activity. Switching to graph, it appears to have an even mix of rich and lean counts. My only other observation is that the exhaust does have a strong odor to it, but I don't know that it means too much because the car has no catalytic converter.